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Journal of Chromatography A
Journal Prestige (SJR): 1.378
Citation Impact (citeScore): 4
Number of Followers: 124  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0021-9673
Published by Elsevier Homepage  [3163 journals]
  • Rapid microwave-assisted dispersive micro-solid phase extraction of
           mycotoxins in food using zirconia nanoparticles
    • Authors: Li-Jing Du; Chu Chu; Elisa Warner; Qiu-Yan Wang; Yu-Han Hu; Ke-Jie Chai; Jun Cao; Li-Qing Peng; Yu-Bo Chen; Juan Yang; Qi-Dong Zhang
      Pages: 1 - 12
      Abstract: Publication date: 3 August 2018
      Source:Journal of Chromatography A, Volume 1561
      Author(s): Li-Jing Du, Chu Chu, Elisa Warner, Qiu-Yan Wang, Yu-Han Hu, Ke-Jie Chai, Jun Cao, Li-Qing Peng, Yu-Bo Chen, Juan Yang, Qi-Dong Zhang
      Mycotoxins are a group of secondary fungi metabolites present in foods that cause adverse effects in humans and animals. The objective of this study was to develop and validate a reliable and sensitive method to determine the presence of fumonisin B1, aflatoxin B1, ochratoxin B, T-2 toxin, ochratoxin A and zearalenone. A rapid, effective process, which involves microwave-assisted dispersive micro-solid phase extraction (MA-d-μ-SPE), has been proposed for the extraction and detection of 6 mycotoxins in peach seed, milk powder, corn flour and beer sample matrixes, for subsequent analysis by ultra-high-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (UHPLC-Q-TOF/MS). Several experimental parameters (type of dispersant, concentration of dispersant, vortex time, type of desorption solvent and pH) affecting the extraction efficiency were systematically studied and optimized. The optimum extraction conditions involved immersing 2.5 μg/mL of nano zirconia (as dispersant) in a 5 mL sample solution. After 2 min of extraction by vigorous shaking, the target analytes were desorbed by 100 μL of chloroform at pH 4.5. The results indicated good linearity in the range of 0.0074-3.6 μg/mL (r ≥ 0.9982), low limits of detection (0.0036-0.033 μg/kg for solid samples and 0.0022–0.017 ng/mL for beer), acceptable reproducibility (relative standard deviation (RSD%) 2.08–2.76% for retention time and 3.51–4.59% for peak area, n = 3), and satisfactory spiked recoveries (84.27–104.96%) for studied mycotoxins in sample matrixes, which demonstrated that MA-d-μ-SPE coupled with UHPLC-Q-TOF/MS is a useful tool for analysis of multi-mycotoxin.

      PubDate: 2018-06-08T09:27:27Z
      DOI: 10.1016/j.chroma.2018.05.031
      Issue No: Vol. 1561 (2018)
       
  • Hybrid-type carbon microcoil-chitosan composite for selective extraction
           of aristolochic acid I from Aristolochiaceae medicinal plants
    • Authors: Hua Shu; YanHui Ge; Xin-Ya Xu; Peng-Qi Guo; Zhi-Min Luo; Wei Du; Chun Chang; Rui-Lin Liu; Qiang Fu
      Pages: 13 - 19
      Abstract: Publication date: 3 August 2018
      Source:Journal of Chromatography A, Volume 1561
      Author(s): Hua Shu, YanHui Ge, Xin-Ya Xu, Peng-Qi Guo, Zhi-Min Luo, Wei Du, Chun Chang, Rui-Lin Liu, Qiang Fu
      Aristolochic acid I is a nephrotoxic compound widely existing in many kinds of traditional Chinese medicines, especially in Aristolochiaceae medicinal plants. In this study, chitosan modified carbon microcoils were designed and prepared for the selective separation of aristolochic acid I from medicinal herbs. Successful modification of carbon microcoils was confirmed by scanning electron microscopy, Fourier-transfer infrared spectroscopy, elemental analysis, X-ray photoelectron spectroscopy, and thermogravimetric analyses. The effects of adsorption conditions were investigated and it was determined that the adsorption of aristolochic acid I was controlled by pH. Adsorption isotherms, kinetics, and selectivity tests were performed to evaluate the adsorption capacity and selectivity of the modified carbon microcoils. The chitosan modified carbon microcoils exhibited excellent binding ability (77.72 mg g−1) and satisfactory selectivity. Finally, this material was used in solid phase extraction combined with HPLC to enrich and detect aristolochic acid I from medicinal plants. The detector response for aristolochic acid I was linear from 0.5 to 150 mg L−1, and the recoveries of aristolochic acid I ranged from 73.61 to 77.73% with the relative standard deviations of less than 5%. Thus, chitosan modified carbon microcoils were ideal adsorbents for the selective extraction of aristolochic acid I from Aristolochiaceae plants.
      Graphical abstract image

      PubDate: 2018-06-08T09:27:27Z
      DOI: 10.1016/j.chroma.2018.05.037
      Issue No: Vol. 1561 (2018)
       
  • Determination of organochlorine compounds in fish liver by
           ultrasound-assisted dispersive liquid–liquid microextraction based on
           solidification of organic droplet coupled with gas chromatography-electron
           capture detection
    • Authors: Ankita Asati; G.N.V Satyanarayana; V. Tanmya Srivastava; Devendra K. Patel
      Pages: 20 - 27
      Abstract: Publication date: 3 August 2018
      Source:Journal of Chromatography A, Volume 1561
      Author(s): Ankita Asati, G.N.V Satyanarayana, V. Tanmya Srivastava, Devendra K. Patel
      A simple and rapid method for the extraction of organochlorine compounds (OCs) including poly-chlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in fish liver using ultrasound assisted dispersive liquid–liquid microextraction based on the solidification of floating organic droplet (US-DLLME-SFO) was developed. For reducing the complexity of the matrix, the sample was pre-treated prior to microextraction. Factors affecting US-DLLME-SFO were optimized by using statistical design of experiment (DoE). The analysis was carried out by Gas Chromatography (GC) equipped with micro electron capture detector (μ-ECD). The optimized parameters were 4.8 min of ultrasound, 3.0 mL of Milli-Q and 24 μL of 1-undecanol as an extraction solvent as determined by DoE. US-DLLME-SFO was validated in terms of limit of detection, limit of quantification, dynamic linearity range, coefficient of determination (linearity) and extraction recovery in fish liver for OCs, and the respective values were (1.06-3.84 ng g−1), (3.50-12.67 ng g−1), (1.0–500 ng g−1), (R2 = 0.994-0.999), (88.5-108.4%). Interday and intraday precisions were evaluated as relative standard deviation (% RSD) and the values were ≤10%.

      PubDate: 2018-06-08T09:27:27Z
      DOI: 10.1016/j.chroma.2018.05.035
      Issue No: Vol. 1561 (2018)
       
  • Magnetic molecularly imprinted polymer nanoparticles for simultaneous
           extraction and determination of 6-mercaptopurine and its active metabolite
           thioguanine in human plasma
    • Authors: Olivia A. Attallah; Medhat A. Al-Ghobashy; Ahmed Taha Ayoub; Marianne Nebsen
      Pages: 28 - 38
      Abstract: Publication date: 3 August 2018
      Source:Journal of Chromatography A, Volume 1561
      Author(s): Olivia A. Attallah, Medhat A. Al-Ghobashy, Ahmed Taha Ayoub, Marianne Nebsen
      Cytotoxic drugs used in cancer chemotherapy require the continuous monitoring of their plasma concentration levels for dose adjustment purposes. Such condition necessitates the presence of a sensitive technique for accurate extraction and determination of these drugs together with their active metabolites. In this study a novel solid phase extraction technique using magnetic molecularly imprinted nanoparticles (MMI-SPE) is combined with liquid chromatography tandem mass spectrometry (LC–MS/MS) to extract and determine the anti-leukemic agent; 6-mercaptopurine (6-MP) and its active metabolite thioguanine (TG) in human plasma. The magnetic molecularly imprinted nanoparticles (Fe3O4@MIP NPs) were synthesized via precipitation polymerization technique and were characterized using different characterization methods A computational approach was adopted to help in the choice of the monomer used in the fabrication process. The Fe3O4@MIPs NPs possessed a highly improved imprinting efficiency, fast adsorption kinetics following 2nd order kinetics and good adsorption capacity of 1.0 mg/g. The presented MMI-SPE provided the optimum approach in comparison to other reported ones to achieve good extraction recovery and matrix effect of trace levels of 6-MP and TG from plasma. Chromatographic separation was carried out using a validated LC–MS/MS assay and recovery, matrix effect and process efficiency were evaluated. Recovery of 6-MP and TG was in the range of 85.94–103.03%, while, matrix effect showed a mean percentage recovery of 85.94–97.62% and process efficiency of 85.54–96.18%. The proposed extraction technique is simple, effective and can be applicable to the extraction and analysis of other pharmaceutical compounds in complex matrices for therapeutic drug monitoring applications.

      PubDate: 2018-06-08T09:27:27Z
      DOI: 10.1016/j.chroma.2018.05.038
      Issue No: Vol. 1561 (2018)
       
  • Application of non-ionic surfactant as a developed method for the
           enhancement of two-phase solvent bar microextraction for the simultaneous
           determination of three phthalate esters from water samples
    • Authors: Samereh Ranjbar Bandforuzi; Mohammad Reza Hadjmohammadi
      Pages: 39 - 47
      Abstract: Publication date: 3 August 2018
      Source:Journal of Chromatography A, Volume 1561
      Author(s): Samereh Ranjbar Bandforuzi, Mohammad Reza Hadjmohammadi
      The extraction of phthalate esters (PEs) from aqueous matrices using two-phase solvent bar microextraction by organic micellar phase was investigated. A short hollow fiber immobilized with reverse micelles of Brij 35 surfactant in 1-octanol was served as the solvent bar for microextraction. Experimental results show that the extraction efficiency were much higher using two-phase solvent bar microextraction based on non-ionic surfactant than conventional two-phase solvent bar microextraction because of a positive effect of surfactant-containing extraction phase in promoting the partition process by non-ionic intermolecular forces such as polar and hydrophobicity interactions. The nature of the extraction solvent, type and concentration of non-ionic surfactant, extraction time, sample pH, temperature, stirring rate and ionic strength were the effecting parameters which optimized to obtain the highest extraction recovery. Analysis of recovered analytes was carried out with high performance liquid chromatography coupled with ultraviolet detection (HPLC–UV). Under the optimum conditions, linearity was observed in the range of 1–800 ng mL−1 for dimethylphthalate (DMP) and 0.5–800 ng mL−1 for diethylphthalate (DEP) and di-n-butyl phthalate (DBP) with correlation determination values above 0.99 for them. The limits of detection and quantification were ranged from 0.012 to 0.03 ng mL−1 and 0.04–0.1 ng mL−1, respectively. The ranges of intra-day and inter-day RSD (n = 3) at 20 ng mL−1 of PEs were 1.8–2.1% and 2.1–2.6%, respectively. Results showed that developed method can be a very powerful, innovative and promising sample preparation technique in PEs analysis from environmental and drinking water samples.

      PubDate: 2018-06-08T09:27:27Z
      DOI: 10.1016/j.chroma.2018.05.039
      Issue No: Vol. 1561 (2018)
       
  • High-throughput and selective solid-phase extraction of urinary
           catecholamines by crown ether-modified resin composite fiber
    • Authors: LiQin Chen; Hui Wang; Zhen Xu; QiuYue Zhang; Jia Liu; Jun Shen; WanQi Zhang
      Pages: 48 - 55
      Abstract: Publication date: 3 August 2018
      Source:Journal of Chromatography A, Volume 1561
      Author(s): LiQin Chen, Hui Wang, Zhen Xu, QiuYue Zhang, Jia Liu, Jun Shen, WanQi Zhang
      In the present study, we developed a simple and high-throughput solid phase extraction (SPE) procedure for selective extraction of catecholamines (CAs) in urine samples. The SPE adsorbents were electrospun composite fibers functionalized with 4-carboxybenzo-18-crown-6 ether modified XAD resin and polystyrene, which were packed into 96-well columns and used for high-throughput selective extraction of CAs in healthy human urine samples. Moreover, the extraction efficiency of packed-fiber SPE (PFSPE) was examined by high performance liquid chromatography coupled with fluorescence detector. The parameters affecting the extraction efficiency and impurity removal efficiency were optimized, and good linearity ranging from 0.5 to 400 ng/mL was obtained with a low limit of detection (LOD, 0.2–0.5 ng/mL) and a good repeatability (2.7%–3.7%, n = 6). The extraction recoveries of three CAs ranged from 70.5% to 119.5%. Furthermore, stable and reliable results obtained by the fluorescence detector were superior to those obtained by the electrochemical detector. Collectively, PFSPE coupled with 96-well columns was a simple, rapid, selective, high-throughput and cost-efficient method, and the proposed method could be applied in clinical chemistry.

      PubDate: 2018-06-08T09:27:27Z
      DOI: 10.1016/j.chroma.2018.05.041
      Issue No: Vol. 1561 (2018)
       
  • Integrated approach for confidence-enhanced quantitative analysis of
           herbal medicines, Cistanche salsa as a case
    • Authors: Wenjing Liu; Qingqing Song; Yu Yan; Yao Liu; Peng Li; Yitao Wang; Pengfei Tu; Yuelin Song; Jun Li
      Pages: 56 - 66
      Abstract: Publication date: 3 August 2018
      Source:Journal of Chromatography A, Volume 1561
      Author(s): Wenjing Liu, Qingqing Song, Yu Yan, Yao Liu, Peng Li, Yitao Wang, Pengfei Tu, Yuelin Song, Jun Li
      Although far away from perfect, it is practical to assess the quality of a given herbal medicine (HM) through simultaneous determination of a panel of components. However, the confidences of the quantitative outcomes from LC–MS/MS platform risk several technical barriers, such as chemical degradation, polarity range, concentration span, and identity misrecognition. Herein, we made an attempt to circumvent these obstacles by integrating several fit-for-purpose techniques, including online extraction (OLE), serially coupled reversed phase LC-hydrophilic interaction liquid chromatography (RPLC-HILIC), tailored multiple reaction monitoring (MRM), and relative response vs. collision energy curve (RRCEC) matching. Confidence-enhanced quantitative analysis of Cistanche salsa (Csa), a well-known psammophytic species and tonic herbal medicine, was conducted as a proof-of-concept. OLE module was deployed to prohibit chemical degradation, in particular E/Z-configuration transformation for phenylethanoid glycosides. Satisfactory retention took place for each analyte regardless of polarity because of successive passing through RPLC and HILIC columns. Optimum parameters for the minor components, at the meanwhile of inferior ones for the abundant ingredients, ensured the locations of all contents in the linear ranges. The unequivocal assignment of the captured signals was achieved by matching retention times, ion transitions, and more importantly, RRCECs between authentic compounds and suspect peaks. Diverse validation assays demonstrated the newly developed method to be reliable. Particularly, the distribution of mannitol rather than galactitol was disclosed although these isomers showed identical retention time and ion transitions. The contents of 21 compounds-of-interest were definitively determined in Csa as well as two analogous species, and the quantitative patterns exerted great variations among not only different species but different Csa samples. Together, the fortification of OLE–RPLC-HILIC–tailored MRM with RRCEC matching could fully address the demands from confidence-enhanced quantitative analysis of HMs.

      PubDate: 2018-06-08T09:27:27Z
      DOI: 10.1016/j.chroma.2018.05.045
      Issue No: Vol. 1561 (2018)
       
  • Theoretical and experimental investigation of the focusing position in
           asymmetrical flow field-flow fractionation (AF4)
    • Authors: Jia-Lan Wang; Enrica Alasonati; Paola Fisicaro; Marc F. Benedetti; Michel Martin
      Pages: 67 - 75
      Abstract: Publication date: 3 August 2018
      Source:Journal of Chromatography A, Volume 1561
      Author(s): Jia-Lan Wang, Enrica Alasonati, Paola Fisicaro, Marc F. Benedetti, Michel Martin
      To better understand the focusing process and to determine the focusing position (zfoc ) in Asymmetrical Flow Field-Flow Fractionation (AF4), theoretical and experimental studies were performed. A new theoretical expression that allows the calculation of zfoc in AF4 channels of any shape having an axial plane of symmetry was established. The equation was then applied to the particular case of a trapezoidal AF4 channel with tapered ends. The applicability of this equation was verified by comparing the calculated results with the experimental measures of the focusing position obtained using blue dextran dye under different flow conditions. The calculated values and the experimental results were in good agreement. The total uncertainty associated with the calculated zfoc was evaluated and was lower than 10%. A good repeatability and reproducibility of the focusing position was obtained. Moreover, the effects of the sample-injection position, the spacer thickness, the membrane aging, and the nature of the injected sample on the focusing position were investigated: zfoc was not influenced by these parameters, proving the universal applicability of the equation given in this work for predicting the focusing position, when the assumption of constancy of the cross-flow velocity at the membrane, which underlies this equation, is fulfilled. Additionally, it is notable that this theoretical expression is suitable for different models of AF4 channel and not peculiar to specific suppliers.

      PubDate: 2018-06-08T09:27:27Z
      DOI: 10.1016/j.chroma.2018.04.056
      Issue No: Vol. 1561 (2018)
       
  • Hyphenation of capillary electrophoresis to inductively coupled plasma
           mass spectrometry with a modified coaxial sheath-flow interface
    • Authors: Hannah U. Holtkamp; Stuart J. Morrow; Mario Kubanik; Christian G. Hartinger
      Pages: 76 - 82
      Abstract: Publication date: 3 August 2018
      Source:Journal of Chromatography A, Volume 1561
      Author(s): Hannah U. Holtkamp, Stuart J. Morrow, Mario Kubanik, Christian G. Hartinger
      Capillary electrophoretic analyses benefit significantly from hyphenation to mass spectrometric techniques. While the coupling to ESI–MS is routinely performed, for example by using a coaxial sheath-flow interface, hyphenating it to inductively coupled plasma mass spectrometry is more technically challenging. We use a commercially available coaxial sheath-flow interface (CSFI) and a simple PTFE-based end-cap for easy, inexpensive CE–ICP-MS hyphenation with improved sensitivity and analytical performance compared to commercially available interfaces. We have optimized key nebulizer parameters such as capillary position, sheath liquid flow rate, and carrier gas flow rate, and compared the CSFI with a commercially available interface. In a set of proof-of-principle experiments employing the anticancer agent cisplatin it was demonstrated that the signal to noise response and sensitivity were considerably improved leading to detection limits for 195Pt of 0.08 μM.

      PubDate: 2018-06-08T09:27:27Z
      DOI: 10.1016/j.chroma.2018.05.036
      Issue No: Vol. 1561 (2018)
       
  • Design keys for paper-based concentration gradient generators
    • Authors: Federico Schaumburg; Raúl Urteaga; Pablo A. Kler; Claudio L.A. Berli
      Pages: 83 - 91
      Abstract: Publication date: 3 August 2018
      Source:Journal of Chromatography A, Volume 1561
      Author(s): Federico Schaumburg, Raúl Urteaga, Pablo A. Kler, Claudio L.A. Berli
      The generation of concentration gradients is an essential operation for several analytical processes implemented on microfluidic paper-based analytical devices. The dynamic gradient formation is based on the transverse dispersion of chemical species across co-flowing streams. In paper channels, this transverse flux of molecules is dominated by mechanical dispersion, which is substantially different than molecular diffusion, which is the mechanism acting in conventional microchannels. Therefore, the design of gradient generators on paper requires strategies different from those used in traditional microfluidics. This work considers the foundations of transverse dispersion in porous substrates to investigate the optimal design of microfluidic paper-based concentration gradient generators (μPGGs) by computer simulations. A set of novel and versatile μPGGs were designed in the format of numerical prototypes, and virtual experiments were run to explore the ranges of operation and the overall performance of such devices. Then physical prototypes were fabricated and experimentally tested in our lab. Finally, some basic rules for the design of optimized μPGGs are proposed. Apart from improving the efficiency of mixers, diluters and μPGGs, the results of this investigation are relevant to attain highly controlled concentration fields on paper-based devices.

      PubDate: 2018-06-08T09:27:27Z
      DOI: 10.1016/j.chroma.2018.05.040
      Issue No: Vol. 1561 (2018)
       
  • Solid-phase extraction, quantification, and selective determination of
           microcystins in water with a gold-polypyrrole nanocomposite sorbent
           material
    • Authors: Amila M. Devasurendra; Dilrukshika S.W. Palagama; Ahmad Rohanifar; Dragan Isailovic; Jon R. Kirchhoff; Jared L. Anderson
      Pages: 1 - 9
      Abstract: Publication date: 27 July 2018
      Source:Journal of Chromatography A, Volume 1560
      Author(s): Amila M. Devasurendra, Dilrukshika S.W. Palagama, Ahmad Rohanifar, Dragan Isailovic, Jon R. Kirchhoff, Jared L. Anderson
      A novel sorbent material, gold-polypyrrole (Au-PPy) nanocomposite-coated silica, is described for the efficient solid-phase extraction (SPE) of six common microcystins (MCs) well below the recommended United States EPA and World Health Organization (WHO) guidelines. With the optimized SPE protocol, samples spiked with MCs were determined at ng/L concentrations by liquid chromatography-mass spectrometry (LC–MS) in different aqueous sample matrices, including HPLC-grade, tap, and lake water. The average recoveries for all MCs tested in the three water matrices ranged from 94.1–103.2% with relative standard deviations (RSDs) of 1.6–5.4%, which indicated excellent extraction efficiency and reproducibility. Limits of detection (LODs) and limits of quantification (LOQs) for all MCs in both tap and lake water samples were determined to be ≤1.5 ng/L and 5.0 ng/L, respectively. The Au-PPy nanocomposite-coated sorbent material was reusable for at least three independent MC extractions with a single SPE cartridge in the concentration range of 10–500 ng/L. Importantly, off-column selective separation at the sample preparation and preconcentration stage between more hydrophilic and more hydrophobic MCs was achieved by sequential elution through changes in the solvent composition and SPE bed size. Therefore, the Au-PPy nanocomposite-coated silica sorbent is a promising new material for the quantification of MC variants in water samples.

      PubDate: 2018-06-02T07:43:06Z
      DOI: 10.1016/j.chroma.2018.04.027
      Issue No: Vol. 1560 (2018)
       
  • Magnetic halloysite nanotube/polyaniline/copper composite coupled with gas
           chromatography–mass spectrometry: A rapid approach for determination of
           nitro-phenanthrenes in water and soil samples
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Mohammad Darvishnejad, Homeira Ebrahimzadeh
      A fast, sensitive and reliable ultrasound-assisted magnetic dispersive solid-phase microextraction (UAMDSPME) setup was developed and evaluated for the enrichment of nitro- phenanthrenes compound in environmental samples prior to GC–MS determination. A new type of nanocomposite sorbent was made based on halloysite nanotubes (HNTs). HNTs is a type of natural material, have attracted great interest because of their large surface area and high chemical and thermal stability. The hybrid nanocomposite (magnetic HNT@PANI@Cu) was obtained by coating the magnetic HNTs by polyaniline (PANI) and afterwards decorating with metalic copper. Its morphology and surface properties were characterized using Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, energy dispersive spectroscopy and vibrating sample magnetometry. In this work several factors that may affect the extraction efficiencies such as desorption solvent type and its volume, sonication times for extraction and desorption, sorbent amount, organic modifier content, salt concentration and matrix effect were investigated in detail. Under the optimal conditions, the limit of detection (S/N = 3) was 0.25 ng L−1 and the linearity was in the range of 0.01–100 μg L−1. The method precision expressed as relative standard deviations (RSDs%) were 4.6-6.1% (intra-day), and 7.2-9.6% (inter-day). Finally, the presented method was successfully applied to the rapid determination of trace levels of nitro-phenanthrenes in spiked water and soil samples.

      PubDate: 2018-06-20T06:47:12Z
       
  • Design, characterization and comparison of materials based on β and γ
           cyclodextrin covalently connected to microporous silica for environmental
           analysis
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Carolina Belenguer-Sapiña, Enric Pellicer-Castell, Jamal El Haskouri, Carmen Guillem, Ernesto Francisco Simó-Alfonso, Pedro Amorós, Adela Mauri-Aucejo
      Determination of organic pollutants in environmental samples presents great difficulties due to the lack of sensitivity and selectivity in many of the existing analytical methods. In this work, the efficiency of materials based on silica structures containing bounded γ-cyclodextrin has been evaluated to determinate phenolic compounds and polycyclic aromatic hydrocarbons in air and water samples, respectively, in comparison with materials made of β-cyclodextrin. According to the results obtained for the material characterization, the new γ-cyclodextrin solid phase does not apparently present any porosity when used in air samples, but it has been shown to work efficiently for the preconcentration of polycyclic aromatic hydrocarbons in water, with recoveries around 80%. In addition, the use of the β-cyclodextrin material for phenolic compounds sampling can be highlighted with recoveries between 83% and 95%, and recoveries for 4-vinylphenol and 2-methoxy-4-vinylphenol have been especially improved in comparison with the use of materials containing trapped β-cyclodextrin in our previous researches. The observed phenomena can be explained on the basis of the analyte molecules size and the diameter of the cyclodextrin cavities, the influence of the cyclodextrin type in the material structure as well as on the interactions taking place with the pollutants and the influence of the matrix type in the retention and desorption mechanisms.

      PubDate: 2018-06-20T06:47:12Z
       
  • Combination of electromembrane extraction and electro-assisted
           liquid-liquid microextraction: A tandem sample preparation method
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Saeed Nojavan, Hossein Shaghaghi, Turaj Rahmani, Ali Shokri, Mahnaz Nasiri-Aghdam
      As a well-known extraction procedure, electromembrane extraction (EME) was combined with electro-assisted liquid-liquid microextraction (EA-LLME) in the present work, which resulted in a promising method. This hyphenated sample preparation method, named EME-EA-LLME, was followed by GC for the determination of two model analytes (clomipramine and imipramine). The effective parameters of both EME and EA-LLME (such as organic solvent, pH of acceptor and sample solutions, voltage and extraction time) were optimized. The proposed EME-EA-LLME procedure demonstrated good linearity with coefficients of determination, R2 ≥ 0.998 over the concentration range of 0.5–750 ng/mL. Limit of detection for both analytes was 0.15 ng/mL. The corresponding repeatability ranged from 6.9 to 12.2% (n = 3). The high enrichment factors were obtained as 770.3 and 561.4 for imipramine and clomipramine, respectively. The advantages of this tandem sample preparation method were low detection limits, simplicity, low cost, and short analysis time (<10 min). Finally, the optimized method was used to extract and determine the analytes in urine and wastewater samples. Overall, the results revealed that the developed EME-EA-LLME procedure had better extraction efficiency in comparison with EME and EA-LLME alone.

      PubDate: 2018-06-20T06:47:12Z
       
  • Conversion of calibration curves for accurate estimation of molecular
           weight averages and distributions of polyether polyols by conventional
           size exclusion chromatography
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Xiuqing Xu, Xiuhan Yang, Steven J. Martin, Edwin Mes, Junlan Chen, David M. Meunier
      Accurate measurement of molecular weight averages ( M ¯ n, M ¯ w, M ¯ z) and molecular weight distributions (MWD) of polyether polyols by conventional SEC (size exclusion chromatography) is not as straightforward as it would appear. Conventional calibration with polystyrene (PS) standards can only provide PS apparent molecular weights which do not provide accurate estimates of polyol molecular weights. Using polyethylene oxide/polyethylene glycol (PEO/PEG) for molecular weight calibration could improve the accuracy, but the retention behavior of PEO/PEG is not stable in THF-based (tetrahydrofuran) SEC systems. In this work, two approaches for calibration curve conversion with narrow PS and polyol molecular weight standards were developed. Equations to convert PS-apparent molecular weight to polyol-apparent molecular weight were developed using both a rigorous mathematical analysis and graphical plot regression method. The conversion equations obtained by the two approaches were in good agreement. Factors influencing the conversion equation were investigated. It was concluded that the separation conditions such as column batch and operating temperature did not have significant impact on the conversion coefficients and a universal conversion equation could be obtained. With this conversion equation, more accurate estimates of molecular weight averages and MWDs for polyether polyols can be achieved from conventional PS-THF SEC calibration. Moreover, no additional experimentation is required to convert historical PS equivalent data to reasonably accurate molecular weight results.

      PubDate: 2018-06-20T06:47:12Z
       
  • Aptamer-based polyhedral oligomeric silsesquioxane (POSS)-containing
           hybrid affinity monolith prepared via a “one-pot” process for
           selective extraction of ochratoxin A
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Yiqiong Chen, Maolin Chen, Jinxin Chi, Xia Yu, Yongxuan Chen, Xucong Lin, Zenghong Xie
      A novel aptamer-based polyhedral oligomeric silsesquioxane (POSS)-containing hybrid affinity monolith has been prepared with a facile “one-pot” process simultaneously via “free radical polymerization” and “thiol-ene” click reaction, and used for on-line selective extraction and practical analysis to trace ochratoxin A (OTA). By using the ternary porogenic mixture composed of water/DMF/PEG, a homogeneous polymerization mixture with POSS chemicals, acrylate-based monomers and aptamer aqueous solution was obtained, and the copolymerization of POSS chemicals, polymer monomers and aptamer aqueous solution was systematically studied. Characterizations such as the morphology, FT-IR and fluorescence spectra, mechanical stability, dynamic binding capacity, cross-reactivity and selectivity of the resultant affinity monolith were also evaluated. Attributed to the porous monolithic structure and aptamer-based affinity interaction, acceptable selective recognition and recovery yields towards trace OTA were obtained. With a 5-fold volume enrichment, the limit of detection (LOD) and limit of quantitation (LOQ) of OTA in fortified beer samples were gained at 0.025 ng/mL (S/N = 3) and 0.045 ng/mL (S/N = 10), respectively. It could be competent for the sensitive measure of actual OTA residues in real beer samples. In comparison with the previously reported strategies containing common “sol-gel” chemistry, the proposed protocol to fabricating aptamer-modified POSS-containing hybrid affinity monolith showed a simpler preparation with acceptable selectivity and higher recovery to trace OTA.

      PubDate: 2018-06-20T06:47:12Z
       
  • Key parameters controlling the development of constant-pattern isotachic
           trains of two rare earth elements in ligand-assisted displacement
           chromatography
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Hoon Choi, David Harvey, Yi Ding, Nien-Hwa Linda Wang
      Ligand-assisted displacement chromatography (LAD) has been developed for separating rare earth elements since the 1950’s. Isotachic displacement trains, which are similar to those in conventional displacement chromatography, were reported previously. However, there has been no general theory delineating the conditions required to form constant-pattern displacement trains for non-ideal systems (or systems with significant mass transfer resistance). The constant-pattern state is critical for obtaining pure products with high yield and high productivity. Without theoretical guidance, all the previous studies found the constant–pattern state by experimental trial and error, which was time consuming and costly. In this study, an efficient rate model and simulations of LAD were developed and verified with experimental data for non-ideal systems. Verified simulations were used to understand the mechanisms of separations and the transition from the transient state to the constant-pattern state. The key dimensionless factors affecting the transition for binary non-ideal systems were identified. Dimensionless groups were developed to reduce the number of variables. Simulations were used to find the transition points fromthe transient state to the constant-pattern state, which indicates the minimum dimensionless column lengths in the multi-parameter space. Strategic combination of the key dimensionless groups allows the minimum dimensionless column lengths to correlate with the combined groups in a two-dimensional diagram (or a map). The correlation curve divides the multi-dimensional space into the transient region and the constant-pattern region. The correlation was further verified with five sets of experiments. It can be used to find, without process simulations or experiments, the minimum column lengths for developing constant-pattern isotachic trains for non-ideal systems, which is useful for designing efficient ligand-assisted displacement chromatography at any scale.

      PubDate: 2018-06-20T06:47:12Z
       
  • Separation of tartronic and glyceric acids by simulated moving bed
           chromatography
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Lucas C.D. Coelho, Nelson M.L. Filho, Rui P.V. Faria, Alexandre F.P. Ferreira, Ana M. Ribeiro, Alírio E. Rodrigues
      The SMB unit developed by the Laboratory of Separation and Reaction Engineering (FlexSMB-LSRE®) was used to perform tartronic acid (TTA) and glyceric acid (GCA) separation and to validate the mathematical model in order to determine the optimum operating parameters of an industrial unit. The purity of the raffinate and extract streams in the experiments performed were 80% and 100%, respectively. The TTA and GCA productivities were 79 and 115 kg per liter of adsorbent per day, respectively and only 0.50 cubic meters of desorbent were required per kilogram of products. Under the optimum operating conditions, which were determined through an extensive simulation study based on the mathematical model developed to predict the performance of a real SMB unit, it was possible to achieve a productivity of 86 kg of TTA and 176 kg of GCA per cubic meter of adsorbent per day (considering the typical commercial purity value of 97% for both compounds) with an eluent consumption of 0.30 cubic meters per kilogram of products.

      PubDate: 2018-06-20T06:47:12Z
       
  • Halogen bond in high-performance liquid chromatography enantioseparations:
           Description, features and modelling
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Roberto Dallocchio, Alessandro Dessì, Maurizio Solinas, Antonio Arras, Sergio Cossu, Emmanuel Aubert, Victor Mamane, Paola Peluso
      Halogen bond (XB)-driven enantioseparations involve halogen-centred regions of electronic charge depletion (σ-hole) as electrophilic recognition sites. The knowledge in this field is still in its infancy. Indeed, although the influence of halogens on enantioseparation have been often considered, only recently the function of electrophilic halogens (Cl, Br, I) as enantioseparations ‘drivers’ has been demonstrated by our groups. Further to these studies, in this paper we focus on some unexplored issues. First, as XB-driven chiral recognition mechanisms are at an early stage of comprehension, a theoretical investigation based on a series of 32 molecular dynamic (MD) simulations was performed by using polyhalogenated 4,4′-bipyridines and polysaccharide-based polymers as ligands and receptors, respectively. Enantiomer elution orders (EEOs) were derived from calculations and the theoretical model accounted for some analyte- and chiral stationary phase (CSP)-dependent experimental EEO inversions. Then, the function of halogen-centred σ-holes in competitive systems, presenting also hydrogen bond (HB) centres as recognition sites, was considered. In this regard, Pirkle’s enantioseparations of halogenated compounds performed on Whelk-O1 were theoretically re-examined and electrostatic potentials (EPs) associated with both σ-holes on halogens and HB centres were computed and compared. Then, the enantioseparation of halogenated 2-nitro-1-arylethanols was performed on cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) and the influence of halogen substituents on the chromatographic results was evaluated by correlating theoretical and experimental data.

      PubDate: 2018-06-20T06:47:12Z
       
  • A new method to prepare and redefine black tea thearubigins
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Weixin Wang, Shuwei Zhang, Lishuang Lv, Shengmin Sang
      Thearubigins (TRs) are the major components of black tea, which are formed during the fermentation reactions. Although anti-inflammatory and anti-cancer activities of TRs have been reported, the prepared TRs according to the literature methods still contain many floating peaks. It is puzzling whether the observed activities are from TRs or these floating peaks. Thus, it is urgent to develop a method to prepare pure TRs and redefine them. In the present study, we developed a new method, the combination of caffeine precipitation and Sephadex LH-20 column chromatography, to prepare pure TRs. The floating peaks on the hump of the crude TRs were removed, and pure TRs were prepared. The chemical profile of the floating peaks was established using LC/MS, and the major compounds in this fraction were identified as apigenin glycosides, quercetin glycosides, kaempferol glycosides, theaflavins, theasinensin, and galloylglucoses based on the analysis of their tandem mass spectra and in comparison with literature data. This study will pave the way to further study the chemistry and biological activities of TRs and the health effects of black tea consumption.

      PubDate: 2018-06-20T06:47:12Z
       
  • Domain contributions to antibody retention in multimodal chromatography
           systems
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Julie Robinson, David Roush, Steve Cramer
      Although a platform process has been established for purification of antibodies, a deep, fundamental understanding of how these molecules interact with chromatography resins has yet to be developed. The increasing prevalence of antibody-related therapeutics and associated purification challenges further motivate research into these molecular level interactions. The objective of this work is to understand the nature (i.e. size and properties) of preferred protein-ligand binding regions for large, multi-domain molecules such as antibodies. In this work, three antibodies with pI 7.5–8.3 and varying hydrophobicity were enzymatically digested to create (Fab)2, Fab, and FC fragments. Linear salt gradient chromatography experiments from 0 to 1M NaCl were carried out with the full mAbs and the fragments in several multimodal chromatography systems at pH 6. The retention of the constituent fragments was then compared to that of the mAb to gain insight into the relative importance of these different domains and the contribution of each domain to the binding of the full mAb in these systems. While some mAbs were dominated by contribution from the FC constant region, others were primarily driven by the (Fab)2 interactions. The domain contributions for each mAb were connected to the unique distribution of surface charge and hydrophobicity using protein surface property maps. This work lays the foundation for identifying the key surface patches on large, multi-domain molecules that are important interaction sites in various multimodal systems. Finally, this work has important implications for the separation of product related variants as well as the design of complex therapeutics for biomanufacturability.

      PubDate: 2018-06-20T06:47:12Z
       
  • A two-step ultra-high-performance liquid chromatography-quadrupole/time of
           flight mass spectrometry with mass defect filtering method for rapid
           identification of analogues from known components of different chemical
           structure types in Fructus Gardeniae-Fructus Forsythiae herb pair extract
           and in rat’s blood
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Wei Zhou, Jinjun Shan, Minxin Meng
      Fructus Gardeniae-Fructus Forsythiae herb pair is an herbal formula used extensively to treat inflammation and fever, but few systematic identification studies of the bioactive components have been reported. Herein, the unknown analogues in the first-step screening were rapidly identified from representative compounds in different structure types (geniposide as iridoid type, crocetin as crocetin type, jasminoside B as monocyclic monoterpene type, oleanolic acid as saponin type, 3-caffeoylquinic acid as organic acid type, forsythoside A as phenylethanoid type, phillyrin as lignan type and quercetin 3-rutinoside as flavonoid type) by UPLC-Q-Tof/MS combined with mass defect filtering (MDF), and further confirmed with reference standards and published literatures. Similarly, in the second step, other unknown components were rapidly discovered from the compounds identified in the first step by MDF. Using the two-step screening method, a total of 58 components were characterized in Fructus Gardeniae-Fructus Forsythiae (FG-FF) decoction. In rat’s blood, 36 compounds in extract and 16 metabolites were unambiguously or tentatively identified. Besides, we found the principal metabolites were glucuronide conjugates, with the glucuronide conjugates of caffeic acid, quercetin and kaempferol confirmed as caffeic acid 3-glucuronide, quercetin 3-glucuronide and kaempferol 3-glucuronide by reference standards, respectively. Additionally, most of them bound more strongly to human serum albumin than their respective prototypes, predicted by Molecular Docking and Simulation, indicating that they had lower blood clearance in vivo and possibly more contribution to pharmacological effects. This study developed a novel two-step screening method in addressing how to comprehensively screen components in herbal medicine by UPLC-Q-Tof/MS with MDF.

      PubDate: 2018-06-20T06:47:12Z
       
  • An enhanced strategy integrating offline two-dimensional separation and
           step-wise precursor ion list-based raster-mass defect filter:
           Characterization of indole alkaloids in five botanical origins of Uncariae
           Ramulus Cum Unicis as an exemplary application
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Huiqin Pan, Changliang Yao, Wenzhi Yang, Shuai Yao, Yong Huang, Yibei Zhang, Wanying Wu, Dean Guo
      Comprehensive chemical profiling is of great significance for understanding the therapeutic material basis and quality control of herbal medicines, which is challenging due to its inherent chemical diversity and complexity, as well as wide concentration range. In this study, we introduced an enhanced strategy integrating offline two-dimensional (2D) separation and the step-wise precursor ion list-based raster-mass defect filter (step-wise PIL-based raster-MDF) scan by tandem LTQ-Orbitrap mass spectrometer. A comprehensive analysis of indole alkaloids in five botanical origins of Uncariae Ramulus Cum Unicis (Gou-Teng) was used as an exemplary application. A positively charged reversed phase (PR) × conventional RP LC system in different pH conditions was constructed with the orthogonality of 74%. A theoretical step-wise PIL among 310–950 Da with the step-size of 2 Da was developed to selectively trigger fragmentations and extend the coverage of potential indole alkaloids. Simultaneously, by defining parent mass width (PMW) of the step-wise PIL to ±55 mDa, a raster-MDF screening was achieved in the acquisition process. Additionally, subtype classification and structural elucidation were facilitated by a four-step interpretation strategy. As a result, a total of 1227 indole alkaloids were efficiently exposed and characterized from five botanical origins of Gou-Teng, which showed high chemical diversity. A systematic comparison among five species was first performed and only 66 indole alkaloids were common. For method validation, three new alkaloid N-oxides were isolated and unambiguously identified by NMR. The present study provides a novel data-dependent acquisition method with improved target coverage and high selectivity. The integrated strategy is practical to efficiently expose and comprehensively characterize complex components in herbal medicines.

      PubDate: 2018-06-20T06:47:12Z
       
  • Online screening of acetylcholinesterase inhibitors in natural products
           using monolith-based immobilized capillary enzyme reactors combined with
           liquid chromatography-mass spectrometry
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Lvhuan Wang, Yumei Zhao, Yanyan Zhang, Tingting Zhang, Jeroen Kool, Govert W. Somsen, Qiqin Wang, Zhengjin Jiang
      In order to develop a direct and reliable method for discovering lead compounds from traditional Chinese medicines (TCMs), a comparative online ligand fishing platform was developed using immobilized capillary enzyme reactors (ICERs) in combination with liquid chromatography-mass spectrometry (LC–MS). Methacrylate-based monolithic capillaries (400 μm I.D. × 10 cm) containing epoxy reactive groups were used as support to immobilize the target enzyme acetylcholinesterase (AChE). The activity and kinetic parameters of the AChE-ICER were investigated using micro-LC-UV. Subsequently, ligand fishing and identification from mixtures was carried out using the complete AChE-ICER-LC–MS platform. For efficient distinction of true actives from false positives, highly automated comparative analyses were run alternatingly using AChE-ICERs and negative control-ICERs, both online installed in the system. After washing unbound compounds to the waste, bound ligands were eluted from the AChE-ICER to a trapping loop using a denaturing solution. The trapped ligands were further separated and identified using LC–MS. Non-specific binding to the monolith support or non-functional sites of the immobilized enzyme was investigated by exposing analytes to the negative control-ICER. The specificity of the proposed approach was verified by analyzing a known AChE inhibitor in the presence of an inactive compound. The platform was applied to screen for AChE inhibitors in extracts of Corydalis yanhusuo. Eight compounds (columbamine, jatrorrhizine, coptisine, palmatine, berberine, dehydrocorydaline, tetrahydropalmatine and corydaline) with AChE binding affinity were detected and identified, and their AChE inhibitory activities were further verified by an in vitro enzymatic inhibition assay. Experimental results show that the proposed comparative online ligand fishing platform is suitable for rapid screening and mass-selective detection of AChE inhibitors in complex mixtures.

      PubDate: 2018-06-20T06:47:12Z
       
  • An improved Ultra-High Performance Liquid chromatography-tandem mass
           spectrometry method for simultaneous quantitation of cytochrome P450
           metabolites of arachidonic acid in human plasma
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Yan Zhang, Meng-Yao Wang, Qi-Yuan Huang, Min-Zhen Zhu, Jing Ren, Xiong Cao, Wen-Chao Xiong, Xiao-Dan Xiao, Xin-Hong Zhu
      This study aims to develop a straightforward, sensitive UHPLC–MS/MS method to quantify 15 eicosanoids derived from arachidonic acid in human plasma. Tert-Butyl methyl ether was used on the liquid–liquid extraction method and significantly reduced the expense and time. The method showed excellent linearity for all analytes, with regression coefficients higher than 0.99 over a wide range of concentrations from 0.01 ng mL−1 to 100 ng mL−1. The recovery rates were over 65.00%, and the matrix effects ranged from 8.42% to 40.00%. The limits of detection ranged from 6 pg mL−1 to 10 pg mL−1, and all of the limits of quantification were 20 − 33 pg mL−1. For the broad concentration range, the RE% for accuracy and precision were less than ± 15%. Moreover, trans-4-{4-[3-(4-Trifluoromethoxyphenyl)-ureido] cyclohexyloxy} benzoic acid (t-TUCB) pretreatment extended the window of detection for as much as 30 days. Eicosanoid signaling is altered in various neurological diseases, including pain, Alzheimer’s disease and major depressive disorder. Therefore, this rapid, robust quantitative profiling of 15 eicosanoids in plasma could provide a distinct eicosanoid fingerprint for precision medicine in these patients.

      PubDate: 2018-06-20T06:47:12Z
       
  • Determination of atmospheric alkylamines by ion chromatography using
           18-crown-6 as mobile phase additive
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Shengqian Zhou, Jing Lin, Xiaofei Qin, Ying Chen, Congrui Deng
      An improved ion chromatographic method including two elution procedures was proposed for the quantitative determination of atmospheric alkylamines in field atmospheric samples involving high levels of inorganic cations by using 18-crown-6 as mobile phase additive. When 18-crown-6 was added to the mobile phase, the retention times increased significantly for Na+, NH4 +, K+ and primary alkylamines but decreased for secondary and tertiary alkylamines due to the complexation with certain cations and interaction with both stationary and mobile phases of 18-crown-6. As a result, the separation of the cations was greatly promoted, which reduced the interference of peak distortion of overloaded inorganic cations on the quantitation of adjacent alkylamines. By using the presented method, five inorganic cations (Na+, NH4 +, K+, Mg2+, Ca2+) and six alkylamines (dimethylamine (DMAH+), trimethylamine + diethylamine (TMAH+ + DEAH+), propylamine (MPAH+), triethylamine (TEAH+), ethanolamine (MEOAH+) and triethanolamine (TEOAH+)) were effectively separated and determined, and the relative standard derivations (RSDs) of objective cations were all less than 1% for retention time and 3.1% for peak area (n = 9), respectively. The linearity was excellent for each cation (R2 > 0.993) except for NH4 + and TEOAH+ showing a non-linear response (R2 > 0.998 for theoretical non-linear fitting), and the detection limit of these cations were 0.03–1.19 ng. The proposed method was successfully used in the determination of both alkylamines and inorganic cations in ambient particulate matters and gaseous alkylamines in ceiling duct exhaust. The annual average concentrations of DMAH+, TMAH+ + DEAH+ and TEAH+ were 15.56, 4.35 and 16.00 ng m−3 in PM2.5 over Shanghai in 2013. The concentrations of gaseous DMA and TMA + DEA in ceiling duct exhaust reached a maximum of 940.0 and 112.7 μg m−3, and were positively correlated with the human activity intensity, suggesting that human excreta emissions was a potential important source of atmospheric alkylamines in urban area of Shanghai.

      PubDate: 2018-06-20T06:47:12Z
       
  • Application of Subwindow Factor Analysis and Mass Spectral information for
           accurate alignment of non-targeted metabolic profiling
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Tian-Biao Yang, Pan Yan, Min He, Liang Hong, Rui Pei, Zhi-Min Zhang, Lun-Zhao Yi, Xin-Ya Yuan
      The peak shifts may lead to an incorrect statistical result for nontargeted metabolomics profiling, such as classification and discrimination in pattern recognition. In the paper, a more accurate alignment algorithm is developed based on Subwindow Factor Analysis and Mass Spectral information (SFA-MS). Compared with other methods, this new algorithm aligns the peaks more accurately without changing their shapes, especially for the overlapping peak clusters. To begin, the Continuous Wavelet Transform with Haar wavelet as the mother wavelet (Haar CWT) is used to determine the position and width of peaks. On this basis, the candidate drift points are confirmed by Fast Fourier Transform (FFT) cross correlation. Furthermore, the MS fitting degree of the common components between the reference chromatogram and the raw chromatogram is determined by the Subwindow Factor Analysis (SFA). When the MS information between reference and raw peaks is identical, the corresponding moving points are the optimum shifts. It is remarkable that all the peaks are moved through linear interpolation in the non-peak parts, so that the aligned chromatograms remain unchanged. The SFA-MS algorithm was implemented in the Matlab language and is available as an open source package.

      PubDate: 2018-06-20T06:47:12Z
       
  • Gas chromatography with simultaneous detection: Ultraviolet spectroscopy,
           flame ionization, and mass spectrometry
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Ronda Gras, Jim Luong, Paul R. Haddad, Robert A. Shellie
      An effective analytical strategy was developed and implemented to exploit the synergy derived from three different detector classes for gas chromatography, namely ultraviolet spectroscopy, flame ionization, and mass spectrometry for volatile compound analysis. This strategy was achieved by successfully hyphenating a user-selectable multi-wavelength diode array detector featuring a positive temperature coefficient thermistor as an isothermal heater to a gas chromatograph. By exploiting the non-destructive nature of the diode array detector, the effluent from the detector was split to two parallel detectors; namely a quadrupole mass spectrometer and a flame ionization detector. This multi-hyphenated configuration with the use of three detectors is a powerful approach not only for selective detection enhancement but also for improvement in structural elucidation of volatile compounds where fewer fragments can be obtained or for isomeric compound analysis. With the diode array detector capable of generating high resolution gas phase spectra, the information collected provides useful confirmatory information without a total dependence on the chromatographic separation process which is based on retention time. This information-rich approach to chromatography is achieved without incurring extra analytical time, resulting in improvements in compound identification accuracy, analytical productivity, and cost. Chromatographic performance obtained from model compounds was found to be acceptable with a relative standard deviation of the retention times of less than 0.01% RSD, and a repeatability at two levels of concentration of 100 and 1000ppm (v/v) of less than 5% (n = 10). With this configuration, correlation of data between the three detectors was simplified by having near identical retention times for the analytes studied.

      PubDate: 2018-06-20T06:47:12Z
       
  • Dedicated comparisons of diverse polysaccharide- and zwitterionic Cinchona
           alkaloid-based chiral stationary phases probed with basic and ampholytic
           indole analogs in liquid and subcritical fluid chromatography mode
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Attila Bajtai, Gyula Lajkó, István Szatmári, Ferenc Fülöp, Wolfgang Lindner, István Ilisz, Antal Péter
      Normal phase (NP) high-performance liquid and sub- and supercritical fluid chromatographic (both acronymed as SFC) methods have been developed for the enantiomer separation of three basic and three ampholytic structurally related C-3-substituted indole analogs on seven non-ionic (neutral) polysaccharide-based and two chemically entirely different zwitterionic Cinchona alkaloid- and sulfonic acid-based chiral stationary phases (CSPs). In a systematic fashion the effect of the composition of the mobile phase, the nature of the alcohol and amine additives on the retention characteristics and enantioselectivity of the ionizable analytes were investigated. On all studied polysaccharide-based CSPs the three ampholytes remained unretained in NP-LC mode, while they were nicely retained and resolved in SFC mode. These unexpected results underline a specific property of liquid CO2 as bulk solvent in combination with alcohols as co-solvents and amine additives thus creating an environment around the chiral selector sites which support the retention of ampholytes. The zwitterionic CSPs worked equally well for the resolution of the basic and ampholytic analytes using a polar ionic mobile phase in both LC and SFC modes. Results acquired by studying the effect of temperature were used to calculate the changes in standard enthalpy Δ(ΔH°), entropy Δ(ΔS°), and free energy Δ(ΔG°) applying van't Hoff plots. The values of the thermodynamic parameters depended on the nature of selectors, the structure of analytes and the properties of the mobile phases. On polysaccharide-based CSPs and columns operated in NP-LC mode enthalpically-, whereas in SFC mode both enthalpically- and entropically-driven enantiomer separations were observed.

      PubDate: 2018-06-20T06:47:12Z
       
  • Electrophoretic focusing on inverse electromigration dispersion gradient.
           The fundamental resolution equation and pressure-assisted performance
           enhancement
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Zdena Malá, Petr Gebauer
      Electrophoretic focusing on inverse electromigration dispersion (EMD) gradient is a new analytical technique based on a unique separation principle where weak non-amphoteric ionogenic species are focused, separated and transported to the detector by an EMD profile of suitable properties. The present work extends the theoretical description of this method by introducing the concept of resolution and deriving the fundamental equation expressing resolution as function of basic system parameters. The results indicate that at constant current operation, resolution is proportional to the square root of time. For variable current regimes (e.g. constant voltage), the time variable is replaced by the product of electric current and passed electric charge. Computer simulations for a model pair of substances support the validity of the presented theory and confirm the theoretical conclusion that resolution can be increased by allowing longer electromigration of the gradient in terms of time or passed charge. The experimental example shown comprises an anionic electrolyte system based on maleic acid and 2,6-lutidine, combined with ESI–MS detection and operated in the reverse mode due to strong electroosmotic flow and ESI suction. The practical implementation of the proposed methodology is done by application of negative pressure at the inlet vial, resulting in very substantial resolution enhancement and baseline separation of otherwise unresolved substances. The performance and high sensitivity of the developed technique is demonstrated on the example of simultaneous analysis of four sulfonamides and three dichlorophenols in waters with limits of detection on the 1 nM level.

      PubDate: 2018-06-20T06:47:12Z
       
  • Poly (N-vinyl imidazole) gel-filled membrane adsorbers for highly
           efficient removal of dyes from water
    • Abstract: Publication date: 17 August 2018
      Source:Journal of Chromatography A, Volume 1563
      Author(s): Fan Hu, Zhanghui Wang, Baoku Zhu, Liping Zhu, Youyi Xu
      Energy-efficient and time-saving process for recovery of hazardous dyes from wastewater is highly desired in dyeing industry. In this work, poly(N-vinyl imidazole) (PVI) gel-filled membrane adsorbers were developed for highly efficient recovery of dyes through adsorption filtration. The membrane adsorbers were fabricated via dip-coating of Nylon macroporous membranes in PVI solutions followed by quaternization crosslinking with p-xylylene dichloride (XDC). Physicochemical characterizations indicated that PVI gel was successfully filled and fixed inside the Nylon matrix. In optimized conditions. The treating capacity of membrane adsorbers to typical dye sunset yellow (25 ppm of the feed concentration) reached up to 197 mg/g with the removal ratio >99%. Both the treating capacity and the removal ratio were kept steady even when the permeation flux was as high as 1000 L/m2 h. The membrane adsorbers developed in this work were able to not only remove anionic dyes from water, but also separate anionic dyes from cationic ones. The zeta potential and adsorption tests showed that the electrostatic interaction between PVI gel and dye molecules was responsible for the high removal efficiencies to anionic dyes. The membrane adsorbers can be regenerated effectively with NaOH solution and demonstrated good stability in both acidic and alkaline conditions.

      PubDate: 2018-06-20T06:47:12Z
       
  • Screening and identification of ligand-protein interactions using
           functionalized heat shock protein 90-fluorescent mesoporous silica-indium
           phosphide/zinc sulfide quantum dot nanocomposites
    • Abstract: Publication date: 10 August 2018
      Source:Journal of Chromatography A, Volume 1562
      Author(s): Zhaoyi Miao, Yue Hu, Xiaojing Zhang, Xiaotong Yang, Yingying Tang, An Kang, Dong Zhu
      Currently, nanosphere-based ligand fishing cannot be accomplished with imaging processing, although this step is important for real-time identification. Herein, a ligand fishing technique combined with real-time imaging is presented for the identification of ligands for heat shock protein 90α (Hsp 90α) from a complex matrix, Alisma plantago-aquatica Linn. crude extract, using Hsp 90α-functionalized mesoporous silica nanoparticle (MSN)-InP/ZnS quantum dot (QD) nanocomposites as a support material. Twenty ligands for Hsp 90α were screened, and their structures were identified by mass spectrometry. The activities of the ligands were verified by real-time imaging of cells apoptotic morphological changes. Quantitative analysis showed that Alisma plantago-aquatica Linn contained 8.19μg/g Alisol F, which regarded as one typical component of Alisma plantago-aquatica Linn, and the extraction ratio of Alisol F was 76.2%. The precision for five replicate measurements was 7.0% (RSD). The prepared nanocomposites were also used to screen proteins from a mixture of cellular extracts, and five proteins from HeLa cells were identified as potential client proteins of Hsp 90α.

      PubDate: 2018-06-17T10:31:45Z
       
  • Sequence-specific sepsis-related DNA capture and fluorescent labeling in
           monoliths prepared by single-step photopolymerization in microfluidic
           devices
    • Abstract: Publication date: 10 August 2018
      Source:Journal of Chromatography A, Volume 1562
      Author(s): Radim Knob, Robert L. Hanson, Olivia B. Tateoka, Ryan L. Wood, Israel Guerrero-Arguero, Richard A. Robison, William G. Pitt, Adam T. Woolley
      Fast determination of antibiotic resistance is crucial in selecting appropriate treatment for sepsis patients, but current methods based on culture are time consuming. We are developing a microfluidic platform with a monolithic column modified with oligonucleotides designed for sequence-specific capture of target DNA related to the Klebsiella pneumoniae carbapenemase (KPC) gene. We developed a novel single-step monolith fabrication method with an acrydite-modified capture oligonucleotide in the polymerization mixture, enabling fast monolith preparation in a microfluidic channel using UV photopolymerization. These prepared columns had a threefold higher capacity compared to monoliths prepared in a multistep process involving Schiff-base DNA attachment. Conditions for denaturing, capture and fluorescence labeling using hybridization probes were optimized with synthetic 90-mer oligonucleotides. These procedures were applied for extraction of a PCR amplicon from the KPC antibiotic resistance gene in bacterial lysate obtained from a blood sample spiked with E. coli. The results showed similar eluted peak areas for KPC amplicon extracted from either hybridization buffer or bacterial lysate. Selective extraction of the KPC DNA was verified by real time PCR on eluted fractions. These results show great promise for application in an integrated microfluidic diagnostic system that combines upstream blood sample preparation and downstream single-molecule counting detection.

      PubDate: 2018-06-17T10:31:45Z
       
  • Fast and high-efficiency magnetic surface imprinting based on
           microwave-accelerated reversible addition fragmentation chain transfer
           polymerization for the selective extraction of estrogen residues in milk
    • Abstract: Publication date: 10 August 2018
      Source:Journal of Chromatography A, Volume 1562
      Author(s): Fangfang Chen, Jiayu Wang, Ruicong Lu, Huiru Chen, Xiaoyu Xie
      A novel microwave-accelerated reversible addition fragmentation chain transfer (RAFT) polymerization strategy has been introduced to shorten reaction time and improved polymerization efficiency of the conventional molecularly imprinting technology based on RAFT. Magnetic molecular imprinted polymers (MMIPs) were successfully synthesized much more efficiently using 17β-estradiol (E2) as a template for the determination of estrogen residues. The resultant MMIPs had well-defined thin imprinted film, favoring the fast mass transfer. Moreover, the reaction time, which was just 1/24 of the time taken by conventional heating, was significantly decreased, improving the reaction efficiency and reducing the probability of side reactions. Meanwhile, the obtained polymers have good capacity of 6.67 mg g−1 and satisfactory selectivity to template molecule with the imprinting factor of 5.11. As a result, a method combination of the resultant MMIPs as solid phase extraction sorbents and high-performance liquid chromatography was successfully set up to determinate three estrogen residues in milk samples. For E2, estrone, and estriol, the limit of detections were calculated to be 0.03, 0.08, and 0.06 ng mL−1, respectively, and the limit of quantifications were 0.11, 0.27, and 0.21 ng mL−1, respectively. At the spiked level of 1, 5, and 10 ng mL−1, the recoveries of the three estrogens were ranged from 69.1% to 91.9% and the intra-day relative standard deviation (RSD) was less than 5.7%. In addition, the resultant MMIPs exhibited good reproducibility and reusability with the inter-batch RSD of 5.3% and the intra-batch RSD of 6.2%, respectively. Overall, the realization of this strategy facilitates the preparation of MMIPs with good architecture and high reaction efficiencies for the analysis of complicated real samples.

      PubDate: 2018-06-17T10:31:45Z
       
  • Multi-residue pesticide analysis in virgin olive oil by nanoflow liquid
           chromatography high resolution mass spectrometry
    • Abstract: Publication date: 10 August 2018
      Source:Journal of Chromatography A, Volume 1562
      Author(s): David Moreno-González, Jaime Alcántara-Durán, Silvina M. Addona, Miriam Beneito-Cambra
      In this article, a nanoflow liquid chromatography system coupled to high resolution mass spectrometry (nanoflow LC/ESI Q-Orbitrap-MS) has been applied for the development of a multiresidue pesticide method for the determination of 162 multiclass pesticides in olive oil samples. Due to the relatively high lipid content of the raw QuEChERS acetonitrile extracts obtained from this type of fatty vegetable samples, a dispersive solid phase extraction (dSPE) sorbent proposed to retain both fatty acids and triglycerides, namely Enhanced Matrix Removal-Lipid (EMR-Lipid) has been implemented as additional cleanup step. The analytical performances of the proposed method were evaluated,achieving recoveries in the range 75–119% with relative standard deviations lower than 19% (n = 6). The dSPE sorbent allowed the removal of most coextracted interferences without a significant loss of analytes. Matrix effects were also evaluated, showing a negligible effect for most of the compounds tested, when a dilution factor of 50 was applied. Notably, despite the use of relatively high dilution factors (e.g. 1:50) to minimize matrix effects, the lowest concentration levels detected with this method – in the low μg kg−1 range – are well below the corresponding maximum residue levels established by the current European legislation.

      PubDate: 2018-06-17T10:31:45Z
       
  • Development and validation of a QuEChERS method for the analysis of
           5-nitroimidazole traces in infant milk-based samples by ultra-high
           performance liquid chromatography-tandem mass spectrometry
    • Abstract: Publication date: 10 August 2018
      Source:Journal of Chromatography A, Volume 1562
      Author(s): Maykel Hernández-Mesa, Ana M. García-Campaña, Carmen Cruces-Blanco
      QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) methodology in combination with UHPLC–MS/MS is proposed for the determination of 5-nitroimidazole (5-NDZ) residues in infant milk-based products. Chromatographic separation was accomplished in a C18 Zorbax Eclipse Plus RRHD (50 × 2.1 mm, 1.8 μm) column under gradient elution conditions. Mobile phase consisted of 0.025% (v/v) aqueous formic acid (eluent A) and MeOH (eluent B), and was supplied at a flow rate of 0.5 mL/min. Under these conditions, eleven 5-NDZs including three metabolites were separated in less than 4 min. A novel QuEChERS method was optimized, and primary-secondary amine (PSA) sorbent was selected as clean-up agent. In addition, the proposed QuEChERS procedure was compared with other sample preparation methodologies, which are usually used in the analysis of 5-NDZs, namely solid phase extraction (SPE) using mixed cation exchange (MCX) cartridges and molecularly imprinted solid phase extraction (MISPE). Method comparison was carried out in terms of process efficiency, which includes matrix effect and extraction recovery. Higher process efficiency was generally achieved for QuEChERS and MISPE than for SPE. However, matrix effect was more significant for the non-selective QuEChERS method than for the selective MISPE. Higher extraction recoveries (63.2–94.1%) were observed for QuEChERS. The studied methods were validated in terms of linearity, detection limits (CCα), detection capabilities (CCβ) and precision, observing similar performance characteristics independently of the proposed sample treatment. CCα and CCβ ranged between 0.05 and 1.69 μg/L for all analytes and extraction techniques. QuEChERS-UHPLC–MS/MS method was also validated in terms of precision (relative standard deviations <10.3%), trueness (recovery>70.2%) and selectivity according to Regulation 2002/657/EC. It is proposed as a good alternative for the monitoring of 5-NDZ residues in enriched infant-milk based products and other similar milk based-products.

      PubDate: 2018-06-17T10:31:45Z
       
  • Model-based design of an intermittent simulated moving bed process for
           recovering lactic acid from ternary mixture
    • Abstract: Publication date: 10 August 2018
      Source:Journal of Chromatography A, Volume 1562
      Author(s): Mingkai Song, Linlin Cui, Han Kuang, Jingwei Zhou, Pengpeng Yang, Wei Zhuang, Yong Chen, Dong Liu, Chenjie Zhu, Xiaochun Chen, Hanjie Ying, Jinglan Wu
      An intermittent simulated moving bed (3F-ISMB) operation scheme, the extension of the 3W-ISMB to the non-linear adsorption region, has been introduced for separation of glucose, lactic acid and acetic acid ternary-mixture. This work focuses on exploring the feasibility of the proposed process theoretically and experimentally. Firstly, the real 3F-ISMB model coupled with the transport dispersive model (TDM) and the Modified-Langmuir isotherm was established to build up the separation parameter plane. Subsequently, three operating conditions were selected from the plane to run the 3F-ISMB unit. The experimental results were used to verify the model. Afterwards, the influences of the various flow rates on the separation performances were investigated systematically by means of the validated 3F-ISMB model. The intermittent-retained component lactic acid was finally obtained with the purity of 98.5%, recovery of 95.5% and the average concentration of 38 g/L. The proposed 3F-ISMB process can efficiently separate the mixture with low selectivity into three fractions.

      PubDate: 2018-06-17T10:31:45Z
       
  • Isolation of biofunctional bovine immunoglobulin G from milk- and
           colostral whey with mixed-mode chromatography at lab and pilot scale
    • Abstract: Publication date: 10 August 2018
      Source:Journal of Chromatography A, Volume 1562
      Author(s): Hans-Jürgen Heidebrecht, Bernadette Kainz, Roland Schopf, Klaus Godl, Züleyha Karcier, Ulrich Kulozik, Beatrix Förster
      The aim of the present work was to develop a new scalable and cost-efficient process to isolate bovine immunoglobulin G from colostral whey with high purity and minimal loss of activity. The mixed mode material Mercapto-Ethyl-Pyridine-Hypercel™ was identified appropriate for direct capture of immunoglobulin G. The binding mechanism is primarily based on hydrophobic interactions at physiological conditions. As compared to immunoglobulin G, all other low molecular whey proteins such as α-Lactalbumin or β-Lactoglobulin, except lactoperoxidase, are more hydrophilic and were therefore found in the flow-through fraction. In order to remove lactoperoxidase as an impurity the column was combined in series with a second mixed mode material (Capto™- with N-benzoyl-homocysteine as ligand) using the same binding conditions. At pH 7.5 the carboxyl group of this ligand is negatively charged and can hence bind the positively charged lactoperoxidase, whose isoelectric point is at pH 9.6. After sample application, the columns were eluted separately. By combining the two columns it was possible to obtain immunoglobulin G with a purity of >96.1% and yield of 65–80%. The process development was carried out using 1 mL columns and upscaling was performed in three steps up to a column volume of 8800 mL for the Hypercel™ column and 3000 mL for the Capto™- column. At this scale it is possible to obtain 130–150 g pure immunoglobulin G from 3 L colostrum within five hours, including the regeneration of both columns. Additionally, the impact of freeze-drying on the isolated immunoglobulin G was studied. The nativity of the freeze dried immunoglobulin was above 95%, which was proven by reversed phase liquid chromatography and validated by differential scanning calorimetry. The activity of immunoglobulin G was preserved over the isolation process and during drying as measured by enzyme-linked immunosorbent assay. In conclusion, by applying the proposed isolation process, it becomes feasible to obtain pure, active and stable imunnunoglobulin G at large scale.

      PubDate: 2018-06-17T10:31:45Z
       
  • Enantioselective multiple heartcut two-dimensional ultra-high-performance
           liquid chromatography method with a Coreshell chiral stationary phase in
           the second dimension for analysis of all proteinogenic amino acids in a
           single run
    • Abstract: Publication date: 10 August 2018
      Source:Journal of Chromatography A, Volume 1562
      Author(s): Ulrich Woiwode, Stefan Neubauer, Wolfgang Lindner, Stephan Buckenmaier, Michael Lämmerhofer
      A multiple heartcut (MHC) 2D-UHPLC method with UV detection has been developed for the enantioselective analysis of complex amino acid mixtures in a single run. The MHC method is based on an achiral gradient RPLC separation with 1.8 μm C18 phase (100 × 2.1 mm ID column) in the first dimension (1D) and enantioselective isocratic separation on a tert-butylcarbamoylquinine-based 2.7 μm Coreshell particle column (50 × 3 mm ID) in the second dimension (2D). Pre-column derivatization has been performed with Sanger’s reagent (2,4-dinitrofluorobenzene) yielding chromogenic 2,4-dinitrophenylated amino acids (DNP-AAs). Heartcuts of 40 μL fractions of the 1D peaks were sampled into the 2D system via a two-position four-port dual valve connected to two loop decks each equipped with six 40 μL parking loops. Using this setup, 25 amino acids (20 proteinogenic plus allo-Thr, allo-Ile, homoserine (Hse), Orn, β-Ala) have been analyzed enantioselectively in a fully automated manner with a single chiral column within 130 min total run time (1D and 2D). All 2D separations together took 101.5 min (29 cuts with 3.5 min run time each) and thus the total analysis time was quite efficiently utilized. Faster separations were restricted by some software constraints which did not allow to adjust run times in 2D individually. The practical utility of this enantioselective MHC method is documented by application for the absolute configuration determination of the amino acids in gramicidin and bacitracin. Further optimizations should lead to a generic enantioselective amino acid analyzer for the quality control of synthetic peptides and the structural characterization of non-ribosomal peptides.

      PubDate: 2018-06-17T10:31:45Z
       
  • Evaluation of active solvent modulation to enhance two-dimensional liquid
           chromatography for target analysis in polymeric matrices
    • Abstract: Publication date: 10 August 2018
      Source:Journal of Chromatography A, Volume 1562
      Author(s): Matthias Pursch, Antje Wegener, Stephan Buckenmaier
      A new methodology is presented for two-dimensional liquid chromatography (2D-LC) separations of polymers. Active solvent modulation (ASM) was evaluated in its effectiveness to enhance solvent compatibility for both separation dimensions. As an example the determination of target compounds in epoxy resins was used. Ultra-high pressure size-exclusion chromatography was applied in the first dimension using THF as the solvent. The second dimension separation was operated in reversed-phase mode using an acetonitrile/water gradient. ASM prevents sample breakthrough in the second dimension and produces chromatograms that are of great peak shape and high resolution. It enables very sensitive determination of target components down to the low ppm level. The resulting high-speed 2D-LC method (10 min analysis time) showed good linearity (R2 > 0.9995) and reproducibility (as low as 0.3–0.7% peak area RSD). ASM was also applied in comprehensive 2D-LC (SECxLC) mode for characterization of molecular weight and chemical composition distribution of a polymer blend consisting of epoxy novolac and phenol novolac. The SECxLC separation was executed at short run times (20 min). ASM technology can markedly enhance productivity in 2D-LC analysis for many complex sample matrices.

      PubDate: 2018-06-17T10:31:45Z
       
  • Core microstructure, morphology and chain arrangement of block copolymer
           self-assemblies as investigated by thermal field-flow fractionation
    • Abstract: Publication date: 10 August 2018
      Source:Journal of Chromatography A, Volume 1562
      Author(s): U.L. Muza, G. Greyling, H. Pasch
      The self-assembly of block copolymers (BCPs), as a result of solvent selectivity for one block, has recently received significant attention due to novel applications of BCPs in pharmaceuticals, biomedicine, cosmetics, electronics and nanotechnology. The correlation of BCP microstructure and the structure of the resulting self-assemblies requires advanced analytical methods. However, traditional bulk characterization techniques are limited in the quest of providing detailed information regarding molar mass (Mw), hydrodynamic size (Dh), chemical composition, and morphology for these self-assemblies. In the present study, thermal field-flow fractionation (ThFFF) is utilised to investigate the impact of core microstructure on the resultant solution properties of vesicles prepared from polystyrene-polybutadiene block copolymers (PS-b-PBd) with 1.2- and 1.4-polybutadiene blocks, respectively. As compared to investigations on the impact of the corona microstructure, the impact of core microstructure on micellar properties has largely been neglected in previous work. In N,N-dimethylacetamide (DMAc) these BCPs form vesicles having PS shells and PBd cores. Dh, Mw, aggregation number, and critical micelle concentration of these micelles are shown to be sensitive to the core microstructure, therefore, demonstrating the potential of microstructural differences to be used for providing tuneable pathways to specific self-assemblies. It is shown that micelles prepared from BCPs of similar PS and PBd block sizes are successfully separated by ThFFF. It is further demonstrated in this study that PS-b-PBd vesicles and PS homopolymers of identical surface chemistry (PS) and comparable Dh in DMAc, can be separated by ThFFF.

      PubDate: 2018-06-17T10:31:45Z
       
  • Applicability of supercritical fluid chromatography – mass spectrometry
           to metabolomics. I – Optimization of separation conditions for the
           simultaneous analysis of hydrophilic and lipophilic substances
    • Abstract: Publication date: 10 August 2018
      Source:Journal of Chromatography A, Volume 1562
      Author(s): Vincent Desfontaine, Gioacchino Luca Losacco, Yoric Gagnebin, Julian Pezzatti, William P. Farrell, Víctor González-Ruiz, Serge Rudaz, Jean-Luc Veuthey, Davy Guillarme
      The aim of this study was to evaluate the suitability of SFC-MS for the analysis of a wide range of compounds including lipophilic and highly hydrophilic substances (log P values comprised between −6 and 11), for its potential application toward human metabolomics. For this purpose, a generic unified chromatography gradient from 2 to 100% organic modifier in CO2 was systematically applied. In terms of chemistry, the best stationary phases for this application were found to be the Agilent Poroshell HILIC (bare silica) and Macherey-Nagel Nucleoshell HILIC (silica bonded with a zwitterionic ligand). To avoid system overpressure at very high organic modifier proportion, columns of 100 × 3 mm I.D. packed with sub-3 μm superficially porous particles were selected. In terms of organic modifier, a mixture of 95% MeOH and 5% water was selected, with 50 mM ammonium formate and 1 mM ammonium fluoride, to afford good solubility of analytes in the mobile phase, limited retention for the most hydrophilic metabolites and suitable peak shapes of ionizable species. A sample diluent containing 50%ACN/50% water was employed as injection solvent. These conditions were applied to a representative set of metabolites belonging to nucleosides, nucleotides, small organic acids, small bases, sulfated/sulfonated metabolites, poly-alcohols, lipid related substances, quaternary ammonium metabolites, phosphate-based substances, carbohydrates and amino acids. Among all these metabolites, 65% of the compounds were adequately analyzed with excellent peak shape, 23% provided distorted peak shapes, while only 12% were not detected (mostly metabolites having several phosphate or several carboxylic acid groups).

      PubDate: 2018-06-17T10:31:45Z
       
  • Designing flexible low-viscous sieving media for capillary electrophoresis
           analysis of ribonucleic acids
    • Abstract: Publication date: 10 August 2018
      Source:Journal of Chromatography A, Volume 1562
      Author(s): Louis De Scheerder, Anders Sparén, Gunilla A. Nilsson, Per-Ola Norrby, Eivor Örnskov
      Modified messenger RNA (mRNA) has recently become a new prospective class of drug product. Consequently, stability indicating separation methods are needed to progress pharmaceutical development of mRNA. A promising separation technique for the analysis of mRNA is capillary gel electrophoresis (CGE). We designed a flexible, low-viscous sieving medium for CGE, based on high mass linear polyvinylpyrrolidone (PVP) and glycerol. A Central Composite Face-centered design resulted in a strong model that allowed us to predict suitable sieving media compositions by using multi-objective optimization. The way of working proposed in this paper gives analysts the freedom to design a suitable sieving medium for their response(s) of interest, for purity and stability analysis of polynucleotides with a size around 100–1000 bases. Depending on the criteria for the analysis there will be a trade-off between different suitable conditions. By using this method, we created a sieving medium that was able to improve resolution, peak height and analysis time of an RNA ladder compared to the current commercially available separation gels.

      PubDate: 2018-06-17T10:31:45Z
       
  • Chiral analysis of theanine and catechin in characterization of green tea
           by cyclodextrin-modified micellar electrokinetic chromatography and high
           performance liquid chromatography
    • Abstract: Publication date: 10 August 2018
      Source:Journal of Chromatography A, Volume 1562
      Author(s): Jessica Fiori, Benedetta Pasquini, Claudia Caprini, Serena Orlandini, Sandra Furlanetto, Roberto Gotti
      Monomeric catechins are important compounds in green tea accounting for potential bioactivity against a wide range of diseases. Besides catechins, l-Theanine (γ-glutamylethylamide), a characteristic amino acid in tea leaves, has become a further focus of the phytochemical research for the reported beneficial effects mainly on cognitive performance, emotional state and sleep quality. In the present study has been developed a CD-MEKC method based on sodium dodecyl sulfate (SDS) and Heptakis (2,6-di-O-methyl)-β-cyclodextrin for the separation of six major green tea catechins and enantiomers of theanine. The latter, because of the poor detectability was derivatized prior analysis by o-phthaldialdehyde in the presence of N-acetyl-l-cysteine which, under mild conditions (neutral pH, in two minutes) allowed two diastereomers isoindole derivatives to be obtained. The derivatization reaction was directly carried out on tea infusion and derivatized samples were analysed by CD-MEKC involving 65 mM SDS and 28 mM cyclodextrin in acidic buffer (pH 2.5). The separation of six major green tea catechins including enantioresolution of (±)-Catechin and d/l-Theanine was obtained in about 5 min allowing d-Theanine to be quantified at least at 0.5% m/m level with respect to l-Theanine. Since (−)-Catechin and d-Theanine can be considered as non-native enantiomers (distomers), their presence in real samples provides an indication of tea leaves treatments (thermal treatment, fermentation, etc.) and could represent an opportunity for grading tea. The obtained results were confirmed by a RP-HPLC approach; even though the chromatography was developed in achiral conditions, the derivatization approach applied to theanine (diastereomers formation), allowed for d/l-Theanine chiral analysis.

      PubDate: 2018-06-17T10:31:45Z
       
  • Validation of an analytical method for 1,2,4-triazole in soil using liquid
           chromatography coupled to electrospray tandem mass spectrometry and
           monitoring of propiconazole degradation in a batch study
    • Abstract: Publication date: 10 August 2018
      Source:Journal of Chromatography A, Volume 1562
      Author(s): A. Blondel, B. Krings, N. Ducat, O. Pigeon
      1,2,4-triazole is one of the most important metabolites resulting from the degradation of a large class of pesticides, the triazole fungicides. These fungicides are widely used on fruits, vegetables and cereals. Two different analytical methods which are quick, cheap and easy to implement were developed and validated to monitor propiconazole and 1,2,4-triazole in soil using LC–MS/MS. The limits of quantification reached were 4.0 μg kg−1 for propiconazole and 1.1 μg kg−1 for 1,2,4-triazole. The recovery range was from 93 to 99% with a relative standard deviation <11.2% and from 83 to 97% with a RSD <7.8% for propiconazole and 1,2,4-triazole respectively. These methods: were used to monitor the degradation of propiconazole and the formation of 1,2,4-triazole in soil in a batch study lasting 28 days.

      PubDate: 2018-06-17T10:31:45Z
       
  • Tunable normal phase enantioselectivity of amino acid esters via mobile
           phase composition
    • Abstract: Publication date: 10 August 2018
      Source:Journal of Chromatography A, Volume 1562
      Author(s): Alice Yang, Jonathan G. Shackman, Yun K. Ye
      The ability to tune chiral selectivity through mobile phase modifiers is a powerful tool in chiral separations. Beyond improving efficiency and/or resolution, some mobile phase systems can even invert elution order, a highly desirable result for trace analyses or preparative scale isolations. Previous work has demonstrated that acidic modifiers, such as ethanesulfonic acid (ESA), can greatly impact separations of enantiomers. However, prior studies were primarily performed on coated chiral stationary phases (CSPs), which limited the selection of the bulk mobile phase component. In this work, the effect of ESA modifier was studied for the enantioseparation of six pairs of amino acid esters on a CHIRALPAK® IA column, an immobilized amylose-based CSP, with different combinations of standard solvents (hexane and ethanol) as well as “non-standard” solvents, such as methyl t-butyl ether, ethyl acetate, tetrahydrofuran, acetone, or 1,4-dioxane. ESA generally improved selectivity, and multiple instances of elution order reversal were observed. A Van Deemter plot study reveals that ESA exerts its effect by pulling the enantiomer deeper into the chiral cavity of the chiral polymer to increase the interactions between the analytes and the stationary phase, which is the main reason for the increased enantioselectivity.

      PubDate: 2018-06-17T10:31:45Z
       
 
 
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