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Journal of Chromatography A
Journal Prestige (SJR): 1.378
Citation Impact (citeScore): 4
Number of Followers: 128  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0021-9673
Published by Elsevier Homepage  [3161 journals]
  • Qualitative analysis of dental material ingredients, composite resins and
           sealants using liquid chromatography coupled to quadrupole time of flight
           mass spectrometry
    • Abstract: Publication date: Available online 21 September 2018Source: Journal of Chromatography AAuthor(s): Philippe Vervliet, Siemon de Nys, Imke Boonen, Radu Corneliu Duca, Marc Elskens, Kirsten L. van Landuyt, Adrian CovaciAbstractSince 2011, the World Health Organization has encouraged a global phase-down of the use of dental amalgam and actively supported the use of alternative, resin-based dental materials. The resins consist of (meth)acrylate monomers derived from Bisphenol A (BPA), such as Bisphenol A glycidyl methacrylate (BisGMA) and Bisphenol A ethoxylate methacrylate (BisEMA) or triethylene glycol dimethacrylate (TEGDMA) and urethane dimethacrylate (UDMA) which lack the BPA backbone. Besides monomers, other compounds such as photoinitiators and stabilizing agents can be present in the dental resin matrices. The current study consists in the development of an analytical method for the separation and identification of dental material components using LC-QTOF-MS. The developed method was applied on several dental material ingredients, unpolymerized composite resins, and a common dental sealant. The acquired high resolution accurate-mass data was analyzed using suspect screening with an in-house developed library. Next to the main components, various isomers and impurities related to the production of the main component have been detected and identified in the dental material ingredients. In total, 39 chemicals have been identified in the analyzed dental materials. On average 15 chemicals have been identified. Major components, such as BisEMA, BisGMA and TEGDMA were identified although they were not always stated in the material safety data sheets. Minor components included photoinitiators, such as ethyl 4-dimethyl aminobenzoate (EDMAB) and (meth)acrylates impurities originating from production of main ingredients.
       
  • The synthesis of Zr-metal-organic framework functionalized magnetic
           graphene nanocomposites as an adsorbent for fast determination of
           multi-pesticide residues in tobacco samples
    • Abstract: Publication date: Available online 21 September 2018Source: Journal of Chromatography AAuthor(s): Rongrong Jin, Fenqi Ji, Huaqing Lin, Chen Luo, Yaoming Hu, Chunhui Deng, Xiujun Cao, Chunfu Tong, Guoxin SongAbstractIn this paper, a simple and reliable method has been established to determine the residues of nine pesticides in tobacco by using GC-MS coupled with magnetic solid phase extraction. A novel magnetic Zr-MOF nanocomposite based on graphene was synthesized, and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy and N2 adsorption-desorption measurements. The prepared material has the advantage of large surface area (178 m2/g), good magnetic response and high thermal stability, which is shown to be suited for the fast enrichment of multi-pesticides in tobacco matrix. The extraction conditions including amount of adsorbent, adsorption time, eluting solvent as well as desorption time were investigated. The whole process of pretreatment is accomplished within 10 min. This method shows low limit of detection, wide linear range and good reproducibility (relative standard deviations
       
  • Analysis of degradation products of nerve agents via
           post-pentafluorobenzylation liquid chromatography-tandem mass spectrometry
           
    • Abstract: Publication date: Available online 21 September 2018Source: Journal of Chromatography AAuthor(s): Mai Otsuka, Koichiro Tsuge, Yasuo Seto, Hajime Miyaguchi, Masanobu UchiyamaAbstractIn the work reported here, a screening procedure was developed for the detection and identification of RMPAs (nerve agent degradation products) after pentafluorobenzylation using liquid chromatography-tandem mass spectrometry (LC-MS/MS). With this method, all RMPAs, including highly hydrophilic types such as methylphosphonic acid (MPA) and ethyl methylphosphonic acid (EMPA), were sufficiently retained in commonly used reversed-phase columns (retention times: 15.7 and 11.0 min.), and the presence of RMPAs was determined more efficiently than with the conventional direct LC-MS/MS method. The detection limits of RMPAs using this approach (< 33 ng) were mostly superior to those observed with direct LC-MS/MS (
       
  • Phosphorous-enriched knitting aryl network polymer for the rapid and
           effective adsorption of aromatic compounds
    • Abstract: Publication date: Available online 19 September 2018Source: Journal of Chromatography AAuthor(s): Qianqian Wang, Lihong Zhang, Lin Hao, Chun Wang, Qiuhua Wu, Zhi WangABSTRACTA phosphorous-enriched knitting aryl network polymer (named as Ph-PPh3-KAP) was fabricated by one-step crosslinking between triphenylphosphine and benzene, with formaldehyde dimethyl acetal as an external crosslinker. The Ph-PPh3-KAP had a large surface area and good physicochemical stability. Its adsorption performance for aromatic organic compounds was evaluated by using some dyes and benzene ring-containing compounds as the model adsorbates. The results exhibited that it had a rapid and effective adsorption for the aromatic organic compounds due to the hydrogen bonding and polar interactions of the Ph-PPh3-KAP with the target compounds. Then, the Ph-PPh3-KAP was explored as the adsorbent for the solid phase extraction of some phenylurea pesticides from lake water, tomato and cucumber samples prior to HPLC analysis. Under optimal conditions, the linear responses of the phenylurea pesticides were 0.1-100 ng mL-1 for lake water and 0.5-100 ng g-1 for cucumber and tomato samples. The limits of detection for the analytes at S/N = 3 were 0.01-0.02 ng mL-1 for lake water and 0.03-0.05 ng g-1 for cucumber and tomato samples. The recoveries were in the range from 80.8% to 118%. The Ph-PPh3-KAP exhibited a great application potential for extraction of aromatic compounds.
       
  • Endotoxin reduction in protein solutions using octyl
           β-D-1-thioglucopyranoside wash on chromatography media
    • Abstract: Publication date: Available online 18 September 2018Source: Journal of Chromatography AAuthor(s): Dhanesh Gadre, Marcia Carlson, Ashley Mullan, Ivy Kabundi, Nichole Pedowitz, Sadiye Amcaoglu Rieder, Natalie White, Kathy Yu, Ellen O’ConnorAbstractEndotoxins are complex molecules and one of the most challenging impurities requiring separation in biopharmaceutical protein purification processes. Usually these contaminants are cleared during the downstream process, but if endotoxin interacts with the target protein it becomes difficult to remove. In the present study we identified a detergent, octyl-β-D-1-thioglucopyranoside (OTG), that disrupted endotoxin-protein interactions. The integration of this detergent into washes on several chromatography media was demonstrated to provide a separation tool for decreasing endotoxin from target proteins. This study also examined the mechanism of OTG endotoxin-protein disruption through phase modification incubation and chromatographic studies. The non-ionic OTG wash was shown to break both hydrophobic and electrostatic interactions between the endotoxin and protein. This mechanism contrasts with the breaking of hydrophobic interactions by washing with known endotoxin decreasing Triton X-100 detergent. The difference in mechanisms likely results in the ability of OTG to decrease endotoxin to levels less than those resulting from a detergent wash such as Triton X-100. Finally, we show the impact of the OTG endotoxin removal tool on the biopharmaceutical industry. While maintaining monomer purity and activity levels, endotoxin removal from a fusion protein allowed for decreased background levels in a T cell functional assay. The lowered baseline of T cell responses allowed for more effective detection of molecular interaction with the cells. The detergent wash can be used to both decrease the overall level of endotoxin in a purified protein solution and to enable more effective screening of lead candidate molecules.
       
  • A fully automated approach for the analysis of 37 psychoactive substances
           in raw wastewater based on on-line solid phase extraction-liquid
           chromatography-tandem mass spectrometry
    • Abstract: Publication date: Available online 18 September 2018Source: Journal of Chromatography AAuthor(s): Ester López-García, Nicola Mastroianni, Cristina Postigo, Damià Barceló, Miren López de AldaABSTRACTThis work presents a multi-residue method for the simultaneous determination of 37 legal and illicit psychoactive substances in wastewater, including the most common illicit drugs (cocaine-related compounds, amphetamine type stimulants, hallucinogens, opiates/opioids, and cannabinoids), new psychoactive substances (two synthetic cathinones, the synthetic opioid AH-7921 and the arylcyclohexylamine methoxetamine), and legal but controlled psychoactive substances (stimulants, benzodiazepines, antidepressants, sedatives, antipsychotics and hypnotics). To this end a fully automated analytical approach based on solid phase extraction coupled in series to liquid chromatography tandem mass spectrometry detection (on-line SPE-LC-MS/MS) was used. The methodology developed was validated in terms of linearity, recovery, repeatability, and sensitivity in wastewater. Method linearity was between 0.1 ng/L (or the analyte limit of quantification if higher) and 2000 ng/L (10250 ng/L in the case of caffeine). Absolute recoveries were variable (between 5% and 132%), depending on the analyte. However, the use of isotopically labeled compounds corrected for analyte losses during the extraction process and matrix effects (relative recoveries within the range of 80-120%). Repeatability of the method was satisfactory for all analytes, with RSD values lower than 13% for most compounds. Limits of detection and quantification in wastewater were below 7 and 23 ng/L, respectively, for all analytes except lormetazepam (10 and 32 ng/L), caffeine (13 and 44 ng/L), and the cannabinoids 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (18 and 61 ng/L) and 11-hydroxy-Δ9-tetrahydrocannabinol (69 and 228 ng/L). The method was applied to the analysis of wastewater samples collected daily in Barcelona for one week. Twenty-five of the 37 analytes were detected in the samples analyzed. Average concentrations ranged from 7 ng/L in the case of zolpidem to 54 µg/L in the case of caffeine.
       
  • Development of a folic acid molecularly imprinted polymer and its
           evaluation as a sorbent for dispersive solid-phase extraction by liquid
           chromatography coupled to mass spectrometry
    • Abstract: Publication date: Available online 18 September 2018Source: Journal of Chromatography AAuthor(s): Peter Panjan, Romina P. Monasterio, Alegría Carrasco-Pancorbo, Alberto Fernandez-Gutierrez, Adama M. Sesay, Jorge F. Fernandez-SanchezAbstractThis work shows the development of a molecularly imprinted polymer to determine folic acid (FA) in food extracts by using dispersive solid-phase extraction and liquid chromatography coupled to mass spectrometry (LC-MS). Herewith, combinations of monomers (methacrylic acid (MAA), 4-vinylpyridine (4VPy) and vinylbenzyl trimethylammonium chloride (VBTMAC)) and crosslinkers (ethylene glycol dimethacrylate (EGDMA) and divinyl benzene (DVB)) were tested in appropriate solvents. Isotherm tests revealed that the MIP with the highest affinity was obtained by combining VBTMAC and EGDMA. Having checked the appropriate template-monomer-crosslinker ratio, the FA MIP was analyzed for its kinetic and equilibrium binding properties, proving very high affinity (more than 2.5 mmol g-1) and MIP/NIP ratio (up to 37). The FA MIP was used to selectively isolate the compound of interest from lettuce and cookies matrices using a dispersive solid-phase extraction protocol (which exhibited appropriate recovery and repeatability, ≥ 79.50% and ≤ 13.41 (%RSD in terms of area values), respectively, as well as absence of matrix effect); the resulting extracts were analyzed by a rapid and reliable LC-MS method.
       
  • Investigation of steric transition with field programming in frit inlet
           asymmetrical flow field-flow fractionation
    • Abstract: Publication date: Available online 18 September 2018Source: Journal of Chromatography AAuthor(s): Young Beom Kim, Joon Seon Yang, Myeong Hee MoonAbstractSteric transition in flow field-flow fractionation (FlFFF) was investigated under field programming by varying the channel thickness of a frit inlet asymmetrical FlFFF (FI-AF4). Steric transition is a typical inversion in sample elution mode from the increasing order of diameter (normal mode) to the opposite order (steric mode). Owing to the co-elution of two different-sized particles in the steric transition region where particles elute by the combination of the two elution modes, a loss of information in determining the accurate size of sample components in field-flow fractionation occurs. In this study, the effect of field programming on the steric transition in FI-AF4 was examined with the increase in channel thickness in order to increase the diffusional contribution of particle retention with the simultaneous reduction of steric contribution. This study demonstrated that the steric inversion diameter can be increased to> 1 μm by programming the crossflow rate and by increasing the channel thickness to 350 and 490 μm. The present study also investigated the effects of outflow rate and initial field strength on the particle separation in field-programmed FI-AF4.
       
  • Influence of Charged Aerosol Detector instrument settings on the
           ultra-high-performance liquid chromatography analysis of fatty acids in
           polysorbate 80
    • Abstract: Publication date: Available online 18 September 2018Source: Journal of Chromatography AAuthor(s): Klaus Schilling, Ruben Pawellek, Katherine Lovejoy, Tibor Muellner, Ulrike HolzgrabeAbstractThe analysis of polysorbate 80 is a challenge because all components lack a chromophore. Here, an ultra-high-performance liquid chromatography system equipped with a charged aerosol detector (UHPLC-CAD) was used to study the effect of systematic variation of the CAD settings, namely evaporation temperature, filter constant and power function value (PFV), on the detector response of fatty acid standards and manufacturing batches of polysorbate. Evaporation temperature and filter constant strongly affect the detection limits described by signal-to-noise (S/N) ratios. Although evaporation temperature can be increased to improve signal to noise ratios, analyte volatility at higher temperatures is an important limiting factor. The PFV was found to be a strong tool for optimizing response linearity, but the optimal PFV differed depending on analyte volatility. Because PFV optimization required some additional measurement time and because double-logarithmic transformation at the default PFV of 1.0 yielded satisfying universal results with less measurement time over a range of two orders of magnitude for every homologue fatty acid from C14 to C18, use of the log-log transformation is the favored linearization strategy. Possible optimization procedures for semi volatile substances are presented. Overall, this new UHPLC method method offers improved detection limits, as well as time savings of over 75% and eluent savings of more than 40% compared to the previously published HPLC-CAD method for polysorbate analysis.
       
  • Magnesium-aluminum-layered double hydroxide-graphene oxide composite
           mixed-matrix membrane for the thin-film microextraction of diclofenac in
           biological fluids
    • Abstract: Publication date: Available online 17 September 2018Source: Journal of Chromatography AAuthor(s): Milad Ghani, Sayed Mehdi Ghoreishi, Mostafa AzamatiAbstractHerein, the applicability of Mg-Al-layered double hydroxide-graphene oxide (LDH/GO) mixed-matrix membrane (MMM) for microextraction purposes is reported for the first time. The LDH/GO MMM was used as sorbent for the thin film microextraction (TFME) of diclofenac in human body fluids. The prepared LDH/GO composite has been incorporated into a mechanically stable polyvinylidene difluoride (PVDF) membrane. The contribution of GO in LDH/GO composites significantly improved the extraction efficiency of the TFME sorbent. After elution with methanol, diclofenac was quantified by high performance liquid chromatography-ultraviolet detection (HPLC-UV). A Plackett–Burman design was used for screening the experimental factors of interest and specify the significant variables affecting the extraction efficiency. The effective factors were optimized using Box-Behnken design (BBD). Under the optimum conditions, limits of detection (LODs) were 0.14, 0.23 and 0.57 µg L-1 in water, urine and plasma samples, respectively. Limits of quantification (LOQs) were 0.46, 0.76 and 1.8 µg L-1 in water, urine and plasma samples, respectively. Relative standard deviations (RSDs) at a spiked concentration of 10 µg L-1 were 6.7, 6.9 and 7.1 % (as intra-day RSD) in water, urine and plasma samples, respectively. The linear dynamic ranges (LDRs) were in the range of 0.5-200 µg L-1. The applicability of the method was investigated by the extraction and determination of diclofenac in different biological fluids including urine and plasma samples.
       
  • Optimization of production rate, productivity, and product concentration
           for a simulated moving bed process aimed at fucose separation using
           standing-wave-design and genetic algorithm
    • Abstract: Publication date: Available online 17 September 2018Source: Journal of Chromatography AAuthor(s): Sungyong MunAbstractThe effectiveness of a simulated moving bed (SMB) technology in the continuous separation of fucose from a multi-component monosugar mixture, which stemmed from defatted microalgae, has recently been identified. To guarantee high economical efficiency of such fucose-production method, the comprehensive optimization of the relevant fucose-separation SMB process needs to be accomplished such that its production rate (Prate) and/or productivity (Prod) can be maximized while meeting the requirements on fucose product concentration (Cprod,F) and pressure drop (ΔPSMB). To resolve this issue, the SMB optimization program based on standing-wave-design method and genetic algorithm was prepared and then applied to the fucose-separation SMB optimization. It was found that the Prate, under a given particle size, could reach its maximum when the column length was selected to create a balance between the effects of the two limiting factors related to Cprod,F and ΔPSMB. It was also found that the Prate was governed by fucose yield, if the SMB would be in need of a relatively high Cprod,F; otherwise, the Prate was governed by feed flow rate. If the particle size of the SMB adsorbent was fixed at one of the commercially available ones, the SMB conditions leading to the highest Prate and the highest Prod coincided with each other. By contrast, if the particle size was included as one of optimization variables, the Prate and Prod represented a trade-off relationship. Finally, it was confirmed from the simultaneous optimization for Prate and Prod that the increase of particle size improved Prate at the cost of Prod, thereby causing the maximum Prod to be always attained at a smaller particle size than the maximum Prate regardless of the target Cprod,F level.
       
  • Interfacing nanoliter liquid chromatography and inductively coupled plasma
           mass spectrometry with an in-column high-pressure nebulizer for mercury
           speciation
    • Abstract: Publication date: Available online 17 September 2018Source: Journal of Chromatography AAuthor(s): Heyong Cheng, Wenwen Zhang, Yuanchao Wang, Jinhua LiuAbstractMetal speciation analysis of microsamples in the clinical, biological and forensic fields is important for elucidating the metals’ toxicity, mobility and metabolic behaviors of metals. Such analysis may be achieved by nanoliter high-performance liquid chromatography (nanoHPLC) hyphenated with inductively coupled plasma mass spectrometry (ICP-MS). In this work, an in-column high-pressure nebulizer (ICHPN) was developed to enhance the sensitivity and the separation efficiency of the sheathless nanoHPLC-ICP-MS coupling. The ICHPN consists of two concentric fused-silica capillaries with tapered tips connected via a PEEK tee, where C18 silica particles with a size of 5 µm were packed in the tapered inner capillary based on the keystone effect. Combining a heated single pass spray chamber with a makeup gas, the ICHPN was capable of independently optimizing the nebulization efficiency and the transport efficiency. The ICHPN offered high sensitivities, low detection limits and good precision at nanoflow rates. Compared with commercial nebulizers, the ICHPN fabrication was simple, rapid, reproducible and inexpensive. By implementing the ICHPN, we achieved rapid separation of four mercury species, i.e., Hg2+ and methyl-, ethyl- and phenylmercuric chloride, within 8.0 min with good resolution (2.0-13.9). Detection limits of 0.044-0.13 μg L-1 were obtained with precisions of peak heights and areas ranging from 1.5-3.5% for a 50 μg L-1 standard solution. Good agreement between the determined and certified values of mercury species in a certified reference material of caprine blood (SRM 955c) together with good recoveries (93-101%) validated the accuracy of the method.
       
  • Determination of perfluorinated compounds, bisphenol A, anionic
           surfactants and personal care products in digested sludge, compost and
           soil by liquid-chromatography-tandem mass spectrometry
    • Abstract: Publication date: Available online 17 September 2018Source: Journal of Chromatography AAuthor(s): Concepción Abril, Juan Luis Santos, José Luis Malvar, Julia Martín, Irene Aparicio, Esteban AlonsoAbstractA method for the determination of 23 emerging concern pollutants in digested sludge, compost and soil has been developed. Target pollutants include six perfluorinated compounds (5 perfluorocarboxylic acids and perfluorooctanesulfonic acid), the plasticizer bisphenol A, four anionic surfactants (sodium alkylsulfates), four preservatives (parabens), two antimicrobial agents (triclosan and triclocarban) and six UV-filters (benzophenones). Sample treatment was based on ultrasound-assisted extraction with 3 mL of methanol:acetic acid (95:5, v/v) and clean-up by dispersive solid-phase extraction (d-SPE) with C18. Analytical determination was carried out by liquid chromatography-tandem mass spectrometry. Extraction solvent, sonication time, number of extraction cycles and type and amount of d-SPE sorbent were optimized. Due to the physical-chemical properties of target compounds, and the high number of sample treatment variables involved, a Box-Behnken design was applied to method optimization. The method was validated by means of spiked samples. Method detection limits were in the range from 0.01 to 6.2 ng g-1 dry matter. Accuracy and precision were evaluated at three spike levels in each type of sample matrix. Accuracy, expressed as relative recovery, was in the range from 70% to 120% for most of the compounds and spike levels. Precision, expressed as relative standard deviation, was equal or below 21%. To the best of our knowledge, the proposed method constitute the first analytical method for multiclass determination of emerging pollutants in digested sludge, compost and soils.
       
  • Analysis of calystegines in tomato-based products by liquid
           chromatography-Orbitrap mass spectrometry
    • Abstract: Publication date: Available online 17 September 2018Source: Journal of Chromatography AAuthor(s): Ana Romera-Torres, Roberto Romero-González, José Luis Martínez Vidal, Antonia Garrido FrenichAbstractTaking into account the high consumption of tomato and tomato-based products, a study of the occurrence of 7 nortropane alkaloids (calystegines A3, A5, B1, B2, B3, B4 and C1) in this type of matrix has been performed. For that purpose, a simple and fast solid-liquid extraction with methanol/water (50/50, v/v) has been developed, and then liquid chromatography, using an HILIC-A as stationary phase, coupled to high resolution mass spectrometry (LC-HRMS-Orbitrap) has been used for their determination. The developed method was validated and recoveries ranged from 96 to 121 %, and relative standard deviations lower than or equal to 16 % were obtained. Limits of quantification (LOQ) were established at 0.1 (B4), 0.25 (B3) and 0.5 (A3, A5, B1, B2 and C1) mg/kg. Twelve different samples were analyzed, comprising 4 crushed tomatoes, 4 fried tomatoes and 4 jam tomatoes. Calystegines A3 and B2 were identified in all the analyzed samples, while calystegine B3 was determined in all the fried tomatoes as well as in two crushed tomatoes and one jam tomato at concentrations ranging from 0.4 mg/kg (calystegine B2) to 19.0 mg/kg (calystegine A3). Although calystegine A5 was also detected in all the samples, only 3 of them gave concentrations higher than LOQ. Additionally, calystegine B1 was found in one jam tomato at 1.9 mg/kg.
       
  • Direct analysis of chiral active pharmaceutical ingredients and their
           counterions by ultra high performance liquid chromatography with
           macrocyclic glycopeptide-based chiral stationary phases
    • Abstract: Publication date: Available online 17 September 2018Source: Journal of Chromatography AAuthor(s): Omar H. Ismail, Michela Antonelli, Alessia Ciogli, Michela De Martino, Martina Catani, Claudio Villani, Alberto Cavazzini, Michael Ye, David S. Bell, Francesco GasparriniAbstractIn this work the simultaneous separation of chiral active pharmaceutical ingredients (API) in salt form from their counterions has been performed by using different high-efficiency macrocyclic glycopeptide-based chiral stationary phases (CSPs). Not only a new zwitterionic vancomycin-based CSP has been prepared (similarly to what was done for teicoplanin) but macrocyclic selectors have also been bonded to sub-2 µm fully porous silica particles through traditional ureidic linkage to obtain versions of CSPs suitable for ultra-high performance applications. The direct separation of chiral APIs and counterions is particularly attracting since it simplifies the workflow traditionally used with reduction of analysis time and costs. The wide selection of macrocyclic antibiotics CSPs now available has allowed to manage different cases that can happen in the simultaneous separation of APIs and their counterions (either cations or anions). Indeed, while inorganic cations are retained on traditional vancomycin- and teicoplanin-based CSPs, inorganic anions are almost unretained (due to Donnan’s effect). On the other hand, cations and anions can be both retained on the zwitterionic versions of these CSPs. Afterwards, zwitterionic CSPs allowed the separation of other compounds including N-derivative amino-acids, profens, polyols, sugar anomers, oligosaccharides and inorganic anions/cations opening new perspectives in the use of this family of CSPs.
       
  • Spectral Skewing in Gas Chromatography-Mass Spectrometry: Misconceptions
           and Realities
    • Abstract: Publication date: Available online 17 September 2018Source: Journal of Chromatography AAuthor(s): Andrey SamokhinAbstractIn the field of gas chromatography-mass spectrometry, linear quadrupole instruments remain the most popular. Quadrupole mass spectrometers are scanning instruments. It means that ions with different m/z values pass through the quadrupole sequentially. When analyte concentration changes during scan period, recorded mass spectrum is distorted. This phenomenon is called spectral skewing. There are two misconceptions associated with the spectral skewing: (1) the spectral skewing can affect the results of library search; (2) bilinear chemometric methods are often applied to skewed (distorted) GC/MS data to perform automatic data processing. We attempt to clarify these misconceptions. We can conclude that even strong distortion of mass spectrum (caused by the spectral skewing) practically does not change efficiency of automatic search against mass spectral database. On the other hand, even minor distortion of data (caused by the spectral skewing) can significantly distort results of automatic data processing (especially in the case of minor components). Interactive Excel files (presented in supplementary material) illustrate our findings.
       
  • A efficient method to identify cardioprotective components of Astragali
           Radix using a combination of molecularly imprinted polymers-based knockout
           extract and activity evaluation
    • Abstract: Publication date: Available online 17 September 2018Source: Journal of Chromatography AAuthor(s): Jing Xie, Jing Xiong, Li-Sheng Ding, Li Chen, Hua Zhou, Liang Liu, Zhi-Feng Zhang, Xue-Mei Hu, Pei Luo, Lin-Sen QingAbstractAlthough herb medicines have become the major source for new drug discovery, many of them are largely under-explored due to the purity-activity relationship. Efficient identification of bioactive compounds in conventional stepwise separation and isolation has not yet been elucidated. Therefore, we proposed a new separation strategy for holism understanding of herb pharmacology using molecularly imprinted polymers (MIPs). Astragali Radix (AR), important in traditional Chinese medicine, was chosen in this study for multicomponent knockout followed by bioactivity evaluation. We prepared calycosin molecularly imprinted polymers (calycosin-MIPs) which could selectively recognize flavonoid aglycons in AR. The molecular selectivity of calycosin-MIPs as a critical parameter was evaluated using the template and other high content compounds in AR. Based on it, using the calycosin-MIPs material via solid-phase extraction procedures was applied for the knockout of flavonoid aglycons in AR. Finally, hypoxia/reoxygenation model in H9c2 cells used to evaluate the activity of the AR extract before and after the knockout. The results showed that calycosin-MIPs as recognition materials for flavonoid aglycons in AR are applied in one-step separation with high selectivity and tunability. The subextract in the absence of flavonoid aglycons has been demonstrated to clarify the cardio-protective components of AR. In conclusion, this proof-of-principle study is the first one showing that molecular imprinting technology coupled with a bioassay can be used to explore the bioactive variability from the perspective of multicomponent separation of herbal medicine.
       
  • Zr-based metal-organic framework-modified cotton for solid phase
           micro-extraction of non-steroidal anti-inflammatory drugs
    • Abstract: Publication date: Available online 17 September 2018Source: Journal of Chromatography AAuthor(s): Wenqing Li, Rong Wang, Zilin ChenAbstractA novel metal-organic framework UiO-66-modified cotton was prepared and applied to solid phase microextraction of non-steroidal anti-inflammatory drugs, namely ketoprofen, naproxen and flurbiprofen. UiO-66 was immobilized onto the surface of cotton by a polydopamine-functionalized method. The resultant cotton@PDA@UiO-66 was characterized by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The solid phase microextraction conditions were optimized, including sampling flow rate, formic acid content of the eluent, pH value of sample solution, NaCl content and sample volume. By combining with HPLC, this method showed high extraction efficiency (the enrichment factors of ketoprofen, naproxen and flurbiprofen were 44, 49 and 45, respectively), wide linear range (0.1-500 ng/mL), good linearity with R ≥ 0.9996 and satisfactory sensitivity (LODs ≤ 0.03 ng/mL, LOQs ≤ 0.1 ng/mL), as well as good reproducibility (RSD ≤ 4.51%). This method was also successfully applied to extraction of NSAIDs in swine muscle sample. Good recoveries were obtained, ranging from 88.54% to 95.7% with relative standard deviations less than 3.77%.
       
  • Development and validation of a pneumatic model for the reversed-flow
           differential flow modulator for comprehensive two-dimensional gas
           chromatography
    • Abstract: Publication date: Available online 15 September 2018Source: Journal of Chromatography AAuthor(s): Matthew Giardina, James D. McCurry, Pascal Cardinael, Gaëlle Semard-Jousset, Chiara Cordero, Carlo BicchiAbstractThe development of the reversed fill/flush modulator represents a significant advancement in flow-modulated, comprehensive two-dimensional gas chromatography (GC × GC). Compared to the forward flush/fill modulator, the reversed-flow modulator is less susceptible to baseline anomalies and peak tailing as a result of modulator channel overfilling or insufficient purging of high concentration analytes. Flow reversal requires the addition of a bleed capillary not present in the forward-flow modulator. Selecting the appropriate restriction of the bleed capillary is critical. If the bleed capillary is too restrictive, eluate from the first-dimension column can split between the modulator channel and second-dimension column, which also results in baseline artifacts. To gain a better understanding of the reversed-flow modulator, a comprehensive pneumatic model was developed. The model was validated by comparing calculated and measured hold-up times. The errors in calculated hold-up times were less than 1 % of the measured values. The model can be used to predict first-dimension eluate splitting and determine the optimal bleed capillary dimensions to prevent its occurrence. Calculation of the modulator hold-up time can be used to determine the maximum collection time to ensure comprehensive analysis and optimal flush times for partial fill operation.
       
  • The Development of an Automated CounterCurrent Chromatography Process for
           Isolation of Anthocyanins
    • Abstract: Publication date: Available online 14 September 2018Source: Journal of Chromatography AAuthor(s): David Thornton, Linda Barton, Leo HsuAbstractWe developed an automated countercurrent chromatography (CCC) process to isolate anthocyanins from black currant extract utilizing a solvent system of methyl-t-butyl ether, n-butanol, acetonitrile and water with pH adjusted by addition of trifluoroacetic acid in normal phase mode. The process has excellent repeatability as indicated by the high purity of isolated products (90% or better) and the low retention time variability (
       
  • Column selection for comprehensive two-dimensional liquid chromatography
           using the hydrophobic subtraction model
    • Abstract: Publication date: Available online 13 September 2018Source: Journal of Chromatography AAuthor(s): Rebecca K. Lindsey, Becky L. Eggimann, Dwight R. Stoll, Peter W. Carr, Mark R. Schure, J. Ilja SiepmannAbstractTwo-dimensional (2D) liquid chromatography (2DLC) methods have grown in popularity due to their enhanced peak capacity that allows for resolving complex samples. Given the large number of commercially available column types, one of the major challenges in implementing 2DLC methods is the selection of suitable column pairs. Column selection is typically informed by chemical intuition with subsequent experimental optimization. In this work a computational screening method for 2DLC is proposed whereby virtual 2D chromatograms are calculated utilizing the Snyder–Dolan hydrophobic subtraction model (HSM) for reversed-phase column selectivity. Towards this end, 319 225 column pairs resulting from the combination of 565 columns and 100 sets of 1 000 diverse analytes are examined. Compared to other screening approaches, the present method is highly predictive for column pairs that are able to resolve the largest number of analytes. This approach shows a strong sensitivity to the choice of the second dimension column (having a shorter operating time) and a preference for those with embedded polar moieties, whereas a relatively weak preference for C18 and phenyl columns is found for the first dimension.
       
  • On our way to sub-second separations of enantiomers in high-performance
           liquid chromatography
    • Abstract: Publication date: 19 October 2018Source: Journal of Chromatography A, Volume 1572Author(s): Nana Khundadze, Salome Pantsulaia, Chiara Fanali, Tivadar Farkas, Bezhan ChankvetadzeAbstractIn this study our preliminary attempt for obtaining fast and highly efficient separations of enantiomers in high-performance liquid chromatography with slightly modified state-of-the-art commercial instrumentation is described. In order to reach this goal after careful selection of chiral analytes, the preparation of chiral stationary phase (CSP), mobile phase composition and column dimensions were optimized. The concept of segmented chiral-achiral column was introduced. As the result of these optimizations baseline separation of enantiomers was achieved with the analysis time between 1–2 s.
       
  • Selective recognition and fast enrichment of anthocyanins by dummy
           molecularly imprinted magnetic nanoparticles
    • Abstract: Publication date: 19 October 2018Source: Journal of Chromatography A, Volume 1572Author(s): Qian-Yu Zhao, Hai-Tian Zhao, Xin Yang, Hua Zhang, Ai-Jun Dong, Jing Wang, Bin LiAbstractIn this work, a novel synthetic strategy for separation media which quickly specific recognize anthocyanins was developed by dummy molecular imprinting technology and magnetic separation technology. Rutin, similar to cyanidin-3-O-rutinoside structure, was selected as a virtual template. The appropriate molecular imprinting system was selected by NIP library screening method, 4-vinyl pyridine and acetonitrile as functional monomer and solvent respectively. The molecularly imprinted layer was formed on the surface of the magnetic carrier to prepare dummy magnetic molecularly imprinted polymers. The microstructures of prepared composites were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA) and X-ray diffraction (XRD). Adsorption kinetics, isothermal adsorption curves and selective specificity were investigated to further reveal the specific recognition mechanism of the adsorbents on anthocyanins. The dummy molecularly imprinted polymers showed a short kinetic equilibrium time, high selectivity (comparing with quercetin and naringin), and satisfying adsorption capacity for anthocyanins. The binding capacity and the imprinting factor of dummy molecularly imprinted polymers can reach 15.69 mg g−1 and 2.05, respectively. In addition, the purity of cyanidin-3-O-rutinoside in the crude extract from Lonicera caerulea increased to 89% after the adsorption of dummy magnetic molecular imprinted polymers. Many favorable capabilities of the prepared molecularly imprinted polymers also provided the basis for further application for separation and purification of anthocyanins in the future.
       
  • A headspace sorptive extraction method with magnetic mesoporous titanium
           dioxide@covalent organic frameworks composite coating for selective
           determination of trace polychlorinated biphenyls in soils
    • Abstract: Publication date: 19 October 2018Source: Journal of Chromatography A, Volume 1572Author(s): Qiqin Wang, Huihui Wu, Fangying Lv, Yuting Cao, You Zhou, Ning GanAbstractIt’s crucial to develop some simple, selective and rapid extraction pretreatments for detection of trace polychlorinated biphenyls (PCBs) residues in soils. Herein, a new magnetic mesoporous titanium dioxide@covalent organic frameworks (Fe3O4@mTiO2@COFs) composite coating was fabricated and adsorbed onto a Nd-Fe-B magnet for headspace sorptive extraction (HSSE) of seven indicative PCBs (PCB28, PCB52, PCB101, PCB118, PCB138, PCB153 and PCB180) in soils. The coating was assembled layer by layer using hydrothermal method. After being extracted by the magnetic stir bar, the adsorbed PCBs can be desorbed in thermal desorption unit (TDU) and measured by gas chromatography-mass spectrometry (GCMS). Under the optimal conditions, the limit of detection (S/N = 3) was measured less than 0.06 ng/g and the linear range was from 0.01 to 100 ng/g. The new coating exhibited good extraction capacity (its saturated adsorption amount was found to be 35 mg/g), selectivity and can be reused for at least 80 times with a recovery above 90%. The HSSE assay showed the following distinctive advantages: Firstly, the outer COFs coating has a uniform size of cavities (about 3.9 nm), thus PCBs (less than 2 nm) can freely pass through them, while the larger macromolecules can be effectively excluded. Secondly, the inner flower-like mTiO2 coating has good affinity towards chlorine-containing organic compounds, which further improves the selectivity for PCBs. Thirdly, both mTiO2 and COFs have large specific surface area. The synergistic effects of the composite coating make the HSSE assay exhibit high capacity, selectivity and prominent sensitivity towards PCBs detection coupling with TDGCMS. Finally, it is an environmentally friendly pretreatment method that does not require any organic solvents.
       
  • High-throughput analytical method for 265 pesticides and environmental
           contaminants in meats and poultry by fast low pressure gas chromatography
           and ultrahigh-performance liquid chromatography tandem mass spectrometry
    • Abstract: Publication date: 19 October 2018Source: Journal of Chromatography A, Volume 1572Author(s): Yelena SapozhnikovaAbstractA high throughput method for simultaneous determination of 200 pesticides and 65 environmental contaminants: polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs) and other flame retardants, was developed and validated in cattle, swine and poultry muscle tissues. The method was based on sample preparation with QuEChERS extraction followed by an automated robotic sample cleanup with solid phase extraction (SPE) mini-columns using Instrument Top Sample Preparation (ITSP). The automated robotic ITSP was integrated with instrumental analysis (low pressure (LP)GC–MS/MS) to conduct sample cleanup and analysis in parallel. Another aliquot of the initial QuEChERS extract was subjected to UHPLC-MS/MS analysis, and 53 overlapping pesticides were analyzed by both LPGC- and UHPLC-MS/MS (10 min each). Fit-for-purpose LOQs
       
  • Chromatographic enantioseparation of chiral sulfinamide derivatives on
           polysaccharide-based chiral stationary phases
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Qingle Zeng, Quan Wen, Yao Xiang, Lei ZhangAbstractChiral sulfinamides are increasingly recognizedfor their extensive potential applications in chemistry, medicine and material science, yet chromatographic study on these compounds is seldom. In this article, we describe the enantioseparation of twelve closely related chiral sulfinamide derivatives on polysaccharide-based chiral stationary phases (CSPs). We investigated the factors affecting separation, such as the types of chiral columns, the concentration of polar alcohol and the column temperature. The acyclic sulfinamide derivatives—with the exception of a cyclic sulfinamide compound—were effectively resolved with a Chiralcel OD-H column and a mixture of n-hexane:isopropyl alcohol (90:10) as the mobile phase. All compounds except N-benzylidene-2-methylpropane-2-sulfinamide are baseline resolved on the Chiralpak AD-H column, but only eight compounds are resolved on a Chiralpak AS-H column under the given chromatographic conditions. This study offers valuable guidance for future chiral HPLC studies related to chiral sulfinamides.
       
  • Separation of terbutaline enantiomers in capillary electrophoresis with
           cyclodextrin-type chiral selectors and investigation of structure of
           selector-selectand complexes
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Ann Gogolashvili, Elene Tatunashvili, Lali Chankvetadze, Tamas Sohajda, Julianna Szeman, Mehmet Gumustas, Sibel A. Ozkan, Antonio Salgado, Bezhan ChankvetadzeAbstractThe affinity pattern of terbutaline enantiomers towards various cyclodextrins was studied using capillary electrophoresis. The affinity pattern of terbutaline enantiomers was the same towards all studied cyclodextrins except heptakis(2-O-methyl-3,6-di-O-sulfo)-β-CD. Nuclear magnetic resonance spectroscopy was used for understanding of fine structural mechanisms of interactions of β-cyclodextrin and its two sulfated derivatives with the enantiomers of terbutaline. The structure of terbutaline complexes with all 3 cyclodextrins studied was different from each other. In confirmation with our earlier studies it was shown again that capillary electrophoresis represents very sensitive technique for studies of affinity patterns in cyclodextrin complexes with chiral guests. Other instrumental (e.g. NMR spectroscopy and X-ray diffraction analysis) and theoretical techniques, although very useful for obtaining the information regarding the stoichiometry, binding constants and structure of intermolecular complexes, as well as about the forces involved in selector-selectand binding and chiral recognition, may sometimes fail to properly sense those fine differences in the affinity patterns. Therefore, it is recommended to use capillary electrophoresis in order to examine correctness of affinity pattern determined for intermolecular complexes of cyclodextrins with guest molecules by other instrumental or computation techniques.
       
  • Influence of organic modifier and separation modes for lipophilicity
           assessment of drugs using thin layer chromatography indices
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Nejal M. Bhatt, Vijay D. Chavada, Mallika Sanyal, Pranav S. ShrivastavAbstractLipophilicity constitutes one of the most important physicochemical properties in the design and development of drug molecules. In the present work thin layer chromatography (TLC) has been utilized to evaluate lipophilicity of 11 representative drugs, which included six proton pump inhibitors (omeprazole, pantoprazole, rabeprazole, lansoprazole, ilaprazole, and tenatoprazole), an anti-vertigo drug, betahistine, nonsteroidal anti-inflammatory drug, ibuprofen, anti-malarial drug, atovaquone, an anti-HIV agent, atazanavir and a hormonal drug, calcitriol. Normal as well as reversed-phase separation modes were evaluated to study the effect of different organic modifiers for the estimation of lipophilicity. The quantitative descriptor of lipophilicity, the partition coefficient (logP) was estimated by suitably optimizing the solvent systems for both the modes. The best mobile phase pairs for NPTLC and RPTLC were toluene-acetonitrile and water-methanol respectively. Principal component analysis, hierarchical cluster analysis, as well as non-parametric methods like sum of ranking differences and generalized pair wise correlation revealed the dominant pattern in the data. The results obtained from both the separation modes were comparable and were in good agreement with the computational data for all the drugs.
       
  • Direct screening of malonylginsenosides from nine Ginseng extracts by an
           untargeted profiling strategy incorporating in-source collision-induced
           dissociation, mass tag, and neutral loss scan on a hybrid linear
           ion-trap/Orbitrap mass spectrometer coupled to ultra-high performance
           liquid chromatography
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Xiaojian Shi, Wenzhi Yang, Yong Huang, Jinjun Hou, Shi Qiu, Changliang Yao, Zijin Feng, Wenlong Wei, Wanying Wu, Dean GuoAbstractSpecific analytical approaches that enable untargeted profiling of modified metabolites are in great need. An untargeted profiling strategy, by integrating in-source collision-induced dissociation (ISCID)-MS1, mass tag-MS2, and neutral loss scan-MS3, is established on a linear ion-trap/Orbitrap mass spectrometer coupled to ultra-high performance liquid chromatography. This strategy is applied to screen malonylginsenosides from three reputable Panax species (P. ginseng, P. quinquefolius, and P. notoginseng). In light of the preferred neutral elimination of CO2 and entire malonyl substituent (C3H2O3) in the negative electrospray ionization mode, a pseudo-neutral loss scan (PNL) method was established by applying ISCID energy 40 V in MS1, mass tag 43.9898 Da oriented CID-MS2 at normalized collision energy (NCE) 30%, and neutral loss 43.9898 Da-triggered high-energy C-trap dissociation-MS3 at NCE 70%. The PNL approach achieved a high coverage of targeted malonylginsenosides but introduced less false positives. It displayed comparable performance to a precursor ions list-driven targeted approach we have reported in the profiling and characterization of malonylginsenosides, but could avoid complex data processing. Totally 178 malonylginsenosides were characterized from the roots, leaves, and flower buds of P. ginseng, P. quinquefolius, and P. notoginseng, and most of them possess potentially new structures. The compositions of malonylginsenosides identified from these three Panax species are similar, and only malonylginsenoside Rb2 and some minor may have potential chemotaxonomic significance. In conclusion, we provide a potent analytical strategy for the direct and efficient screening of modified metabolites, which may have broad applications in the fields of metabolomics, drug metabolism, and natural product research.
       
  • Size-exclusion chromatography using reverse-phase columns for protein
           separation
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Tung-Yung Huang, Lang-Ming Chi, Kun-Yi ChienAbstractReverse-phase (RP) liquid chromatography (RPLC) and size-exclusion chromatography (SEC) are methods commonly used for protein/peptide separation, and they are based on distinct principles. This study develops a method using RP columns for size-based separation of protein mixtures. Results show that high concentrations of acetonitrile with trifluoroacetic acid as an acid modifier successfully suppressed interactions between proteins and the stationary phase and allowed the RP column to act as a SEC column to separate proteins based on their molecular weight. The reduction of protein disulfide bonds resulted in an improved correlation between the retention time and molecular weight in the RP-based SEC, which indicates that conformation-dependent SEC retention is less important for disulfide-reduced proteins using a current mobile phase. Importantly, the employed salt-free mobile phase allowed the RP-based SEC system to be directly coupled with online mass spectrometry (MS) analysis. Furthermore, by reducing the flow rate and increasing the column length, the separation efficiency was further improved and no adverse effects due to the prolonged separation were observed, which indicates the potential of this strategy to serve as a first-dimensional separation method for constructing an online multi-dimensional LC system. The size-based separation phenomenon with RP columns was further evaluated using a complex protein mixture (a cell lysate), and compared to conventional SEC, more proteins of the cell lysate were observed following the SEC separation principle, which implies the better generality of usage of the RP-based SEC method for protein separation. In summary, results show that the RP-based SEC is highly efficient in achieving protein fractionation. In addition, the employed salt-free mobile phase provides excellent compatibility of the RP-based SEC with other separation strategies or online mass spectrometric analysis. We anticipate that laboratories using RP-HPLC for protein separation will easily be able to move to the size-based separation mode using the same RP-HPLC system.
       
  • Comparison of cation-exchange capillary columns used for ion
           chromatographic separation of biogenic amines
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Yan Li, Pavel N. Nesterenko, Roger Stanley, Brett Paull, Mirek MackaAbstractThe selectivity for 15 biogenic amines and amino acids shown by three capillary cation-exchange columns, IonPac CS19, CS12A and CS17 (250 × 0.4 mm ID, all from Thermo Fisher Scientific), exhibiting medium, medium low and ultra-low hydrophobicity, and either carboxylic or mixed carboxylic/phosphonic acid functional groups, was investigated. A mixed mode retention mechanism was revealed with ion-exchange, hydrophobic and hydrogen bonding interactions contributing to retention of polar organic molecules on these phases. The relative impact of these interactions was evaluated via the effect of concentration and pH of the eluent (methanesulfonic acid) on the retention of fifteen structurally similar biogenic amines and amino acids. Strong hydrogen bonding interactions were observed between the solute amino acid carboxylic groups and cation-exchange groups from the ion-exchangers. This is the first time retention data correlated with logP data has revealed clustering of the solutes in two groups, according to the presence or absence of a carboxylic acid functional group. In addition, stronger retention behaviour was found for the IonPac CS12A cation-exchanger, containing both carboxylic and phosphonic functional groups. Further assessment of the orthogonality plots of retention factors for the three stationary phases revealed that the columns exhibited different complimentary selectivity that can be utilised to achieve specific separations.
       
  • Investigating hydrophilic and electrostatic properties of surfactants
           using retention on two mixed-mode liquid chromatographic columns
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): J. Hammer, J.J.-H. Haftka, P. Scherpenisse, J.L.M. Hermens, P. de VoogtAbstractIn environmental risk assessment, it is essential to understand the relationship between molecular structure and fate and toxicity of organic contaminants. For surfactants, physico-chemical parameters which can reflect the interactions that determine surfactant behavior are not well defined and are therefore needed for the development of robust quantitative structure-activity relationships (QSAR). For the present study, we have measured HPLC retention times of several hydrocarbon and perfluorocarbon surfactant groups on a mixed-mode weak anion-exchange (WAX) and mixed-mode hydrophilic interaction liquid chromatography (HILIC) stationary phase. The nonionic alcohol ethoxylates are well retained on the HILIC column. Retention of anionic surfactants on the HILIC column is likely influenced by the degree of hydration of the surfactants and electrostatic repulsion from silanol groups. Less hydrated anionic surfactants (perfluoroalkyl carboxylates, perfluoroalkyl sulfonates and alkyl sulfates) show minimal hydrophilic interaction while other better hydrated anionic surfactants (alkyl carboxylates and alkyl sulfonates) are well retained. The retention mechanism of surfactants on both columns seems to be related to their degree of hydration, albeit expressed in different retention behavior: generally, retention on the WAX phase increases when retention on the HILIC phase decreases, and vice versa. The retention times from both columns were used to calculate retention factors (k’) and these were subsequently used in calculating parameters that reflect the electrostatic property (kAX) and hydrophilic property (kHILIC) that determine the interaction between the hydrophilic part of the surfactant and the stationary phase. In further development of predictive models, we suggest the use of kAX for anionic surfactants and kHILIC for nonionic surfactants.
       
  • Chasing the elusive hold-up time from an LFER approach
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Xavier Subirats, Althea Justicia, Martí RosésAbstractA homologous series approach derived from the Abraham’s solvation model was developed for the determination of hold-up times. Firstly, it was tested from reversed-phase liquid chromatography data obtained in the literature involving several series of homologues, followed by its application in a polymeric zwitterionic HILIC column using two different homologous series (n-alkyl benzenes and n-alkyl phenones). Acetonitrile and methanol were selected as organic modifiers in a composition range between 80% and 100% in volume. Results obtained for both series were consistent, and hold-up times were found to be strongly dependent on the water content and the organic modifier nature of the mobile phase.
       
  • Preparation and evaluation of a reversed-phase/hydrophilic
           interaction/ion-exchange mixed-mode chromatographic stationary phase
           functionalized with dopamine-based dendrimers
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Di Zhou, Jing Zeng, Qifeng Fu, Die Gao, Kailian Zhang, Xiujun Ren, Kai Zhou, Zhining Xia, Lujun WangAbstractIn this work, a novel dendritic stationary phase was synthesized by the repeated grafting of 1,4-butanediol diglycidyl ether (BDDE) and dopamine (DA) on the surface of silica for performing mixed-mode high-performance liquid chromatography (MHPLC). Elemental analysis (EA), thermogravimetric analysis (TGA) and Fourier transform infrared spectrometry (FT-IR) showed the successful preparation of the dendritic stationary phase. The prepared stationary phase showed the retention mechanisms of reversed-phase liquid chromatography (RPLC), hydrophilic interaction chromatography (HILIC) and ion-exchange chromatography (IEC) under different mobile phase conditions. In detail, alkylbenzenes, polycyclic aromatic hydrocarbons (PAHs) and hydrophobic positional isomers were separated successfully in the RPLC mode. The baseline separation of nucleobases, nucleosides and flavonoids was achieved under HILIC mode, respectively. Meanwhile, some acidic and basic analytes were used to evaluate the IEC mode. The effects of different chromatographic conditions, such as acetonitrile content, salt concentration and pH in the mobile phase, on the different chromatographic modes were also investigated. In addition, the application of the mixed-mode dendritic stationary phase was demonstrated by the analysis of traditional Chinese medicine (TCM), including Carthamus tinctorius L. and Abelmoschus manihot (Linn.) Medicus. Interestingly, the stationary phase also has the ability for the capture and separation of boric acids. These meaningful applications confirmed that the mixed-mode dendritic stationary phase can be potentially applied in the analysis of complex samples.
       
  • Isolation and identification of four major impurities in capreomycin
           sulfate
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Guozhu Liu, Baolei Luan, Guiting Liang, Libo Xing, Liang Huang, Changyun Wang, Ying XuAbstractCapreomycin has good clinical utility to treat multidrug resistant tuberculosis, but it is only used as a second line drug due to its adverse reactions. Literature has demonstrated that the toxicity of capreomycin product is significantly influenced by the impurities in it. Unfortunately, so far, no one impurity in capreomycin has ever been isolated and definitely identified due to its extremely strong basic character and high polarity. An ion-pair method reported in literature can provide separation of capreomycin and its impurities, but it is hard to be used for the preparative purpose. In this study, this ion-pair method was further improved to detect more impurities in capreomycin sulfate substance. Besides the four main components (IA, IB, IIA and IIB), four impurities (impurity A–D) with their contents much higher than the identification threshold were observed. Furthermore, a two dimensional (2D) LC quadrupole-time of flight (Q-TOF) MS method was established to realize high resolution MS analysis of these impurities. For the purpose of preparative isolation, a hydrophilic interaction chromatography (HILIC) method was established. The four main components were well isolated, but unfortunately, the four impurities were co-eluted with each other or with IB by the HILIC method. Fortunately, the degradation experiments revealed that IA and IB could yield clean impurity A and B respectively in acidic medium, and can yield clean impurity D and C respectively in alkaline medium. Therefore, IA and IB were first isolated by the preparative HILIC method, then pure IA and IB underwent acid degradation and base degradation separately and followed by re-isolation by the HILIC method to obtain pure impurity A–D respectively. Based on Q-TOF MS and NMR analysis, the structures (including absolute configuration) of the four isolated impurities were definitely identified.
       
  • High-performance liquid chromatographic determination of
           2-aminoethylphosphonic acid and 2-amino-3-phosphonopropionic acid in
           seawater matrix using precolumn fluorescence derivatization with
           o-phthalaldehyde-ethanethiol
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Shu Wang, Yao Deng, Baomin Liu, Xiaolin Li, Xin Lin, Dongxing Yuan, Jian MaAbstract2-Aminoethylphosphonic acid (2-AEP) and 2-amino-3-phosphonopropionic acid (2-AP3) are two types of abundant and ubiquitous naturally occurring phosphonates used as sources of phosphorus by many prokaryotic lineages. The potential utilization mechanism of 2-AEP and 2-AP3 in eukaryotic phytoplankton is currently under investigation. However, the lack of suitable analytical methods in saline samples are the limitation of such researches. Herein, a high-performance liquid chromatography (HPLC) method for monitoring 2-AEP and 2-AP3 using precolumn fluorescence derivatization with o-phthalaldehyde-ethanethiol (OPA-ET) in seawater matrix was developed. The derivatization procedure and HPLC conditions were carefully examined, which included optimization of the fluorescence excitation and emission wavelengths, the ammonium acetate concentration and pH of the mobile phase, the OPA-ET reagent content and composition and derivatization time. Because increasing salinity was observed to lower the derivatization efficiency, working standards were freshly prepared in artificial seawater with the same salinity as that of the samples for the quantification of 2-AEP and 2-AP3. The developed HPLC method showed a wide linear response with high linearity (R2 > 0.999) and high repeatability at three concentration levels. The relative standard deviation was less than 4.1% for 2-AEP and less than 1.7% for 2-AP3 (n = 7). The limits of detection for 2-AEP and 2-AP3 in artificial seawater matrix were both 12.0 μg/L. The recoveries were 83.0–104% for 2-AEP and 72.6–98.6% for 2-AP3 in different aqueous samples, including algal culture medium prepared with filtered seawater. These results indicated the matrix effect of this method was insignificant.
       
  • A strategy for absolute quantitation of isomers using high performance
           liquid chromatography-ion mobility mass spectrometry and material balance
           principle
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Rui Wang, Wen Gao, Bin Li, Chang-Jiang-Sheng Lai, Shan Lin, Ping Li, Hua YangAbstractAccurate characterization of isomers is a quite challenge and time-consuming work. A major bottleneck is the lack of relevant reference standards. In this work, we conducted a proof-of-concept study to develop a standard-free method for absolute quantitation of isomers by using high performance liquid chromatography-ion mobility mass spectrometry and material balance principle. The isomer structures were characterized by matching the rank order of experimental collision cross sections (CCSs) to that of theoretical CCSs. Then a time-dependent hydrolysis protocol derived from material balance equation was used for the calculation of the relative correction factor (F). Finally, the multi-level normalized matrix approach was developed to absolutely and precisely quantitate isomeric compounds. To assess this method, quercetin-liver microsome reaction pool was applied. With the developed method, four isomeric metabolites of quercetin were accurately analyzed, and metabolic profiling of quercetin isomeric metabolites was firstly reported with the absolute quantitation results. This is an accurate yet simple method for the absolute quantitation of positional isomers of interest.
       
  • Application of cellulose 3,5-dichlorophenylcarbamate covalently
           immobilized on superficially porous silica for the separation of
           enantiomers in high-performance liquid chromatography
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Lia Bezhitashvili, Anna Bardavelidze, Antonina Mskhiladze, Mehmet Gumustas, Sibel A. Ozkan, Alessandro Volonterio, Tivadar Farkas, Bezhan ChankvetadzeAbstractOur earlier studies have demonstrated the applicability of polysaccharide-based chiral selectors in combination with superficially porous (or core-shell) silica (SPS) particles for the preparation of highly efficient chiral stationary phases (CSP). In earlier studies, CSPs were prepared by coating (adsorption) of the chiral selector onto the surface of silica. In this study we report for the first time the CSP obtained by covalent immobilization of a chiral selector onto the surface of SPS particles. The applicability of this CSP for the separation of enantiomers in pure methanol and acetonitrile, as well as in n-hexane/2-propanol mobile phases is shown. The effect of the injected sample amount, mobile phase flow rate and detection frequency on separation performance were studied, as well as high efficiency separation of enantiomers with the analysis time less than 30 s was attempted.
       
  • Apparent efficiency of serially coupled columns in isocratic and gradient
           elution modes
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Szabolcs Fekete, Santiago Codesido, Serge Rudaz, Davy Guillarme, Krisztián HorváthAbstractThe goal of this work was to understand the variation of apparent efficiency when serially coupling columns with identical stationary phase chemistries, but with differences in their kinetic performance. For this purpose, a mathematical treatment was developed both for isocratic and gradient modes to assess the change in plate numbers and peak widths when coupling arbitrary several columns. To validate the theory, experiments were also carried out using various mixtures of compounds, on columns packed with different particle sizes, to mimic highly efficient (new, not used) and poorly efficient columns (used one with many injections). Excellent agreement was found between measured and calculated peak widths. The average error in prediction was about 5% (which may be explained by the additional volume of the coupling tubes).In isocratic mode, the plate numbers are not additive when the coupled columns possess different efficiencies, and a limiting plate count value can be calculated depending on the efficiency and length of the individual columns. Theoretical efficiency limit can also be determined assuming one column in the row with infinite efficiency.In gradient elution mode, the columns’ order has a role (non-symmetrical system). When the last column has high enough efficiency, the gradient band compression effect may outperform the competing band broadening caused by dispersive and diffusive processes (peak sharpening). Therefore, in gradient mode, the columns should generally be sequentially placed according to their increasing efficiency.
       
  • Predictive kinetic optimisation of hydrophilic interaction
           chromatography × reversed phase liquid chromatography separations:
           Experimental verification and application to phenolic analysis
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Magriet Muller, Andreas G.J. Tredoux, André de VilliersAbstractMethod development and optimisation for comprehensive two-dimensional liquid chromatography (LC × LC) is complex, since this involves the intricate relationships between a large number of experimental parameters with the aim of achieving three conflicting goals: maximising separation performance (peak capacity), minimising analysis time and minimising dilution. This is especially true for the on-line combination of hydrophilic interaction chromatography (HILIC) and reversed phase LC (RP-LC) due to the relative elution strengths of the mobile phases used in these modes, which has severe implications for the modulation process and dilution.In this study we report a predictive kinetic optimisation tool for on-line HILIC × RP-LC which is based on theoretical relationships between the optimisation goals, the target analyte properties and chromatographic parameters (column dimensions, flow rates, mobile phases, injection volumes, etc.), allowing all chromatographic parameters to vary simultaneously within defined ranges. Experimental restrictions, such as pressure limits, flow rates, etc., are enforced to ensure all results are practically achievable on a given instrumental configuration. A Pareto-optimality approach is then used to obtain optimal sets of experimental conditions, from which the one(s) best satisfying the requirements in terms of time, dilution and/or peak capacity can be chosen. To overcome the challenges associated with mobile phase incompatibility in the coupling of HILIC and RP-LC, splitting of the first dimension HILIC flow, dilution with an aqueous make-up, or a combination of both, were investigated to establish the best approach to minimise total dilution and maximise performance. The validity of the methodology is demonstrated by deriving optimal conditions for the HILIC × RP-LC separation of procyanidins on selected columns and subsequent experimental verification of the performance for the separation of a cocoa extract.
       
  • On-line incubation and real-time detection by ultra-performance liquid
           chromatography-quadrupole time-of-flight mass spectrometry for rapidly
           analyzing metabolites of anthraquinones in rat liver microsomes
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Yang Xu, Qing Wang, Zhihui Yin, Xiaoyan GaoAbstractThe traditional studies on metabolism in liver microsomes were carried out in off-line form. In this paper, a rapid and convenient method for the study of metabolism of substrates in liver microsomes was established by means of ultra-performance liquid chromatography–quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS): on-line incubation and real-time detection of substrates in liver microsomes. The liver microsomal incubation system was placed in a sample chamber at 37 °C. On-line solid phase extraction (SPE) column was used for on-line sample treatment, its function was to enrich the drug prototype and its metabolites with weak polarity, and elute the phosphate in the samples. The incubation samples were analyzed by setting appropriate injection time, liquid phase elution procedure and mass spectrometry acquisition time. The phase I metabolites of anthraquinone compounds, aloe-emodin (A), rhein (R), emodin (E), chrysophanol (CP), physcion (PS) and their glucosides, were analyzed through this method. The results showed that 8 anthraquinone compounds underwent metabolic reactions such as hydrolysis, oxidation, reduction and hydroxylation in liver microsomal incubation system. In addition, a certain degree of mutual transformation of anthraquinones in liver microsomal incubation system was found. The results provide a reference for in vivo metabolism of anthraquinones in rhubarb. On-line incubation and real-time detection is a feasible, convenient and rapid method for the analysis of drug metabolism in vitro.
       
  • Combination of dispersive solid phase extraction and deep eutectic
           solvent–based air–assisted liquid–liquid microextraction followed by
           gas chromatography–mass spectrometry as an efficient analytical method
           for the quantification of some tricyclic antidepressant drugs in
           biological fluids
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Ali Mohebbi, Saeid Yaripour, Mir Ali Farajzadeh, Mohammad Reza Afshar MogaddamAbstractA dispersive solid phase extraction coupled with deep eutectic solvent–based air–assisted liquid–liquid microextraction has been developed and applied to the extraction and preconcentration of some tricyclic antidepressant drugs in the human urine and plasma samples prior to their determination by gas chromatography–mass spectrometry. In this method, a sorbent (C18) is first added into an alkaline aqueous sample and dispersed by vortexing. By this action, the analytes are adsorbed onto the sorbent. Then, the sorbent particles are isolated from the aqueous solution by centrifugation. Afterward, a deep eutectic solvent, prepared from choline chloride and 4–chlorophenol is used to desorb the analytes from the sorbent. Subsequently, the supernatant solution is removed and added into an alkaline deionized water placed into a test tube with a conical bottom. The resulting mixture is rapidly sucked into a glass syringe and then injected into the tube. This procedure is repeated for several times and a cloudy solution consisting of fine droplets of deep eutectic solvent dispersed into the aqueous phase is formed. After centrifuging the obtained cloudy solution, the tiny droplets of the extractant, containing the extracted analytes, settle at the bottom of the tube. Finally, an aliquot of the extractant is taken and injected into the separation system for quantitative analysis. Several significant factors affecting the performance of the proposed method are evaluated and optimized. Under optimum extraction conditions, the method shows low limits of detection in the ranges of 5–10, 8–15 and 32–60 ng L−1 in deionized water, urine, and plasma, respectively. Enrichment factors are observed to be between 325 to 385 in deionized water, 155 to 185 in urine, and 64 to 72 in plasma. Extraction recoveries are in the range of 65–77 (in deionized water), 62–74 (in urine), and 64–72% (in plasma). The relative standard deviations of the proposed method are ≤ 6% for intra– (n = 6) and inter–day (n = 4) precisions at a concentration of 200 ng L–1 of each analyte. Finally, the applicability of the introduced method is investigated by analyzing the selected drugs in different biological fluids. In the proposed method, for the first time, a deep eutectic solvent composed of safe, cheap, and biodegradable compounds was synthesized and used (at μL–level) as an elution and extraction solvent, simultaneously which led to omit the consumption of toxic organic solvents. This represents a significant advantage in the era of green chemistry. In addition, the introduced method is sensitive, simple in operation, rapid, and efficient.
       
  • Self-assembling covalent organic framework functionalized poly
           (styrene-divinyl benzene-glycidylmethacrylate) composite for the rapid
           extraction of non-steroidal anti-inflammatory drugs in wastewater
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Weixia Li, Lin Huang, Dandan Guo, Yonggang Zhao, Yan ZhuThe growing use of non-steroidal anti-inflammatory drugs (NSAIDs) has seriously affected human health and ecosystems, as a result, the World Health Organization (WHO) has regarded them as emerging contaminants. NSAID’s polar nature and trace amount present in wastewater make their extraction and determination challenging in modern analytical science. Therefore, regarding the need, we herein report a rapid, sensitive and selective in-syringe solid-phase extraction (SPE) method coupled with ultrahigh performance liquid chromatography and UV detector for the determination of seven NSAIDs in environmental water samples. Specifically, the NSAIDs in water samples were directly extracted by using synthesized porous covalent organic framework functionalized poly (styrene-divinyl benzene-glycidylmethacrylate) composite (COF@PS-GMA) without further cleanup procedures. The adsorption of NSAIDs on COF@PS-GMA sorbent was investigated by using adsorption isotherms and kinetic studies. Various parameters, including amount of sorbent, pH of the samples, the volume of desorption solvent, and desorption time that were involved in in-syringe SPE were optimized. Under the optimized conditions, good linearity was observed at 0.005–5.0 μg mL−1 with method quantification limits (LOQs) estimated between 0.54–2.74 μg L−1. The recoveries of the seven NSAIDs at the level of 0.5, 5.0 and 20.0 μg L−1 were ranging from 84.3% to 99.6%.Graphical abstractGraphical abstract for this article
       
  • A linear epitope coupled to DsRed provides an affinity ligand for the
           capture of monoclonal antibodies
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): C. Rühl, M. Knödler, P. Opdensteinen, J.F. BuyelAbstractMonoclonal antibodies (mAbs) dominate the market for biopharmaceutical proteins because they provide active and passive immunotherapies for many different diseases. However, for most mAbs, two expensive manufacturing platforms are required. These are mammalian cell cultures for upstream production and Protein A chromatography for product capture during downstream processing. Here we describe a novel affinity ligand based on the fluorescent protein DsRed as a carrier for the linear epitope ELDKWA, which can capture the HIV-neutralizing antibody 2F5. We produced the DsRed-2F5-Epitope (DFE) in transgenic tobacco (Nicotiana tabacum) plants and purified it using a combination of heat treatment and immobilized metal-ion affinity chromatography, resulting in a yield of 24 mg kg−1 at 90% purity. Using a design-of-experiments approach, we coupled up to 15 mg DFE per mL Sepharose. The resulting affinity resin was able to capture 2F5 from the clarified extract of N. benthamiana plants, achieving a purity of 97%, a recovery of>95% and an initial dynamic binding capacity at 10% product breakthrough of 4 mg mL−1 after a contact time of 2 min. The resin capacity declined to 15% of the starting value within 25 cycles when 1.25 M magnesium chloride was used for elution. We confirmed the binding activity of the 2F5 product by surface plasmon resonance spectroscopy. DFE is not yet optimized, and a cost analysis revealed that boosting DFE expression and increasing its capacity by fourfold will make the resin cost-competitive with some Protein A counterparts. The affinity resin can also be exploited to purify idiotype-specific mAbs.
       
  • Enhanced magnetic ionic liquid-based dispersive liquid-liquid
           microextraction of triazines and sulfonamides through a one-pot,
           pH-modulated approach
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Theodoros G. Chatzimitakos, Stephen A. Pierson, Jared L. Anderson, Constantine D. StalikasAbstractIn this study, an enhanced variant of magnetic ionic liquid (MIL)-based dispersive liquid-liquid microextraction is put forward. The procedure combines a water insoluble solid support and the [P66614+][Dy(III)(hfacac)4−] MIL, in a one-pot, pH-modulated procedure for microextraction of triazines (TZs) and sulfonamides (SAs). The solid supporting material was mixed with the MIL to overcome difficulties concerning the weighing of MIL and to control the uniform dispersion of the MIL, rendering the whole extraction procedure more reproducible. The pH-modulation during extraction step makes possible the one-pot extraction of SAs and TZs, from a single sample, in 15 min. Overall, the new analytical method developed enjoys the benefits of sensitivity (limits of quantification: 0.034–0.091 μg L-1) and precision (relative standard deviation: 5.2–8.1%), while good recoveries (i.e., 89–101%) were achieved from lake water and effluent from a municipal wastewater treatment plant. Owing to all of the above, the new procedure can be used to determine the concentrations of SAs and TZs at levels below the maximum residue limits.
       
  • Providing hyper-branched dendrimer conjugated with β-cyclodextrin based
           on magnetic nanoparticles for the separation of methylprednisolone acetate
           
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Nasim Baimani, Parviz Aberoomand Azar, Syed Waqif Husain, Homayon Ahmad Panahi, Ali MehramiziAbstractThis study introduced a developed approach for dendritic β-cyclodextrin (β-CD) in order to obtain high sorption capacity. Synthetic strategy exploits the reactivity between acrylic acid and allyl glycidyl ether for high-yielding assembly via grafting on to the magnetic nanoparticles that are modified using 3-mercaptopropyltrimethoxysilane for various building branches and host–guest molecules of β-CD. The methodology has been applied for the preparation of a series of β-CD conjugated magnetic nanoparticles with dendrimers as a nano-sorbent for the extraction of methylprednisolone acetate. This study allowed us to probe (i) the effects of the dendric-cyclodextrin architecture on the affinity of sorption capacity, (ii) the drug influence between the cyclodextrin core and the polyester dendrimer, and (iii) the result of sorbent formation for using the anti-inflammatory drug as a target guest into the ring of β-CD on biological extraction. It was found that the adsorption behavior could be fitted by the Langmuir adsorption isotherm model. The adsorption capacity of MPA is found to be 12.4 mg g−1 and indicated the homogeneous sites onto polymer grafted magnetite nano-sorbent surface. Our results confirm the high capability of this type of dendrimer-β-CD for drug extraction in biological fluids and pharmaceutical samples. This nano-sorbent assists the magnetic solid phase extraction technique represented in the high extraction yield (up to 97%) for methylprednisolone acetate in biological human fluids and pharmaceutical samples. Moreover, the achieved polymeric nano-sorbent of the reaction combination was facilitated by a magnetic field and reusability was performed without any notable loss in the sorbent activity.
       
  • On-line combining monolith-based in-tube solid phase microextraction and
           high-performance liquid chromatography- fluorescence detection for the
           sensitive monitoring of polycyclic aromatic hydrocarbons in complex
           samples
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Jinling Pang, Dongxing Yuan, Xiaojia HuangAbstractAn automated and sensitive method, consisting of monolith-based in-tube solid-phase microextraction (IT-SPME) coupled with high-performance liquid chromatography-fluorescence detection (HPLC-FLD), was developed for the monitoring of polycyclic aromatic hydrocarbons (PAHs) in water and milk samples. To enrich PAHs, a new poly (9-vinylanthracene-co-ethylene dimethacrylate) monolith was in-situ prepared and used as the adsorbent of IT-SPME. Various parameters affecting the extraction performance were investigated thoroughly. Under the optimal conditions, the synthesized monolith-based IT-SPME could enrich target PAHs effectively through π-π and hydrophobic interactions. Moreover, the developed on-line IT-SPME-HPLC-FLD method displayed satisfactory analytical merits for PAHs. The limits of detection (S/N = 3) for PAHs in water and milk samples were in the ranges of 0.017–0.23 ng/L and 0.10–2.36 ng/L, respectively. The relative standard deviations (RSDs) for intra-day and inter-day precisions with different spiked concentrations were below 9.8% and 11%, respectively. Finally, the proposed method was successfully applied to quantify ultra-trace target PAHs in water and milk samples. Several ng/L level PAHs were detected. Spiked recoveries achieved for water and milk samples were in the ranges of 78.5–118% and 75.5–119%, respectively. The RSDs varied from 0.30% to 10% for all analytes in all samples. In comparison with reported methods for the monitoring of PAHs, the present method exhibits some merits such as high sensitivity, automation of enrichment and determination procedure, low consumptions of sample and organic solvent.
       
  • Detection of pacific ciguatoxins using liquid chromatography coupled to
           either low or high resolution mass spectrometry (LC-MS/MS)
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Manoella Sibat, Christine Herrenknecht, Hélène Taiana Darius, Mélanie Roué, Mireille Chinain, Philipp HessAbstractCiguatera Fish Poisoning (CFP) is primarily caused by consumption of tropical and sub-tropical fish contaminated by Ciguatoxins (CTXs). These lipid-soluble, polyether neurotoxins are produced by dinoflagellates in the genera Gambierdiscus and Fukuyoa. While there is no regulatory level in Europe for CTXs, the European Food Safety Authority (EFSA) adopted the United States guidance level of 0.01 μg P-CTX1B eq.kg−1 of fish. This limit is extremely low and requires significant improvement in the detection of CTXs.In this study, we compared analytical protocols based on liquid chromatography coupled to tandem low or high resolution mass spectrometry (LC-LRMS or HRMS) to find the best conditions for sensitivity and/or selectivity. Different approaches such as LC conditions, ion choice and acquisition modes, were evaluated to detect the Pacific-ciguatoxins (P-CTXs) on a triple quadrupole (API4000 Qtrap, Sciex) or a quadrupole time of flight (QTOF 6550, Agilent Technologies) spectrometer. Moreover, matrix effects were calculated using matrix-matched calibration solutions of P-CTX1B and P-CTX3C prepared in purified fish extract. Subsequently, the method performance was assessed on naturally contaminated samples of seafood and phytoplankton.With LRMS, the ammoniated adduct ion used as a precursor ion showed an advantage for selectivity through confirmatory transitions, without affecting signal-to-noise ratios, and hence limits of detection (LODs). As also reported by some studies in the literature, methanol-based mobile phase gave better selectivity and sensitivity for the detection of P-CTXs. While the LOD for P-CTX1B and P-CTX3C met the EFSA recommendation level when using LRMS, the findings suggested careful evaluation of instrumental parameters for determination of CTXs. LODs were significantly higher for HRMS, which currently results in the need for a significantly higher sample intake. Nevertheless, HRMS allowed for the identification of artefacts and may allow for improved confirmation of the identity of P-CTXs analogues. Consequently, LRMS and HRMS are considered complementary to ensure adequate quantitation and identification of P-CTXs.
       
  • Review on biomimetic affinity chromatography with short peptide ligands
           and its application to protein purification
    • Abstract: Publication date: 12 October 2018Source: Journal of Chromatography A, Volume 1571Author(s): Yu-Ming Fang, Dong-Qiang Lin, Shan-Jing YaoAbstractBiomimetic affinity chromatography with short peptide ligands, as a promising bioseparation technique, has great potential to protein separation and purification, which is based on highly specific biological interactions between specially-designed ligands and target proteins. Generally, short peptide ligands with the chain length ranging from two to nine amino acids could be divided into two types, linear peptide ligands and cyclic peptide ligands. To obtain the desired short peptide ligands, rational design strategies could be applied by knowing the 3-dimensional (3D) information of the receptors or just knowing the surface cavities and the active site of the receptors. Subsequently, several technologies could be used to screen the optimal peptide ligands from the designed peptide ligands, such as combinatorial chemistry, phage display, mRNA display and computer-based screening technology. The screening efficiency is dependent on the different technology for individual target proteins. After screening, the chromatographic resin could be prepared by coupling the optimal short peptide ligand onto a matrix with some spacer arms. The suitable matrix and spacer arms are also important to enhance the ability of the peptide ligand for protein purification. With the advantages of high affinity, high adsorption capacity, structural stability, low immunogenicity and low cost, biomimetic affinity chromatography with short peptides as the functional ligands have shown an extensive development and application potentiality to protein purification. In this review, we focused on the strategies of rational designs and screening for short peptide ligands, and some items on the perpetration of new resins and their applications for protein purification would also be discussed.
       
  • Dealing with overlapped and unaligned chromatographic peaks by
           second-order multivariate calibration for complex sample analysis: Fast
           and green quantification of eight selected preservatives in facial masks
    • Abstract: Publication date: Available online 12 September 2018Source: Journal of Chromatography AAuthor(s): Xiao-Li Yin, Hui-Wen Gu, Ali R. Jalalvand, Ya-Juan Liu, Ying Chen, Tian-Qin PengAbstractThe quantification of preservatives in cosmetics has attracted great attentions for their controversial and widespread use. HPLC is a prevailing method for preservatives determination among various analytical methods. However, it takes long time to fully separate these compounds because of the complexity of cosmetic matrices. In this study, a fast and green HPLC-DAD strategy assisted with second-order multivariate calibration methods based on alternating trilinear decomposition (ATLD) and multivariate curve resolution-alternating least squares (MCR-ALS) was developed for the simultaneous determination of eight selected preservatives in complex facial mask samples. This appealing strategy proved to be a useful tool for eliminating unknown interferences in complex matrices without complete separation, which benefited from the “second-order advantages” and thus made the determination of the eight analytes in facial mask samples shorten to 8.2 min under a fast elution program. In particular, for the first time, we focused on the applicability of ATLD method for modeling of HPLC-DAD data with severe signal overlapping and slight time shifts. The spiked recovery values were in the range of 71.4-124.6%, and the RMSEP and REP values ranged from 0.07-2.4 μg mL-1 and 1.3-14.5%, respectively, indicating that the ATLD method could provide satisfactory prediction. The resolved spectral profiles and concentration values were compared with those obtained by the MCR-ALS method, an excellent tool for modeling of data deviating from trilinearity. Both qualitative and quantitative results from the two methods were consistent with each other, which evidenced the competence of ATLD method in handling HPLC-DAD data with severe signal overlapping and slight time shifts.
       
  • Advances in offline approaches for chemically speciated measurements of
           trace gas-phase organic compounds via adsorbent tubes in an integrated
           sampling-to-analysis system
    • Abstract: Publication date: Available online 10 September 2018Source: Journal of Chromatography AAuthor(s): Roger Sheu, Aurelie Marcotte, Peeyush Khare, Sophia Charan, Jenna C. Ditto, Drew R. GentnerAbstractGas-phase organic compounds across a range of volatilities, including volatile organic compounds (VOCs), are key components of outdoor air, indoor spaces, and a variety of other anthropogenic and biogenic systems. The collection of offline samples on adsorbent-packed tubes for analysis on laboratory instrumentation has been in use for decades, but with limited sensitivities and compound coverage. We present and evaluate our integrated sampling-to-analysis system that enables offline detailed chemical characterization of multi-faceted organic mixtures at trace concentrations. Its capabilities extend across a diverse variety of VOCs with different molecular features, as well as intermediate and semivolatile organic compounds (I/SVOCs). Samples can be collected manually or via automated devices that have been applied in chamber, field, and aircraft platforms. The laboratory instrumentation can be coupled to both a high resolution mass spectrometer (MS) and a traditional quadrupole MS, though performance metrics presented in this study are determined via the traditional MS. We demonstrate capabilities for detailed chemical characterization and routine performance for a wide range of compound functionalities at sub-part per trillion (ppt) concentrations, and as low as
       
  • Application of metal-organic framework MIL-101(Cr) to microextraction in
           packed syringe for determination of triazine herbicides in corn samples by
           liquid chromatography-tandem mass spectrometry
    • Abstract: Publication date: Available online 10 September 2018Source: Journal of Chromatography AAuthor(s): Yanxiao Jiang, Pinyi Ma, Xinpei Li, Huilan Piao, Dan Li, Ying Sun, Xinghua Wang, Daqian SongAbstractIn this work, a metal-organic framework material MIL-101(Cr) was prepared and used as the sorbent for a laboratory-made semi-automated microextraction in packed syringe (MEPS). Six triazine herbicides, including desmetryn, prometon, ametryn, prometryn, atraton, and dipropetryn, that are commonly found in corn samples, were extracted and determined by the MEPS method and high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Key parameters affecting the extraction efficiencies, including type of extraction solvent, type and amount of sorbent, time of ultrasonic extraction and adsorption, and type, volume and flow rate of elution solvent, were investigated. The limits of detection (LODs, S/N = 3) and quantification (LOQs, S/N = 10) for all analytes obtained by the proposed method were in the ranges of 0.01 - 0.12 ng g-1 and 0.04 - 0.35 ng g-1, respectively, which were far lower than that of reported methods. The findings indicated that the proposed semi-automated MEPS method was easy and efficient for the extraction of triazine herbicides in corn samples.
       
  • Dispersive liquid-liquid microextraction based on liquid anion exchanger
           for the direct extraction of inorganic anions
    • Abstract: Publication date: Available online 10 September 2018Source: Journal of Chromatography AAuthor(s): Mohammad Saraji, Hoda GhambariAbstractFor the first time, the possibility of the use of liquid anion exchangers in dispersive liquid-liquid microextraction for the direct extraction of some inorganic anions (nitrite, nitrate, and iodide) was evaluated. In this technique, chloroform containing a liquid anion exchanger (trioctylamine) was used as extractant. The mixture of the extractant and disperser solvent (acetonitrile) was injected into the acidic sample solution. The protonated trioctylamine formed a water-insoluble salt with the inorganic anions (analytes). After the phase separation and stripping of the analytes from the extractant, the analytes were determined by liquid chromatography with UV detection. Various parameters affecting the extraction efficiency were investigated. Under the optimum conditions, broad linear dynamic ranges, with determination coefficients ( r2) higher than 0.998, and enrichment factors between 94 and 244 were obtained. The limits of detection and quantification were in the range of 0.1-0.5 and 0.4-1.7 µg L-1, respectively. Also, the values of intra- and inter-day relative standard deviations were 3.5-5.8% and 5.5-7.8%, respectively. Various real water samples including sea, tap, river, spring and mineral water were analyzed by the method. The method was sensitive, simple, inexpensive and capable of the simultaneous extraction and determination of the selected inorganic anions.
       
  • Development and validation of an ultra performance liquid
           chromatography-quadrupole time of flight-mass spectrometry (in MSE mode)
           method for the quantitative determination of 20 antimicrobial residues in
           edible muscle tissue of European sea bass
    • Abstract: Publication date: Available online 9 September 2018Source: Journal of Chromatography AAuthor(s): Sofia C. Vardali, Victoria F. Samanidou, Yannis P. KotzamanisAbstractA UPLC-QTOF-MS method for the simultaneous determination of 20 veterinary drug residues and metabolites (tetracyclines, quinolones, sulfonamides and diaminopyrimidines) in edible muscle plus skin tissue of European sea bass (Dicentrarchus Labrax) was developed. For the identification of analytes a positive electrospray ionization quadropole time-of flight mass spectrometer operating in MSE mode (UPLC-QTOF-MSE) was used. MSE mode provides high chromatographic resolution and accurate mass measurements in both MS and MS/MS modes simultaneously in a single run. Separation was achieved on a UPLC BEH C18 (50 mm × 2.1 mm, 1.7 μm) column in a gradient elution program of 10 minutes. Examined antibiotics were isolated easily after a simple solid-liquid extraction procedure with acidic acetonitrile (0.1% v/v formic acid) and Na2EDTA 0.1 M. Recovery rates from muscle plus skin tissue ranged from 93.8% to 107.5% for all targeted compounds. The detection limits and the limits of quantification ranged from 2.22 to 15.00 μg/kg, and from 6.67 to 45.46 μg/kg, respectively. The developed method was validated in terms of selectivity, matrix effect, linearity, accuracy, precision, stability and sensitivity, CCα and CCβ according to European Union Decision 2002/657/EC. The proposed method was applied for the analysis of contaminated fish samples after in feed administration of danofloxacin mesylate.
       
  • A Critical Evaluation of the Use of Gas Chromatography- and High
           Performance Liquid Chromatography-Mass Spectrometry Techniques for the
           Analysis of Microbial Metabolites in Human Urine after Consumption of
           Orange Juice
    • Abstract: Publication date: Available online 9 September 2018Source: Journal of Chromatography AAuthor(s): José Luis Ordóñez, Gema Pereira-Caro, Iziar Ludwig, José Manuel Muñoz, María José Ruiz-Moreno, Alan Crozier, José Manuel Moreno-RojasAbstractThe present study compared and validated two analytical methods, HPLC-HRMS, and GC-MS using MSTFA as derivatization agent, for the analysis of microbiota-derived phenolic acids and aromatic compounds accumulating in urine, collected over a 24 hour period after the consumption of 500 mL of orange juice. In addition, purification procedures using SDB-L and HLB solid phase cartridges were compared when HPLC-HRMS technique was used. Both HPLC-HRMS and GC-MS methodologies were successfully validated in terms of specificity, sensitivity, limit of detection and quantification, recovery and matrix effects. HPLC-HRMS, unlike GC-MS, does not require sample derivatization prior to analysis. GC-MS was not suitable for the analysis of phenolic sulfate and glucuronide metabolites because of their lack of volatility. These phase II metabolites could, however, be analysed by HPLC-HRMS which, as a consequence, provided more detailed and complete information on the phenolic compounds derived from microbiota-mediated degradation of orange juice (poly)phenols. Furthermore, the use of SDB-L and HLB cartridges for sample purification prior to HPLC-HRMS analysis is suitable for free phenolics and glucuronide metabolites but not sulfate derivatives. These findings highlight that the use of an inappropriate analytical protocol can adversely affect studies on the bioavailability of dietary (poly)phenols in which microbiota-derived phenolic catabolites play an important role.
       
  • Magnetic solid phase extraction of sulfonamides based on carboxylated
           magnetic graphene oxide nanoparticles in environmental waters
    • Abstract: Publication date: Available online 8 September 2018Source: Journal of Chromatography AAuthor(s): Shiqian Gao, Yutong Guo, Xinyue Li, Xuedong Wang, Junxia Wang, Feiyue Qian, Haidong Gu, Zhanen ZhangAbstractA magnetic nano-adsorbent material was prepared by functionalizing carboxylic group onto the granule surface of magnetic graphene oxide nanoparticles (CMGO), using in-situ co-precipitating method. The surface morphology was characterized by SEM and TEM. The CMGO was selected as the adsorbent for the magnetic solid phase extraction (MSPE) of sulfonamides (SAs) from environmental water samples, and the eluted analytes were determined by ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). A series of experimental parameters were optimized to improve the extraction efficiency such as amount of CMGO, extraction time, pH, ionic strength of the sample solution and desorption conditions. When the pH of water sample was 4.00, the extraction recoveries (ERs) for SAs were over 82.0 % with 15.0 mg CMGO adsorption for 20 min. Under the optimized extraction conditions, linear range was obtained with coefficients of determination (R2)≥0.9983. The limits of detection for this proposed method were in the range of 0.49-1.59 ng/L, and the enrichment factors were 1320-1702 for eight SAs. The newly developed method was successfully applied to the analysis of trace SAs in real-world water samples, which provided satisfactory ERs in the range of 82.0-106.2% with RSDs less than 7.2%. Overall, it shows a great potential for the concentration of trace amine organic pollutions in complex matrices.
       
  • Preparative enantioseparation of synephrine by conventional and
           pH-zone-refining counter-current chromatography
    • Abstract: Publication date: Available online 7 September 2018Source: Journal of Chromatography AAuthor(s): Yang Zhang, Shanshan Wang, Jianguang Luo, Yaolan Lin, Xiao Xu, Chao Han, Lingyi KongAbstractSynephrine, a chiral adrenergic agonist, exists as R- (more active) and S-enantiomers (less active) that are difficult to separate because of their alkalinity and high polarity. Herein, we show that although this enantioseparation can hardly be achieved by high-performance liquid chromatography, acceptable preparative separation can be realized using high-speed counter-current chromatography (HSCCC) and pH-zone-refining counter-current chromatography (CCC) under optimal conditions. Specifically, 23.0 mg of S-synephrine and 25.0 mg of R-synephrine were isolated from 60.0 mg of racemic synephrine by conventional HSCCC, while 70.0 mg of S-synephrine and 69.0 mg of R-synephrine were obtained from 200.0 mg of racemic synephrine by pH-zone-refining CCC. The pH-zone-refining CCC was identified as the most efficient enantioseparation technique for synephrine and can be applied for the preparative enantioseparation of other β-amino alcohols.
       
  • Method development for the certification of a ginsenoside calibration
           solution via liquid chromatography with absorbance and mass spectrometric
           detection
    • Abstract: Publication date: Available online 7 September 2018Source: Journal of Chromatography AAuthor(s): Walter B. Wilson, Lane C. SanderAbstractThe research presented here describes the development of two analytical methods for use in the certification of a ginsenoside calibration solution Standard Reference Material (SRM) 3389 consisting of seven ginsenosides: Rg1, Re, Rf, Rb1, Rc, Rb2, and Rd. The new methods utilized the liquid chromatographic (LC) separation of ginsenoside mixtures with absorbance detection (UV) and mass spectrometry (MS). Ginsenosides Rb3, Rg2, Rg3, Rh1, and Rh2 were evaluated for use as internal standards for LC/MS measurements. The 12 ginsenosides were baseline resolved by gradient elution LC/UV, with an initial mobile phase composition of 22 % acetonitrile and 78 % water, flow rate of 0.7 mL/min, and column temperature of 25 °C. The work presented here includes a detailed investigation into the optimization of the chromatographic conditions to minimize measurement biases that result from unresolved constituents. Temperature and mobile phase composition are known to play a significant role in column selectivity; however, flow rate is expected to influence primarily the separation efficiency and detection sensitivity. In the current study, column selectivity changed with changes in flow rate and the relative retention of ginsenoside Rg2 and Rh1 changed as the flow rate increased from 0.6 mL/min to 1.0 mL/min.
       
  • Electrospun nanofiber cloud for ultrafast solid phase micro-extraction of
           trace organics in water samples
    • Abstract: Publication date: Available online 7 September 2018Source: Journal of Chromatography AAuthor(s): Xiaohui Yan, Yingying Zhan, Dongdong Zhong, Yanshuo Li, Dapeng WuAbstractIn order to achieve ultrafast solid phase micro-extraction (SPME) of trace organics in water samples, the robust polyimide/polyvinylpyrrolidone (PI/PVP) composite nanofiber was prepared by electrospinning. Unlike the nonwoven electrospun membrane bulk widely used for SPME, the hydrophilic PI/PVP nanofibers here can be easily dispersed into and recovered from water sample like a cloud, so nanofiber cloud SPME (NC-SPME) was proposed in this work. The extraction performance of the NC-SPME method was evaluated using phthalates and organochlorine pesticides as model analytes. The extracted analytes were then desorbed by acetone and eventually quantified by gas chromatography-mass spectrometry (GC-MS). The extraction equilibrium was reached in 30 s for most of the phthalates and 2 min for organochlorine pesticides. While for bar-SPME, the equilibrium time was much longer than 2 hours. At the extraction time of 5 min, the recoveries of phthalates and organochlorine pesticides were more than 34% and 52% by the NC-SPME method while they were less than 15% and 10% respectively by the bar-SPME method. In a word, the NC-SPME method presented significant advantages such as fast equilibrium and high recoveries compared to bar-SPME. For the phthalates analysis of real samples by NC-SPME, 5 mL of water sample was used for a 5-min extraction, linear range covered 1-2 orders of magnitude with correlation coefficients (r) higher than 0.99 and limits of detection (LODs) at ng/L levels for all of the tested water samples. This method will be useful for the rapid micro-extraction of other kinds of organics in water samples even biological fluid samples due to the stable composition, ultra-hydrophilic surface of PI/PVP nanofiber, and the biocompatible nature of PVP.
       
  • A gas chromatography full scan high resolution Orbitrap mass spectrometry
           method for separation and characterization of 3-hydroxymethyl pyridine
           ester of fatty acids at low levels
    • Abstract: Publication date: Available online 7 September 2018Source: Journal of Chromatography AAuthor(s): Franck Merlier, Nabila Imatoukene, Stéphane Octave, Jean-Marc Nicaud, Brigitte ThomassetAbstractFatty acid methyl esters (FAMEs), which are commonly used to characterize lipids, have several limitations to conclude on many structures. 3-Pyridylcarbinol esters (3-PCE) are used to characterize fatty acid structures [1], in particular, to identify ring and double bond positions on the carbon chain. Chromatographic separation of these esters is complex due to their polarity and high boiling points. In this study, we used a column with high resolutive power based on ionic liquids to increase the separation quality in gas chromatography (GC). In addition, we used a high-resolution detector (Orbitrap) to limit non-specific signals and improve the detection limits. This detector could be used with a mass filter at 5 ppm for the rapid determination of 3-PCE from its characteristic ions (m/z = 108.0441 and 92.0495). This filter allowed the identification of derivative fatty acids with good sensibility. Thus, it was possible to characterize 3-PCE by measuring the exact fragment masses to confirm structures such as C19:2n12cycloΔ9.
       
  • Estimation of peak capacity based on peak simulation
    • Abstract: Publication date: Available online 7 September 2018Source: Journal of Chromatography AAuthor(s): J.A. Navarro-Huerta, J.R. Torres-Lapasió, M.C. García-Alvarez-CoqueAbstractPeak capacity (PC) is a key concept in chromatographic analysis, nowadays of great importance for characterising complex separations as a criterion to find the most promising conditions. A theoretical expression for PC estimation can be easily deduced in isocratic elution, provided that the column plate count is assumed constant for all analytes. In gradient elution, the complex dependence of peak width with the gradient program implies that an integral equation has to be solved, which is only possible in a limited number of situations. In 2005, Uwe Neue developed a comprehensive theory for the calculation of PC in gradient elution, which is only valid for certain situations: single linear gradients, absence of delays and extra-column effects, Gaussian peaks and constant plate count. Going beyond these limitations implies resolving algebraic expressions that unfortunately cannot be integrated. In this work, PC is predicted for multiple situations based on peak simulation. The approach is more general and can be applied for situations out of the scope of the Neue outline, such as complex multi-linear gradients, including asymmetrical peaks. The plots of PC versus retention time of the last eluted solute give rise to Pareto fronts, and can be useful for the probabilistic enhancement of peak resolution in situations where complex multi-analyte samples are processed.
       
  • Separation of highly charged (+5 to +10) amphipathic α-helical peptide
           standards by cation-exchange and reversed-phase high-performance liquid
           chromatography
    • Abstract: Publication date: Available online 5 September 2018Source: Journal of Chromatography AAuthor(s): Colin T. Mant, Andrew Byars, Sean Ankarlo, Ziqing Jiang, Robert S. HodgesAbstractWe are currently examining the potential of amphipathic cationic α-helical peptides as a new generation of peptide standards for both cation-exchange high-performance liquid chromatography and reversed-phase chromatography. Thus, amphipathic peptides are particularly suitable for high-performance liquid chromatography standards due to the preferred binding of the non-polar face to the hydrophobic stationary phase of reversed-phase packings or the preferred binding of the polar face to the charged/hydrophilic stationary phase of cation-exchange packings. The ability of different reversed-phase or cation-exchange matrices to separate mixtures of peptide standards with only subtle hydrophilicity/hydrophobicity variations in both the non-polar and polar face of the peptides can then be assessed. Currently, we have designed de novo a mixture of six 26-residue all D-conformation amphipathic cationic α-helical peptides with a single, positively charged lysine residue in the center of the non-polar face and an increasing number of lysine residues (4-9 residues) replacing neutral residues in the polar face, resulting in an overall net positive charge of +5 to +10. Thus, the non-polar, preferred reversed-phase chromatography binding face remains constant, with only the polar face varying in hydrophilicity/hydrophobicity. Interestingly, even with the non-polar face remaining constant, reversed-phase columns of varying functional group properties (e.g., C8, C18, phenyl, polar endcapped, polar embedded) and porosity (porous versus superficially porous) were able to separate the six peptides in aq. TFA/acetonitrile gradients, albeit with different selectivities. The value of the standards in cation-exchange chromatography was expressed by monitoring the requirement of acetonitrile (0-40% in the mobile phase) to overcome hydrophobic interactions of the peptides with the cation-exchange matrix matrix when eluting with sodium perchlorate gradients at pH 6.5. Interestingly, the resolution of the higher charged peptides (+8,+9,+10) was particularly sensitive to acetonitrile levels. Our results clearly demonstrate the excellent potential of these novel peptide standards to enable optimal column choice and mobile phase conditions for reversed-phase chromatography and cation-exchange chromatography for peptide separations.
       
  • Determination of glyoxal and methylglyoxal in atmospheric fine particulate
           matter by vortex-assisted micro-solid phase extraction and liquid
           chromatography-diode array detection
    • Abstract: Publication date: Available online 5 September 2018Source: Journal of Chromatography AAuthor(s): Nyi Nyi Naing, Hian Kee LeeAbstractDetermination of α-dicarbonyl compounds, glyoxal (Gly) and methyl glyoxal (Mgly), in atmospheric fine particulate matter PM2.5 (particulate matter with an aerodynamic diameter of less than 2.5 µm) which play vital roles in generating secondary organic aerosols in the ambient air, was carried out by vortex-assisted micro-solid phase extraction (VA-µ-SPE)˗liquid chromatography-diode array detection (LC-DAD), with on-sorbent derivatization by 2,4-dinitrophenylhydrazine (DNPH). This is the first time such an approach of combining on-sorbent derivatization and extraction in one step together with LC analysis has been applied to PM2.5. Extraction parameters such as selection of sorbent, extraction time, desorption time and sample volume were optimized using water samples spiked with Gly and Mgly. Under the most favourable conditions, good intra- (1.39% to 2.78%) and inter-day (2.29% to 6.56%) precision and linearity (ranging between 0.5 and100 ng mL̶ 1) along with coefficients of determination 0.998 and 0.997, were determined. The limits of detection were determined to be 0.14 ng mL-1 (derivatized Gly) and 0.15 ng mL-1 (derivatized Mgly) whereas the limits of quantification were 0.47 ng mL-1 and 0.50 ng mL-1, respectively. The developed method was successfully employed to the determination of Gly and Mgly associated with PM2.5. The latter was collected on glass fiber filters which were immersed in methanol: water (1:1 v/v) for µ-SPE, which was conducted using a sorbent pre-coated with DNPH. The concentrations of the Gly and Mgly were determined to be 0.38 ng m-3 and 0.41 ng m-3 in the sampled ambient air, with relative recoveries of between 69 to 97%.
       
  • Application of quantitative analysis of multi-component system approach
           for determination of ginsenosides in different mass-spectrometric
           conditions
    • Abstract: Publication date: Available online 5 September 2018Source: Journal of Chromatography AAuthor(s): Elena Stekolshchikova, Polina Turova, Oleg Shpigun, Igor Rodin, Andrey StavrianidiAbstractThe lack of standard substances is a bottleneck for quality control in traditional and alternative medicine. Development of the HPLC-UV approaches combined with single standard for quantitative analysis of multi-component system (QAMS) allowed determination of several plant biomarkers by implementation of the relative response factors (RRFs). Robustness and ruggedness of such methods are commonly demonstrated by performing the analysis in changing analytical conditions on the different HPLC equipment and columns. The nature of MS detection is much more complicated and dependent on the instrumentation. Therefore, this study was conducted to justify the use of RRFs for HPLC-MS determination of bioactive compounds from plants. Protopanaxatriol (PPT), protopanaxadiol (PPD) and ocotillol (OT) ginseng saponins (ginsenosides) were successfully separated on a reversed-phase PFP-column with high group selectivity. Fragmentation patterns for these groups of compounds were established on different HPLC-ESI-MS systems and at varied declustering potentials (DPs). The use of sapogenin fragmentation ions in positive detection mode and group reference standards was shown to be an optimal way to perform quantification. The performance of the developed group targeted HPLC-MS-QAMS approach was tested in the course of measurements conducted on the different instrumentation. The differences between QAMS and external standard method (ESM) quantification results were below 15% for all determined saponins.
       
  • Detection and Quantification of Trace Airborne Transfluthrin
           Concentrations via Air Sampling and Thermal Desorption Gas
           Chromatography-Mass Spectrometry
    • Abstract: Publication date: Available online 5 September 2018Source: Journal of Chromatography AAuthor(s): Michael W.C. Kwan, Jason P. Weisenseel, Nicholas Giel, Alexander Bosak, Christopher D. Batich, Bradley J. WillenbergAbstractA rapid thermal desorption-gas chromatography-electron ionization-mass spectrometry (TD-GC-EI-MS) method for airborne transfluthrin detection is studied. Active air sampling of 9 L over 1 h at 23 °C through a Tenax®-loaded tube resulted in efficient capture of airborne transfluthrin. Subsequent thermal desorption was employed to achieve an LOD of 2.6 ppqv (parts per quadrillion by volume). A minimum primary desorption temperature of 300 °C is necessary for optimal recovery of sample from the Tenax® adsorbent. The matrix effects of indoor air lead to an error of 10.9 % and 10.5 % recovery of sample (10 pg and 100 pg loaded tubes, respectively). The linear range was 74-74,000 ppqv with a correlation coefficient of 0.9981. Active air sampling of a novel passive release device revealed a ~150 pg/L airborne concentration gradient over 1 m, providing spatial characterization of the device’s performance. This efficient method allows for the remote collection of samples and rapid analysis of airborne transfluthrin from industrial applications, optimization studies of commercial products as well as domestic/household monitoring.
       
  • Preparation and application of a restricted access material with hybrid
           poly(glycerol mono-methacrylate) and cross-linked bovine serum albumin as
           hydrophilic out layers for directly on-line high performance liquid
           chromatography analysis of enrofloxacin and gatifloxacin in milk samples
    • Abstract: Publication date: Available online 3 September 2018Source: Journal of Chromatography AAuthor(s): Wei Huang, Panpan Wang, Ping Jiang, Xiangchao Dong, Shen LinAbstractA novel restricted access material (RAM) was prepared through combination of hydrophilic polymer poly(glycerol mono-methacrylate) and cross-linking bovine serum albumin (BSA) for direct biological analysis. In the material preparation, the poly(styrene-co-divinylbenzene) and poly(glycerol mono-methacrylate) were grafted on silica successively by atom transfer radical polymerization. Then the BSA was adsorbed on the material and cross-linked through an in-column process. The BSA recoveries of the resulted RAM were higher than 99.3%. Small molecules such as alkylbenzene and quinolone antibiotics could be retained with a reversed phase mechanism. The column packed with RAM had good long term stability and could last at least five months without significantly changed in its efficiencies. An on-line SPE/HPLC method for the analysis of enrofloxacin and gatifloxacin in milk samples was established by using the resulted RAM as the solid-phase extraction material. The detection and quantitation limits of two antibiotics were 8.22 and 27.4 ng mL-1, respectively. In the method validation, least recovery 88.5% with relative standard deviation of less than 3.9% was obtained. It demonstrated that the method is reliable and the material can be used for the direct analysis of veterinary drug residues in biological samples.
       
  • Σpider diagram: A universal and versatile approach for system comparison
           and classification. Part 2: Stationary phase properties
    • Abstract: Publication date: Available online 3 September 2018Source: Journal of Chromatography AAuthor(s): E. Lesellier, C. WestAbstractMany different sorts of bonded phase chemistries may be used in high-performance liquid chromatography (HPLC) in the reversed-phase mode: C8, C18 (type A or B), polar-embedded C18, phenyl, pentafluorophenyl, or cyanopropyl. To assess their retention and selectivity properties, chromatographic tests exist. The data obtained from these tests may be presented in three ways. First, simple classification diagrams may be plotted, when only two or three parameters are studied. Secondly, chemometric treatments such as principal component analyses (PCA) or hierarchical cluster analyses (HCA) may be computed, when at least 4 parameters are studied. These are sometimes uneasy to interpret. Thirdly, the “distance” between one column and a reference column may be estimated, through calculated ranking (F or CDF) or selectivity (s) factors.In this paper, another treatment type is applied to the data of Euerby (Tanaka test) and Snyder (Hydrophobic Subtraction Model), each of these tests having 6 parameters. This treatment produces a visual classification, called spider diagram. In the first part of this series, this type of classification was applied to the classification of solvents. A logical and easily comprehensible classification is obtained for the varied types of bonded phases, with a clear location, which can be related to the chromatographic properties. The comparison of these diagrams shows that the classification based on Snyder’s hydrophobic subtraction model discriminates the stationary phases more effectively than the one based on the Tanaka test.Finally, on the basis of the parameter relevance and in order to favour comparison between these two tests and a third one called the carotenoid test, simplified classification maps are proposed. For Tanaka test, the selected parameters are the pentylbenzene retention factor (hydrophobicity), the benzylamine/phenol separation factor at pH 7.6 (polar surface activity) and the triphenylene/ortho-terphenyl (shape selectivity) separation factor. For Snyder test, the parameters selected are the ethylbenzene retention factor (hydrophobicity) the C term at pH 7.0 (polar surface activity) and the S* term (steric electivity). The location of some stationary phases onto the maps and their rankings are compared and shown to agree well between the three tests.
       
  • Enzyme-assisted extraction and liquid chromatography-inductively coupled
           
    • Abstract: Publication date: Available online 1 September 2018Source: Journal of Chromatography AAuthor(s): Fa Zhao, Yanming Liu, Xiqi Zhang, Rui Dong, Wenjiang Yu, Yanfang Liu, Zhimou Guo, Xinmiao Liang, Jianhua ZhuAbstractA sensitive, simple and rapid method for the simultaneous determination of eleven arsenic species has been developed. A high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) technique was used for the analysis of eleven arsenic species in less than 17 min. Different extraction solutions were explored and the recovery results using water and aqueous acidic solvents, aqueous organic solvents and enzymes showed that 40 mg protease with 0.75 mL 0.5% hydrochloric acid (v/v) as the extraction agent gave the best experimental results. Species separation with ammonium carbonate solution as the mobile phase was conducted on an anion-exchange chromatographic column using gradient elution. The column temperature was 20 °C and kinetic energy discrimination (KED) was employed to eliminate spectral interference. The use of KED mode effectively removed interference from 75ArCl. The detection limit (LD) of the method was in the range of 0.11–0.59 µg kg-1. Repeatability values obtained for spiked real fish samples were in the range of 1.1%–7.6%. Accuracy was calculated based on the analysis of spiked real fish samples at five concentration levels. Obtained recoveries were 91%–106%. The validated method was used in a pilot study to analyze real samples of fish, the organic arsenic especially AsB was the major arsenic specie present in the analyzed samples, only trace amount of inorganic arsenic were detected. The analytical method should improve the assessment of human exposure associated with arsenic intake from fish.
       
  • Gradient extractive phase prepared by controlled rate infusion method: An
           applicable approach in solid phase microextraction for non–targeted
           analysis
    • Abstract: Publication date: Available online 1 September 2018Source: Journal of Chromatography AAuthor(s): Marzieh Enteshari Najafabadi, Elahe Kazemi, Habib BagheriAbstractThe aim of this study is to introduce an extractive phase based on gradient concept by continuous changing in chemical functional groups for non–targeted analysis. For this purpose, three different two–component coatings containing (3–aminopropyl)trimethoxysilane (APTES) as polar and either phenyltriethoxysilane (PTES), octyl–trimethoxysilane (OTMS) or methyltrimethoxysilane (MTMS) as nonpolar precursors were formed on the modified stainless steel wires using controlled rate infusion (CRI) method. The presence of polar and/or non–polar functional groups on the surface of substrate was evaluated by Fourier–transform infrared spectroscopy (FTIR) together with contact angles determined alongside the gradient surface. The morphology and thickness of the prepared fibers were also investigated by scanning electron microscopy (SEM). Furthermore, uniform single–component fibers from polar (APTES) and nonpolar (PTES) coatings were fabricated in order to be compared with the gradient sorbent. The gradient phase was implemented as a fiber coating in headspace– or immersed–solid phase microextraction of various compounds including chlorobenzenes, polycyclic aromatic hydrocarbons, chlorophenols and volatile organic compounds (Log Kow range: -0.77 to 4.64). Under the optimized condition, the limits of detection and quantification were obtained in the range of 0.01–0.5 µg L-1 and 0.05–1.5 µg L-1, respectively. The intra–day and inter–day relative standard deviations of 2–10% and 11–17% were achieved, respectively. The method was successfully applied to the extraction of VOCs from real water sample and relative recoveries were between 89 and 105%. The capability and efficiency of the gradient coating appears to be quite appropriate for non–targeted analysis.
       
  • Improving Visualization of Trace Components for Quantification Using a
           Power Law Based Integration Approach
    • Abstract: Publication date: Available online 1 September 2018Source: Journal of Chromatography AAuthor(s): Garrett Hellinghausen, M. Farooq Wahab, Daniel W. ArmstrongAbstractIn some cases, trace component analysis only requires a sensitive and high-resolution mass spectrometer. However, enantiomers must be completely separated to be differentiated with a mass spectrometer, which is highly dependent on the stationary-mobile phase composition. In case of a challenging chiral separation, instead of trying new columns for screening purpose, resolution enhancement techniques could be used to resolve partially overlapping peaks. A well-known enhancement method is the power law, which increases the linear dynamic range of each analyte and reduces excessive noise. In many cases, the peak noise can decrease significantly by applying the power law. However, the main drawback is that this approach changes relative peak areas and heights of each peak in a non-linear fashion which limits its use for quantitative purposes. In this study, a normalized power law was utilized for extracting correct area information. It is a simple (5 step) protocol that only required Microsoft Excel, and results in enhanced visualization of trace components, especially in low signal/noise environments, and makes integration convenient and reproducible. Several difficult chiral trace component analyses were investigated, including applications pertaining to ultrafast high-throughput chromatography, enantiopurity, and peak purity analysis. For complicated cases with multiple overlapped peaks of different resolutions, a segmented normalized power law was utilized. A trace component coeluting near a dead volume peak and a trace enantiomeric component in the tail of the corresponding enantiomeric peak were virtually enhanced. As an additional tool, first and second derivatives were utilized to identify if an enantiomeric impurity is coeluting with the dominant enantiomer under overload conditions. Idiosyncrasies of the derivative test are discussed. This study shows how these simple approaches can be used for accurate quantitation, specifically for trace enantiomeric components.
       
  • Significant sensitivity enhancement in Hadamard transform high-performance
           liquid chromatography by application of long modulation sequences
           constructed from lower order sequences
    • Abstract: Publication date: Available online 1 September 2018Source: Journal of Chromatography AAuthor(s): Alexander F. Siegle, Sebastian Pallmann, Oliver TrappAbstractHadamard encoding, utilizing pseudo-random injection sequences with n-bit (2n-1) elements, is applied in analytical sciences to enhance the signal-to-noise ratio (S/N) of weak analyte signals. We have developed a software approach that allows using Hadamard encoding on standard HPLC systems. This strategy is only limited by the number of instructions that can be transmitted to the autosampler and its performance degrades if an accumulation of chromatographic irregularities occurs while applying long modulation sequences. Here we demonstrate that such sequences (>4000 elements) can be subdivided into suitable subsequences, which can be independently executed. The measured subchromatograms are subsequently realigned and deconvoluted yielding a chromatogram with increased S/N. This opens an avenue to achieve unprecedented sensitivity gains. In the analysis of highly diluted nucleoside samples an S/N enhancement of up to 30-fold was observed. Furthermore, we applied the method to a sample containing the antibiotic drug fidaxomicin and found a significant sensitivity improvement that strongly depends on the applied elution conditions.
       
  • Miniaturized Micromachined Gas Chromatography with Universal and Selective
           Detectors for Targeted Volatile Compounds Analysis
    • Abstract: Publication date: Available online 1 September 2018Source: Journal of Chromatography AAuthor(s): Ronda Gras, Jim Luong, Robert A. ShellieAbstractAn effective analytical strategy for targeted analysis of volatile organic compounds which combines two orthogonal separation mechanisms and multiple tunable detection in a compact transportable analytical system is introduced. This strategy uses a commercially available micromachined gas chromatograph comprising a micromachined on-board thermal conductivity detector. The chromatograph capability is enhanced by incorporating a modified diode array detector and a radio frequency modulated ion mobility spectrometry microfabricated electromechanical system. The analytical platform offers powerful detection capabilities of individual compounds and various classes of volatile organic compounds with improved provisional confirmatory capability. The transportable micromachined gas chromatograph employs field replaceable conventional capillary columns for the separation of analytes. The use of a silicon micromachined sample introduction device affords fast injection to minimize band broadening with fast chromatographic separation rendered in the order of minutes. Advantaged synergy also includes leveraging the resolving power of gas chromatography to minimize charge exchange in the ionization chamber of the differential mobility spectrometer for improved detector performance. Performance of this scalable and transportable analytical system is demonstrated with relevant volatile compounds such as acetaldehyde, acetone, carbon disulfide, benzene, and ethyl butyrate having a day-to-day variability less than 5% and with a high degree of reliability.
       
  • Coupling a gamma-ray detector with Asymmetrical Flow Field Flow
           Fractionation (AF4): Application to a Drug-Delivery System for
           Alpha-Therapy
    • Abstract: Publication date: Available online 1 September 2018Source: Journal of Chromatography AAuthor(s): Sandrine Huclier-Markai, Alicia Grivaud-Le Du, Estelle N’tsiba, Gilles Montavon, Marie Mougin-Degraef, Jacques BarbetABSTRACTAlpha-particle-emitting radionuclides have been the subject of considerable investigation as cancer therapeutics, since they have the advantages of high potency and specificity. Among α-emitting radionuclides that are medically relevant and currently available, the lead-212/bismuth-212 radionuclide pair could constitute an in vivo generator. Considering its short half-life (T1/2 = 60.6 min), 212Bi can only be delivered using labelled carrier molecules that would rapidly accumulate in the target tumor. To expand the range of applications, an interesting method is to use its longer half-life parent 212Pb (T1/2 = 10.6 h) that decays to 212Bi. The challenge consists in keeping 212Bi bound to the vector after the 212Pb decay. Preclinical and clinical studies have shown that a variety of vectors may be used to target alpha-emitting radionuclides to cancer cells. Nanoparticles, notably liposomes, allow combined targeting options, achieving high specific activities, easier combination of imaging and therapy and development of multimodality therapeutic agents (e.g., radionuclide therapy plus chemotherapy). The aim of this work consists in assessing the in vitro stability of 212Pb/212Bi encapsulation in the liposomes. Indeed, the release of the radionuclide from the carrier molecules might causes toxicity to normal tissues. To reach this goal, Asymmetrical Flow Field-Flow Fractionation (AF4) coupled with a Multi-Angle Light Scattering detector (MALS) was used and coupling with a gamma (γ) ray detector was developed. AF4-MALS-γ was shown to be a powerful tool for monitoring the liposome size together with the incorporation of the high energy alpha emitter. This was successfully extended to assess the stability of 212Bi-radiolabelled liposomes in serum showing that more than 85% of 212Pb/212Bi is retained after 24 h of incubation at 37 °C.
       
  • Ensuring Selectivity using Retention Time Modulation by Solvent
           Composition, applied to the Analysis of Phenol in e-Liquids
    • Abstract: Publication date: Available online 1 September 2018Source: Journal of Chromatography AAuthor(s): A. Auer, R. Kapeller, K. Rothberger, M. SchütteAbstractA gas chromatographic method for the determination of volatile contaminants (halogenated solvents, benzene, toluene, ethyl-benzene, xylenes, styrene) and phenol in e-liquids was developed and validated with a working range of 0.01 (limit of quantification) to 0.5 mg/l, and variation coefficients between 2 and 14 %. Selectivity performing MS/MS-detection was sufficient for all analytes except for phenol: e-liquids contain high amounts of aroma compounds in excess of 105 compared to phenol. A number of these compounds potentially interfere at the retention time of phenol, showing all masses (including daughter ions and transitions) of phenol. To allow the detection of phenol in this matrix, a novel approach of adding a polar molecule to the injection solvent was used, modulating the polarity of the column, and thus the retention time of phenol. By adding 3 µl/ml and 10 µl/ml of 1,2-propanediol the retention time of phenol was shifted by 0.06 and 0.11 min respectively, while interfering peaks have not been shifted. This allowed a reliable confirmation of the presence of phenol. The introduced approach is an easy way to generate an additional chromatographic dimension for confirmation purposes, not requiring additional equipment.
       
  • Numerical and Analytical Investigation of the Possibilities to Enhance the
           Thermal Conductivity of Core-shell Particle Packed Beds
    • Abstract: Publication date: Available online 1 September 2018Source: Journal of Chromatography AAuthor(s): Sander Deridder, Wim Smits, Hamza Benkahla, Ken Broeckhoven, Gert DesmetAbstractWe report on a numerical study of the thermal conductivity of core-shell particle packed bed columns. Covering a variety of packing structures and a broad range of mobile phase and porous zone conductivities, it was in all cases found that switching to particles with a highly conducting core (e.g., with a gold or copper core instead of a silica core) would produce a much smaller increase of the effective heat conductivity of the bed (keff) than previously expected in literature. We found maximal increases on the order of some 20-70%, which is much lower than the potential increases up to 2000% assumed in literature. The overestimation in literature could be attributed to the fact that this literature was based on an incorrect extrapolation of the Zarichnyak-model which was the heat conductivity model predominantly used up till now. On the other hand, the computed relationships between keff and the core conductivity obtained in the present study are in good agreement with an analytical solution derived from the effective medium theory, a theory which is physically much more relevant for the case at hand than the Zarichnyak-model. The results also show that the observed increase in effective bed conductivity between fully porous and core-shell particle beds frequently observed in literature is not only due to the presence of the core, but that differences in the shell layer conductivity can play an equally important role. In addition, it could also be demonstrated that, if ways could be found to increase the conductivity of the shell layer, this would produce a much stronger increase of the overall bed conductivity than will ever be possible by increasing the conductivity of the cores.
       
  • Simultaneous densitometric determination of eight food colors and four
           sweeteners in candies, jellies, beverages and pharmaceuticals by
           normal-phase high performance thin-layer chromatography using a single
           elution protocol
    • Abstract: Publication date: Available online 31 August 2018Source: Journal of Chromatography AAuthor(s): Anargha P. Nambiar, Mallika Sanyal, Pranav S. ShrivastavAbstractThe present work describes a novel application of high performance thin-layer chromatography for the separation and quantification of eight food colors (amaranth, allura red, erythrosine, fast green, indigo carmine, quinoline yellow, sunset yellow and tartrazine) and four intense sweeteners (acesulfame, aspartame, saccharin and neohesperidin) using a single mobile phase. The analyte zones were detected densitometrically at 210, 295, 450 and 550 nm. The best chromatographic performance for all the additives was achieved using acetonitrile: water: ethyl acetate: 10 % aqueous ammonia (9:1:1:1, v/v/v/v) as the solvent system within 20 min. The developed method was validated as per International Conference on Harmonization (ICH) guidelines for linearity, sensitivity, selectivity, accuracy (recovery), precision (repeatability and reproducibility), robustness and stability. The limit of detection and limit of quantitation ranged from 0.2-9.8 ng/zone and 0.7-29.7 ng/zone respectively and the correlation coefficient ( r2) values for the calibration curves were ≥ 0.9973 for all the additives. The developed method was successfully applied to determine food colors and sweeteners in candies, jellies, beverages and pharmaceuticals with minimal sample processing. The recovery of different additives obtained from food products, beverages and pharmaceuticals ranged from 96.6-106.7 %. The results showed that all the samples contained food additives within the permissible limits. The developed method is simple, precise, accurate and economical for routine quality control of foodstuffs.
       
  • Micro-fabricated packed metal gas preconcentrator for enhanced monitoring
           of ultralow concentration of isoprene
    • Abstract: Publication date: Available online 31 August 2018Source: Journal of Chromatography AAuthor(s): Baoqing Han, Hairong Wang, Hao Huang, Tinghan Liu, Guishan Wu, Jiuhong WangAbstractA novel non-silicon-based micro-preconcentration device, as a pretreatment component in a portable gas chromatography system, was developed for the preconcentration one of the trace volatile organic compounds (VOCs) in the exhaled gases, which is one typical biomarker for the chronic liver disease (CLD). The device was designed as an array of manifold-shaped rectangular metal micro-channels with flat dimensions of 16 mm × 12.6 mm and the internal empty volume is 14.4 μL on the copper substrate. Instead of the non-silicon fabrication process, the traditional laser etching technology (LET) was optimized to etch micro-channels, and vacuum diffusion welding (VDW) was applied to form internal channels. The fabricated chip was filled with Carbopack X adsorbent. In the testing, the metal gas preconcentrator (MGP) was installed in a commercial GC (gas chromatography) and nitrogen was used as carrier gas and desorbed gas. With the MPG, up to 352 of concentration factor can be achieved for 10 ppb isoprene. The developed MGP, which has advantages of high strength, low cost, good thermal conductivities, can potentially be used for non-invasive screening of advanced liver fibrosis by monitoring isoprene concentrations in exhaled breath.
       
  • Liquid chromatography-mass spectrometry based approach for rapid
           comparison of lysophosphatidic acid acyltransferase activity on multiple
           substrates
    • Abstract: Publication date: Available online 29 August 2018Source: Journal of Chromatography AAuthor(s): Tianyu Hou, Matthew C. Taylor, Pushkar Shrestha, Surinder Singh, Zhi-Jun Zhang, Xue-Rong ZhouAbstractLysophosphatidic acid acyltransferases (LPAAT) play an essential role in generating phosphatidic acid (PA), a key intermediate for phospholipids and triacylglycerol synthesis. The individual members have a diversity of localisation, and a strong fatty acid substrate preference. In vitro LPAAT enzymatic activity assays are necessary for understanding the physiological function of these enzymes. In this work, we have developed a liquid chromatography-mass spectrometry (LC-MS) based rapid enzymatic assay without using radioactive labelling. We show that this approach is comparable to radioactive labelling assays, using either native or non-native lysophosphatidic acid receiver molecules. Most importantly, this approach can be applied to the comparison of multiple substrates in a single assay. The approach is also adaptable for other lipid enzymatic assays.
       
  • Electropreconcentration, gate injection, and capillary electrophoresis
           separation on a microchip
    • Abstract: Publication date: Available online 27 August 2018Source: Journal of Chromatography AAuthor(s): Honggu ChunABSTRACTThe nanochannel-based electropreconcentration is not compatible with successive capillary zone electrophoresis (CZE). In this study, the incompatibility is theoretically discussed and experimentally proven, and then, the development of a monolithic glass microfluidic chip for performing integrated electropreconcentration and CZE separation is described. The sample is electropreconcentrated at the interface of a micro- and nanochannel where electric double layer overlap conditions exist. Because an ion-depletion region develops at the leading front of the preconcentrated plug, a field-enhanced sample stacking effect occurs which limits the separation efficiency unless compensated for. The ion-depletion region was confirmed by monitoring the solution conductivity at discrete points in the microchannel during the preconcentration step. The solution conductivity decreased>20-fold during the preconcentration step. To overcome the effects of this region, a cross-intersection was used to shunt the ion-depleted buffer away from the analysis channel while reintroducing the running buffer. When the preconcentrated sample plug arrives at the cross-intersection, it is gate injected into the analysis channel so that fresh running buffer surrounds the plug. Under these conditions, three-peptide mixture was preconcentrated ~200-fold in 60 sec and the preconcentrated plug was successfully resolved with better than 1% relative standard deviations in migration times.
       
  • Investigation of isomeric structures in a commercial mixture of naphthenic
           acids using ultrahigh pressure liquid chromatography coupled to hybrid
           traveling wave ion mobility-time of flight mass spectrometry
    • Abstract: Publication date: Available online 24 August 2018Source: Journal of Chromatography AAuthor(s): Mahmoud M. Yassine, Ewa Dabek-ZlotorzynskaAbstractThe separation of isomeric naphthenic acids (NAs) is of high importance to obtain more detailed and therefore useful information to understand their fate, transport, toxicity and potential removal treatment methodologies. In the current study, the capabilities of the ultrahigh pressure liquid chromatography/traveling wave ion mobility-time of flight mass spectrometry (UPLC/TWIM-TOF-MS) to separate and study different isomeric structures of NAs were investigated. Fifty seven standard compounds belonging to different chemical families of classical NAs were analyzed to obtain their experimental drift times in addition to chromatographic retention time and mass-to-charge information (m/z). These acyclic and cyclic molecules yielded ions with collision cross section (CCS) values ranging from 110 to 210 Å2. The feasibility of the UPLC/TWIM-TOF-MS method to provide a higher degree of confidence in the identification of isomeric structures was evaluated by analyzing the commercial (Sigma-Aldrich) NAs mixture. Identification and structure confirmation of several alicyclic compounds of similar m/z in the NAs mixture were possible by this method. For instance, the presence of previously tentatively identified compounds by the ultrahigh pressure liquid chromatography/quadrupole time of flight mass spectrometry (UPLC/QTOF-MS), such as 4-tert-butylcyclohexanoic acid, 4-dicyclohexylacetic acid or 3,5-dimethyladamantane-1-carboxylic acid, was confirmed. Combining ion mobility separation with UPLC/TOF-MS gives a higher level of selectivity to the overall method by selective interrogation of specific retention time, mass-to-charge and mobility regions. However, there are cases where it is not possible to resolve many similar molecules such as acyclic isomeric compounds in commercial NAs mixture by this technique. This was likely due to the very small CCS area differences among the structural isomeric species. Considerable improvements in the ion mobility resolution and separation will be required for this technique to be able to resolve isomeric species with slight differences in physicochemical properties (e.g., size and structure).
       
  • Moment Analysis for Mass Transfer Kinetics at the Interface of Spherical
           Molecular Aggregates
    • Abstract: Publication date: Available online 24 August 2018Source: Journal of Chromatography AAuthor(s): Kanji MiyabeAbstractNew moment equations were developed on the basis of the principle of relativity for explaining some characteristics of elution peaks measured by electrokinetic chromatography (EKC) using spherical molecular aggregates. Basic equations representing mass balance and mass transfer kinetics in EKC system in a Galilean coordinate system S were transformed to those in another coordinate system S’, which imaginarily moved with respect to S. Moment equations for EKC peaks in S’ in the time domain were derived from the analytical solution of the modified basic equations in the Laplace domain. Moment equations for EKC peaks in S were derived from those in S’ by the inverse Galilean transformation. The moment equations were used to the re-analysis of EKC data previously measured. The values of permeation rate constants of thymol at the interface of sodium dodecylsulfate micelles were fairly in agreement with those determined in a previous study. The moment equations were also used to the numerical simulation of elution peaks in EKC systems. The influence of some experimental parameters on elution peak profiles was quantitatively analyzed. The moment equations are useful for determining the rate constants of interfacial solute permeation from elution peak profiles measured by EKC.
       
  • Universal response quantification approach using a Corona Charged Aerosol
           Detector (CAD) – application on linear and cyclic oligomers extractable
           from polycondensate plastics polyesters, polyamides and polyarylsulfones
    • Abstract: Publication date: Available online 23 August 2018Source: Journal of Chromatography AAuthor(s): Martin Eckardt, Marie Kubicova, Thomas J. SimatAbstractIn terms of risk assessment especially for known and unknown substances migrating from food contact materials, quantification without corresponding reference substances currently poses a challenge. In the present study, the opportunity of a universal response quantification approach was evaluated by using a corona charged aerosol detector (CAD) for liquid chromatography combined with inverse gradient compensation. Characteristics of CAD detection in dependence of substance properties were analyzed with 46 randomly chosen reference substances. An almost equal CAD response (±20%) was achieved for non-volatile substances with a molecular weight of minimum 400 g/mol and a vapor pressure of maximum 10-8 Torr. We empirically defined an analytical parameter, Q50/35, the quotient of CAD peak areas at CAD evaporator temperatures of 50 °C and 35 °C, to predict the adequacy of the CAD universal response approach for quantification of known and unknown analyte substances. Exemplarily, we applied the CAD universal quantification approach for the determination of extractable oligomers below 1000 g/mol from a variety of food contact polycondensate plastic materials (e.g. polyesters like polyethylene terephthalate, polybutylene terephthalate, Tritan copolyester, polyamides 6, 6.6 and 6 T/6I and polyarylsulfones polyphenylsulfone and polyethersulfone). Quantitative results for in total 44 oligomers out of 11 materials were compared with established material-specific quantification methods using extracted oligomer mixtures as well as individual oligomers isolated from the mixtures. CAD-based quantification results were generally in accordance to published quantification approaches for polyamide oligomers and oligomers from polyarylsulfones. For oligomers extracted and isolated from polyester materials a slight underestimation was determined by CAD universal response approach. In terms of detection limits and accuracy, the universal CAD approach exhibits no advantages compared to established UV-methods, too date.
       
  • All on one high-performance thin-layer chromatography plate: solvent-free
           nanomole-scaled on-surface synthesis, workup and online high-resolution
           mass spectrometry for elucidation of two new degradation products in an
           ifosfamide formulation
    • Abstract: Publication date: Available online 23 August 2018Source: Journal of Chromatography AAuthor(s): Imanuel Yüce, Gertrud E. MorlockAbstractOn-surface reactions were introduced as a new strategy for rapid structure elucidation. This strategy is illustrated by the miniaturized synthesis-guided identification of two new degradation products (impurities) occurring in a pharmaceutical formulation of the anti-cancer drug ifosfamide, especially in the presence of urea. Synthesis on the silica gel surface bypassed the need for solvents, as the large nm-porous surface favoured a fast conversion of the reaction partners. For the on-surface synthesis of the impurities, the respective reagents were accurately and automatedly applied in the nanomole scale on a high-performance thin-layer chromatography (HPTLC) silica gel plate. After a fast reaction, the workup of the reaction mixture was performed by development of the HPTLC plate followed by online high-resolution mass spectrometry. As proof of concept and for benchmarking, a reaction mixture obtained from conventional preparative synthesis in a round-bottom flask was analysed in parallel as well as different formulations. The use of adsorbents as inert layer turned out to be highly efficient for a rapid generation and confirmation of impurities, as the synthesis on the HPTLC layer revealed them within 10 minutes. Image evaluation was simply performed by videodensitometry. The advantageous combination of all steps on one HPTLC plate and its resulting efficiency made surface synthesis on chromatographic phases an optimal tool for signal highlighting in mass spectrometry, and thus for the assignment of impurities in drugs. The chemistry process scale was miniaturized down to the µg-level per synthesis (in total 30 60 µg chemicals/reaction), setting a new state-of-the-art standard. All material savings clearly contribute to green chemistry, and this strategy substantially reduces the consumption of chemicals and greatly enhances the analytical efficiency, when adapted by scientists for the quality control of any other chemical product. The combination of synthesis, workup and detection in a miniaturized process, contributes to optimized workflows in a lean laboratory.
       
  • Amino acid and ionic liquid modified polyhedral oligomeric
           silsesquioxane-based hybrid monolithic column for high-efficiency
           capillary liquid chromatography
    • Abstract: Publication date: Available online 23 August 2018Source: Journal of Chromatography AAuthor(s): Manman Han, Wan Li, Rui Chen, Yangyang Han, Xiuhua Liu, Tingting Wang, Huaizhong Guo, Xiaoqiang QiaoAbstractIn this study, a novel amino acid and ionic liquid dual organically functionalized reagents modified polyhedral oligomeric silsesquioxane methacryl substituted (POSS-MA) based hybrid monolithic column (POSS-VBI-Cys) was designed and reported. With amino acid L-cysteine and ionic liquid 1-vinyl-3-butylimidazolium bromide as dual monomers, POSS-MA as the crosslinker, the new POSS-VBI-Cys hybrid monolithic column could be facilely fabricated via the “one-pot” free radical copolymerization and thiol-ene click reaction. Because of the introduction of polar amino acid L-cysteine, the new POSS-VBI-Cys column exhibited attenuated hydrophobicity in reversed-phase liquid chromatography separation. Polar amides, nucleosides and nucleic acid bases displayed strong retention on the POSS-VBI-Cys column and could be successfully separated. Furthermore, the new POSS-VBI-Cys column displayed good separation selectivity for model glycoproteins and non-glycoproteins mixture and it was also successfully used for the purification and separation of TARG1 protein from its originally expressed sample. In the future research, we will further exploit its performances for separation of intact proteins and in-depth proteome applications.
       
  • Determination of polybrominated diphenyl ethers in human serum by gas
           chromatography – inductively coupled plasma mass spectrometry
    • Abstract: Publication date: Available online 23 August 2018Source: Journal of Chromatography AAuthor(s): Matic Bergant, Radmila Milačič, Janez ŠčančarAbstractPolybrominated diphenyl ethers (PBDEs) are flame retardants that are added to a wide range of consumer products. Due to their extensive use in the past, their presence has been documented in multiple environmental compartments and living organisms, including humans. To assess the exposure of humans to PBDEs, a new simple, reliable, and sensitive method was developed for the determination of six PBDE congeners (BDE 28, BDE 47, BDE 99, BDE 100, BDE 153, BDE 154) in human serum by gas chromatography–inductively coupled plasma mass spectrometry (GC-ICP-MS). The PBDEs were extracted from 1 mL ofserum by 30 min of mechanical shaking with formic acid. Subsequently, 2 mL of iso-octane was added and 30 min of mechanical shaking was applied. For clean-up of the extract Florisil column was applied. The analytical method was validated by analysis of human serum standard reference materials SRM 1957 (Non-Fortified Human Serum) and SRM 1958 (Fortified Human Serum). Good agreement of the determined concentrations with those certified was found. The repeatability and reproducibility of the analytical method was within 5.9% and 6.1%, respectively, whereas the limits of detection (LODs) for the PBDEs analysed were between 0.0016 and 0.0039 ng mL−1 wet weight (ww). The feasibility of the method was tested by analysing human serum samples. In this study, the determined concentrations in sera were in a range similar to that of as those reported for certain other European countries.
       
  • Poly(4-vinylpyridine) based novel stationary phase investigated under
           supercritical fluid chromatography conditions
    • Abstract: Publication date: Available online 23 August 2018Source: Journal of Chromatography AAuthor(s): Kanji Nagai, Tohru Shibata, Satoshi Shinkura, Atsushi OhnishiAbstractA novel poly(4-vinylpyridine) based stationary phase was investigated for its performance under supercritical fluid chromatography (SFC) mode. Due to its unique structure, this stationary phase has high molecular planarity recognition ability for aromatic samples possessing the same number of aromatic rings and π-electrons. Taking advantage of the planarity recognition ability observed, separations of structurally similar polycyclic aromatic hydrocarbons and steroids were achieved. This novel stationary phase afforded good peak symmetry for both acidic and basic active pharmaceutical ingredients even when excluding the use of additives such as acids, bases, and salts. These findings may be attributed to the polymeric pyridyl groups covalently-attached on silica gel, which will effectively shield the undesirable interaction between residual silanol groups on the surface and the analytes. Moreover, the properties of pyridyl group on the selector can be reversibly tuned to cationic pyridinium form by eluting trifluoroacetic acid containing modifier. Column robustness toward cycle durability testing was also confirmed.
       
  • Stationary phase based on cellulose dodecanoate physically immobilized on
           silica particles for high-performance liquid chromatography
    • Abstract: Publication date: Available online 23 August 2018Source: Journal of Chromatography AAuthor(s): Andressa T. Vieira, Rosana M.N. Assunção, Anizio M. FariaAbstractThe chemical agent free preparation of a stationary phase using a natural macromolecule was the focus of this paper. Thermal immobilization of cellulose dodecanoate on silica particles was used for the preparation of a stationary phase without the use of chemical reagents. Cellulose modification was performed to produce a hydrophobic macromolecule with solubility in common organic solvents. The new stationary phase was characterized morphologically and physico-chemically, presenting as spherical particles immobilized with a thin cellulose dodecanoate layer. The degree of substitution of cellulose dodecanoate was 1.7, which resulted in a separation mechanism in reversed phase mode, but with lower hydrophobicity and higher steric selectivity, which are properties from cellulose. These characteristics resulted in a stationary phase with intrinsic selectivity that was able to separate mixtures of polar drugs, homologs of an anionic surfactant and omeprazole isomers, which are not well resolved in typical C18 phases. Considering that cellulose is a natural polymer and the preparation method of stationary phase involves only physical processes of silica modification, the final material presents as a stationary phase with specific retention properties coming from both dodecanoate and cellulose.
       
  • Vulnerability of anthocyanins to the components of a thin-layer
           chromatographic system and comprehensive screening of anthocyanes in
           alimentary products
    • Abstract: Publication date: Available online 20 August 2018Source: Journal of Chromatography AAuthor(s): Eliza Łata, Agnieszka Fulczyk, Teresa Kowalska, Mieczysław SajewiczAbstractThe aim of this study was to revisit the TLC authentication of alimentary products concept based on analysis of anthocyanes with the foodstuffs of plant origin. To this effect, we used two anthocyanins (cyanin and keracyanin) and two anthocyanidins (pelargonidin and delphinidin) as phytochemical standards. The first step was to develop a novel method making use of the RP-18 F254s stationary phase (which ensures mixed-mode retention mechanism with the localized adsorption on the non-bonded silanols) and acetic acid as the mobile phase component. Importantly, similar TLC systems are currently used for the analysis of anthocyanes. Individual steps of our method development enabled a deeper insight in vulnerability of anthocyanins to external conditions resulting in hydrolysis thereof. In this study, it was impossible to fully separate the products of hydrolytic degradation of the test anthocyanins in a single development run and it was only triple development which ensured distinct and symmetrically shaped chromatographic spots, further scrutinized with use of mass spectrometry. The identity of the hydrolytically split fractions was additionally studied with use of the p-aminobenzoic acid (PABA) test. To obtain calibration curves, triple development was employed for cyanin, keracyanin, and pelargonidin, while delphinidin was developed in one development run. The respective LOD and LOQ values were: for spot (i) derived from the cyanin standard, 0.005 and 0.016 μg spot-1; for spot (ii) derived from the cyanin standard, 0.006 and 0.017 μg spot-1; for spot (i) derived from the keracyanin standard, 0.092 and 0.274 μg spot-1; for spot (ii) derived from the keracyanin standard, 0.035 and 0.104 μg spot-1; for the pelargonidin standard, 0.013 and 0.040 μg spot-1; and for the delphinidin standard, 0.036 and 0.108 μg spot-1. The developed method was used to identify and quantify cyanin, keracyanin, pelargonidin and delphinidin in selected alimentary products (syrups, juices and herbal infusions), keeping in mind that the obtained numerical results were of semi-quantitative nature only.
       
  • Industrial countercurrent chromatography separations based on a cascade of
           centrifugal mixer-settler extractors
    • Abstract: Publication date: Available online 20 August 2018Source: Journal of Chromatography AAuthor(s): Artak E. Kostanyan, Andrey A. ErastovAbstractIn hydrometallurgy, traditional extraction technologies, in particular, for isolation and purification of rare-earth metals include a number of processing steps using up to hundreds of mixer-settler extractors. These technologies could be greatly simplified by using the methods of countercurrent chromatography (CCC) separation. However, the current CCC equipment cannot process large volumes of feed material formed during the industrial production of these metals. In this paper, the cascade of centrifugal mixer-settler extractors assembled as a multi-stage unit is suggested for industrial application of CCC and discussed.
       
  • Polymeric stationary phases based on poly(butylene terephthalate) and
           poly(4-vinylpirydine) in the analysis of polyphenols using supercritical
           fluid chromatography. Application to bee pollen
    • Abstract: Publication date: Available online 20 August 2018Source: Journal of Chromatography AAuthor(s): Laura Toribio, Sandra Arranz, Ana M. Ares, José BernalAbstractTwo new polymer-based stationary phases; DCpak PBT (poly(butylene terephthalate)) and DCpak P4VP (poly(4-vinylpirydine)) were evaluated for the analysis of polyphenols using supercritical fluid chromatography (SFC). The compounds studied included phenolic acids and flavonoids. The different variables that influence the chromatographic separation, such as type and percentage of organic modifier, additive, pressure and temperature were examined. Using the DCpak P4VP column the retention was exceptionally high, obtaining better results with the DCpak PBT column. The separation of nine polyphenols was achieved using a gradient of modifier (methanol with 0.1% trifluoroacetic acid) from 5 to 50%, a pressure of 150 bar, a temperature of 35 °C and a flow-rate of 2 mL/min. The use of additives was necessary in order to obtain good peak shapes and efficiencies, achieving the best results with trifluoroacetic acid.. LODs and LOQs values were lower than 5 µg/mL in all the cases; meanwhile, the %RSD values for method repeatability and inter-day reproducibility were lower than 3% and 10% respectively. Finally, the proposed method was successfully applied to the analysis of polyphenols in commercial bee pollen; four compounds, namely cinnamic acid, p-coumaric acid, catechin and quercetin were identified and quantified.
       
  • Multi-residue analysis of chiral and achiral trace organic contaminants in
           soil by accelerated solvent extraction and enantioselective liquid
           chromatography tandem-mass spectrometry
    • Abstract: Publication date: Available online 19 August 2018Source: Journal of Chromatography AAuthor(s): Bruce Petrie, Jana Mrazova, Barbara Kasprzyk-Hordern, Kyari YatesReported here is the first analytical methodology for the enantiomeric determination of chiral trace organic contaminants (TOrCs) in soil. Direct enantioselective separations were achieved on a Chirobiotic V2® column operated in polar ionic mode. Initial screening of vancomycin stationary phases found Chirobiotic V2® better suited for multi-residue separation of chiral TOrCs than Chirobiotic V® due to differences in the ligand linkage chemistry. Simultaneous enantioseparation of beta-blockers, beta-agonists, anti-depressants, anti-histamines and stimulants was achieved for the first time. This included the first separation of chlorpheniramine enantiomers with a method suitable for environmental analysis (i.e., coupled to MS). Investigation of mobile phase composition found the concentration of liophilic ions had the greatest influence on enantioseparations and of most importance during method development. The optimized method achieved simultaneous separation of salbutamol, propranolol, atenolol, amphetamine, chlorpheniramine and fluoxetine enantiomers with satisfactory resolution (>1.0). For completeness, such methods also need to support analysis of achiral TOrCs. Therefore three achiral TOrCs (carbamazepine, carbamazepine 10,11 epoxide and triclocarban) were included to demonstrate the methods suitability. Method recoveries for all analytes ranged from 76 to 122 % with method quantitation limits (MQLs)
       
  • Reduction of the extra-column band dispersion by a slow transport of a
           sample band from the injector to the column in isocratic reversed-phase
           liquid chromatography
    • Abstract: Publication date: Available online 19 August 2018Source: Journal of Chromatography AAuthor(s): Ikuma Kuroda, Hideyuki Uzu, Shota Miyazaki, Masayoshi Ohira, Nobuo TanakaAbstractExtra-column band dispersion during the transport of a sample band from the injector to the column can be reduced by a flow rate program starting with a low flow rate until the sample band has approached to, or just entered into the column, followed by an increased flow rate suitable for the solute separation in the column. Such a sample introduction method increased the plate counts of a 50 mm long column, 1.0 or 2.1 mmID, especially for early-eluting solutes by up to several times compared to a conventional elution method, when a 0.254 mmID, 15.2 cm connection tubing was used. Increase in plate counts of up to 50-70% was possible for solutes with retention factors smaller than 1.0 for the columns connected with a 0.13 mmID, 15 cm tube. The method also seems to reduce the contribution of the void space at the column inlet to the band dispersion. The elution method including a slow transport of the sample band in the pre-column space of 10 μL or less may require a little longer separation time than normal elution, but it was shown to be effective for increasing the observed efficiency of a small column for solutes with small retention factors.
       
  • Application of covalent organic framework as the adsorbent for solid-phase
           extraction of trace levels of pesticide residues prior to high-performance
           liquid chromatography-ultraviolet detection
    • Abstract: Publication date: Available online 18 August 2018Source: Journal of Chromatography AAuthor(s): Yuhong Song, Ruiyang Ma, Lin Hao, Xiumin Yang, Chun Wang, Qiuhua Wu, Zhi WangAbstractA covalent organic framework (named as DAAQ-TFP) was prepared via a fast, environmentally-friendly, and easy-to-perform grinding method with 2,6-diaminoanthraquinone (DAAQ) and 1,3,5-triformylphloroglucinol (TFP) as building blocks. The DAAQ-TFP possesses large surface area, high porosity, good thermochemical stability, abundant O atoms and N-H groups, which render it great potential as sorbent for some compounds. It was employed as adsorbent to extract benzoylurea insecticides (BUs) from environmental water, juice, fruit and vegetables samples, followed by their determination with high-performance liquid chromatography (HPLC). The DAAQ-TFP showed a high adsorption capacity for BUs, and the presented method provided a very low limits of detection and high method recoveries. To explore its application potential and also to clarify the possible adsorption mechanisms of the DAAQ-TFP toward BUs, it was tested to extract different types of compounds, proving that the DAAQ-TFP can serve as a superior adsorbent, and adsorption mechanism is mainly based on the π-π stacking and H bonding.
       
  • Rapid analysis of sulfur mustard oxide in plasma using gas
           chromatography-chemical ionization-mass spectrometry for diagnosis of
           sulfur mustard exposure
    • Abstract: Publication date: Available online 18 August 2018Source: Journal of Chromatography AAuthor(s): Erica Manandhar, Adam Pay, Livia A. Veress, Brian A. LogueAbstractSulfur mustard (SM) is the most utilized chemical warfare agent in modern history and has caused more casualties than all other chemical weapons combined. SM still poses a threat to civilians globally because of existing stockpiles and ease of production. Exposure to SM causes irritation to the eyes and blistering of skin and respiratory tract. These clinical signs of exposure to SM can take 6-24 h to appear. Therefore, analyzing biomarkers of SM from biological specimens collected from suspected victims is necessary for diagnosis during this latent period. Here, we report a rapid, simple, and direct quantitative analytical method for an important and early SM biomarker, sulfur mustard oxide (SMO). The method includes addition of a stable isotope labeled internal standard, SMO extraction directly into dichloromethane (DCM), rapid drying and reconstitution of the extract, and direct analysis of SMO using chemical ionization gas chromatography-mass spectrometry (GC-CI-MS). The limit of detection (LOD) of the method was 0.1 μM, with a linear range from 0.5-100 μM. Method selectivity, matrix effect, recovery, and short-term stability were also evaluated. Furthermore, the applicability of the method was tested by analyzing samples from inhalation exposure studies performed in swine. The method was able to detect SMO from 100% of the exposed swine (N = 9), with no interferences present in the plasma of the same swine prior to exposure. The method presented here is the first of its kind to allow for easy and rapid diagnosis of SM poisoning (sample analysis
       
  • Synthesis of cellulose carbamates bearing regioselective substituents at
           2,3- and 6-positions for efficient chromatographic enantioseparation
    • Abstract: Publication date: Available online 18 August 2018Source: Journal of Chromatography AAuthor(s): Jun Shen, Fan Wang, Wanying Bi, Bo Liu, Shuangyan Liu, Yoshio OkamotoAbstractNine cellulose derivatives bearing two different carbamate substituents at 2,3- and 6-positions of a glucose unit were synthesized by a sequential process based on the regioselective protection at 6-position. Their chiral recognition abilities were then evaluated as the chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC) after coating them onto the macroporous silica gel. The introduction of two different phenylcarbamates at 2,3- and 6-positions of glucose unit was comparatively more attractive than that of one phenylcarbamate and one cyclohexylcarbamate to enhance the chiral recognition ability of these cellulose derivatives. Different combination of carbamate substituents of cellulose derivatives seems to offer superior resolution of different racemic compounds. The chiral recognition ability of these derivatives is apparently dependent on the nature, position and number of the substituents on the aromatic moieties. Many derivatives exhibit good enantioselectivity for the racemates in this study, and those based on cellulose 2,3-(3,5-dimethylphenylcarbamate) showed relatively better chiral recognition than others. Some racemates could be even more efficiently resolved on the cellulose derivatives with different carbamate groups at 2,3- and 6-positions than on the cellulose tris(3,5-dimethylphenylcarbamate), which is commercially available as one of the most popular chiral columns, Chiralcel OD. The structures of the obtained cellulose derivatives were also investigated by circular dichroism spectroscopy.
       
  • Speciation of nano and ionic form of silver with capillary
           electrophoresis-inductively coupled plasma mass spectrometry
    • Abstract: Publication date: Available online 17 August 2018Source: Journal of Chromatography AAuthor(s): Bernhard Michalke, Ivana Vinković-VrčekAbstractResearch in the area of new nanomaterials has been given high priority as having an enormous economic potential. Due to marked antimicrobial effect, silver nanoparticles (AgNPs) are one of the most commercialized and successfully exploited nanomaterials in a wide range of medical and consumer products.In biological and environmental compartments, AgNPs undergo different transformations including interaction with organic molecules, such as proteins, and dissolution. Hyphenated systems consisting of capillary electrophoresis (CE) coupled to sensitive element detection like ICP-MS can be considered as the promising methods for speciation analysis of AgNPs. Here, we investigated applicability of different CE methods hyphenated to ICP-MS for speciation of AgNPs in biological systems.The paper presents approach to analyze species formed in interaction of AgNPs with metallothionein (MT) as model protein. As AgNPs might be coated by MTs in bio-fluids, we installed first a CE-speciation method for MT-1 and MT-2. Although this separation was successful, no reproducible and well separated peaks for AgNPs or Ag+ were achieved. Therefore, we focused on developing methods for separating MT-1, MT-2, Ag+ and AgNPs. Several buffer conditions were tested to improve their separation and to minimize Ag-sticking to capillary walls. All compounds of interest in this paper, i.e. MT-1, MT-2, Ag+ and AgNPs, were well separated from each other using tetramethyl-ammoniumhydroxide as electrolyte. In mixed samples, we observed Ag+ being completely associated with MT-1, while Ag+-association with MT-2 was less: The highest quantity of Ag+ was associated with a compound having low Cd-concentration, while another relevant fraction was bound to MT-2. Free Ag+ was also seen in minor amounts whereas another Ag-peak at 8.13 min remains unknown. Most AgNPs remained free. AgNPs were only little associated with MT-1, the latter being split into two peak signals, whereas association with MT-2 was high. Only 15% of AgNPs remained unbound.We demonstrated CE hyphenated to the ICP-MS as promising and elegant technique to study AgNPs in biological systems.
       
  • Preparation and application of guanidyl-functionalized graphene
           oxide-grafted silica for efficient extraction of acidic herbicides by
           Box-Behnken design
    • Abstract: Publication date: Available online 17 August 2018Source: Journal of Chromatography AAuthor(s): Xiudan Hou, Sheng Tang, Xingxiang Guo, Licheng Wang, Xia Liu, Xiaofeng Lu, Yong GuoAbstractA highly selective and efficient extraction material was synthesized through the functionalization of guanidyl onto the graphene oxide-grafted silica via a simple chemical modification, which was designed and proposed to improve the enrichment capacity for acidic herbicides. The extraction material was confirmed by scanning electron microscopy, Fourier transform infrared spectrometry, X-ray photoelectron spectrometry, thermal gravimetric analyzer and zeta potential analysis. Theoretical adsorption energies, static- and dynamic-state binding experiments, and comparative experiments with various adsorbents were investigated to elucidate the adsorption mechanism. The introduction of guanidyl endowed the sorbent with stronger Lewis base property and electron-donating ability, hence, excellent extraction recoveries for acidic herbicides could be obtained. Besides, electrostatic and π-π interactions were considered as two major driving impetuses in the adsorption process. Single-factor experiment and response surface methodology were utilized for the optimization of extraction and desorption conditions. Under the optimized conditions, the wide linearities were obtained with correlation coefficients ranging from 0.9904 to 0.9980, and the method detection limits were in the range of 0.5-2 μg L-1. The relative standard deviation values of the recoveries of five different extractions were 3.0-7.1 %. Coupled with high performance liquid chromatography, the as-proposed method was successfully applied to detect five acidic herbicides in Lycium barbarum (Goji). It turned out that the proposed method provided a promising perspective for the selective extraction and determination of polar acidic compounds in complex samples.
       
 
 
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