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Journal Cover Journal of Chromatography A
  [SJR: 1.774]   [H-I: 184]   [126 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0021-9673
   Published by Elsevier Homepage  [3123 journals]
  • Dendritic core-shell silica spheres with large pore size for separation of
           biomolecules
    • Authors: Qishu Qu; Yang Si; Han Xuan; Kehua Zhang; Xiaoming Chen; Yi Ding; Shaojie Feng; Han-Qing Yu
      Pages: 40 - 42
      Abstract: Publication date: Available online 4 February 2018
      Source:Journal of Chromatography A
      Author(s): Qishu Qu, Yang Si, Han Xuan, Kehua Zhang, Xiaoming Chen, Yi Ding, Shaojie Feng, Han-Qing Yu, M. Asiri Abdullah, Khalid A. Alamry
      Monodispersed core-shell silica spheres with fibrous shell structure and tunable pore size were prepared by using a one-pot oil-water biphase method. The pore size could be tuned from 7 nm to 37 nm by using organic solvents with different polarities as oil phase. The spheres synthesized by using benzene as organic solvent had the maximum pore size of 37 nm and possessed a surface area of 61 m2 g−1. The obtained wide pore core-shell silica spheres were applied for rapidly separating small molecules, peptides, small proteins, and large proteins with molecular weight up to 200 kDa. Since the pore size of the core-shell silica spheres was sufficiently large for the free access of all the solutes, sharp and symmetric peaks were obtained. The separation performance was as high as 264531 plates m−1 for fluorene. The great efficient separation demonstrates that the wide pore core-shell silica spheres have a great potential for rapid analysis of both small and large solutes with high performance liquid chromatography.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.matlet.2017.09.087
      Issue No: Vol. 211 (2018)
       
  • Functionalized metal-organic framework nanocomposites for dispersive solid
           phase extraction and enantioselective capture of chiral drug intermediates
           
    • Authors: Xue Ma; Xiaohua Zhou; Ajuan Yu; Wuduo Zhao; Wenfen Zhang; Shusheng Zhang; Linlin Wei; Debra J. Cook; Anirban Roy
      Pages: 1 - 9
      Abstract: Publication date: 16 February 2018
      Source:Journal of Chromatography A, Volume 1537
      Author(s): Xue Ma, Xiaohua Zhou, Ajuan Yu, Wuduo Zhao, Wenfen Zhang, Shusheng Zhang, Linlin Wei, Debra J. Cook, Anirban Roy
      The facile preparation, characterization and application of a novel magnetic graphene oxide- metal organic framework [Zn2(d-Cam)2(4, 4′-bpy)]n (MGO-ZnCB) as a sorbent for fast, simple and enantioselective capture of chiral drug intermediates are presented in this paper. The MGO-ZnCB nanocomposite, developed by encapsulating MGO nanoparticles into the homochiral metal organic framework of ZnCB, can integrate the advantages from each component endowing the hybrids with improved synergystic effects. The enantioselective performance of MGO-ZnCB was evaluated by dispersive magnetic nanoparticle solid phase extraction (d-MNSPE) of 1, 1′-bi-2-naphthol (BN) and 2, 2′-furoin (Furoin) racemic solutions. Due to the excellent dispersive capability, high stability, relatively larger saturation magnetization and distinct enrichment capacity of MGO-ZnCB, the d-MNSPE method provids good enantioselective separation of these compounds with enantiomeric excess (ee) values as high as 74.8% and 57.4%, respectively. The entire process with BN or Furoin can be completed within 3 min or less. After washing with methanol, the host MGO-ZnCB can be easily recycled and reused six times without any apparent loss of performance. Furthermore, the adsorbed BN and Furoin in nanodomains of the MGO-ZnCB composite were directly investigated for the first time by atomic force microscopy-infrared (AFM-IR) technique.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.12.067
      Issue No: Vol. 1537 (2018)
       
  • Miniaturized solid-phase extraction of macrolide antibiotics in honey and
           bovine milk using mesoporous MCM-41 silica as sorbent
    • Authors: Li-Jing Du; Ling Yi; Li-Hong Ye; Yu-Bo Chen; Jun Cao; Li-Qing Peng; Yu-Ting Shi; Qiu-Yan Wang; Yu-Han Hu
      Pages: 10 - 20
      Abstract: Publication date: 16 February 2018
      Source:Journal of Chromatography A, Volume 1537
      Author(s): Li-Jing Du, Ling Yi, Li-Hong Ye, Yu-Bo Chen, Jun Cao, Li-Qing Peng, Yu-Ting Shi, Qiu-Yan Wang, Yu-Han Hu
      A simple and effective method of miniaturized solid-phase extraction (mini-SPE) was developed for the simultaneous purification and enrichment of macrolide antibiotics (MACs) (i.e. azithromycin, clarithromycin, erythromycin, lincomycin and roxithromycin) from honey and skim milk. Mesoporous MCM-41 silica was synthesized and used as sorbent in mini-SPE. Several key parameters affecting the performance of mini-SPE procedure were thoroughly investigated, including sorbent materials, amount of sorbent and elution solvents. Under the optimized condition, satisfactory linearity (r2 > 0.99), acceptable precision (RSDs, 0.3–7.1%), high sensitivity (limit of detection in the range of 0.01–0.76 μg/kg), and good recoveries (83.21–105.34%) were obtained. With distinct advantages of simplicity, reliability and minimal sample requirement, the proposed mini-SPE procedure coupled with ultrahigh performance liquid chromatography and quadrupole time-of-flight tandem mass spectrometry could become an alternative tool to analyze the residues of MACs in complex food matrixes.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2018.01.005
      Issue No: Vol. 1537 (2018)
       
  • Microwave-assisted decomplexation and in-situ headspace in-syringe dynamic
           derivatization of dimethylamine borane with high performance liquid
           chromatography-fluorescence detection
    • Authors: Sarangapani Muniraj; Hua-Kwang Lee; Chunming Hsiech; Jen-Fon Jen
      Pages: 21 - 26
      Abstract: Publication date: 16 February 2018
      Source:Journal of Chromatography A, Volume 1537
      Author(s): Sarangapani Muniraj, Hua-Kwang Lee, Chunming Hsiech, Jen-Fon Jen
      A rapid, sensitive, selective, and simple method for monitoring dimethylamine borane (DMAB) in aqueous sample is proposed by combining microwave-assisted de-complexation, headspace liquid phase in-situ derivatization extraction, and high-performance liquid chromatography-fluorescence detection for the determination of DMAB in samples. The present procedure involves de-complexation of DMAB using microwave irradiation, evolution of dimethylamine (DMA) to the headspace from an alkalized sample solution, and dynamic headspace liquid-phase derivatization extraction (Dy-HS-LPDE) of DMA with 9-fluorenylmethyl chloroformate in a syringe barrel. In addition to the optimal Dy-HS-LPDE and chromatographic parameters described in our previous study, the de-complexation of DMAB by thermal and microwave-assisted procedures and evolution of DMA into the headspace from an alkalized solution and modification of the Dy-HS-LPDE method are thoroughly investigated. The results indicate that complete de-complexation was obtained at 70 °C for 5 min, 30 °C for 10 min, or using microwave irradiation for 30 s at any applied power. It indicates that the DMAB complex easily undergoes de-complexation under microwave irradiation. The linearity range was 0.01–0.5 mg L−1 for DMAB and 0.0077–0.38 mg L−1 for DMA, with a coefficient of determination of 0.9995, and limit of detection of 3 μg L−1 (limit of quantitation of 10 μg L−1) for DMAB. The recoveries of DMAB are 95.3% (3.0% RSD) for waste water when spiked 0.05 mg L−1 and 93.5% (5.4% RSD) for the samples spiked with copper and nickel salts (5 mM each in the spiked waste sample). The whole analytical procedure can be completed within 25 min. The results confirm that the present method is a rapid, sensitive, selective, automated, low-cost and eco-friendly procedure to identify DMAB in samples.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2018.01.012
      Issue No: Vol. 1537 (2018)
       
  • Analysis of four sulfonylurea herbicides in cereals using modified Quick,
           Easy, Cheap, Effective, Rugged, and Safe sample preparation method coupled
           with liquid chromatography–tandem mass spectrometry
    • Authors: Yanxia Ni; Huan Yang; Hantong Zhang; Qiao He; Siqi Huang; Meiling Qin; Shuangshuang Chai; Huanhuan Gao; Youning Ma
      Pages: 27 - 34
      Abstract: Publication date: 16 February 2018
      Source:Journal of Chromatography A, Volume 1537
      Author(s): Yanxia Ni, Huan Yang, Hantong Zhang, Qiao He, Siqi Huang, Meiling Qin, Shuangshuang Chai, Huanhuan Gao, Youning Ma
      A modified Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) sample preparation method, coupled with liquid chromatography-electrospray ionization tandem mass spectrometry, has been developed for the simultaneous analysis of four commonly used sulfonylurea herbicides, ethoxysulfuron, halosulfuron-methyl, mesosulfuron-methyl and orthosulfamuron, in rice, maize, wheat and soybean. Adsorption of the analytes onto the primary-secondary amine used in the clean-up step was avoided by using 1% formic acid in acetonitrile as the extraction solvent to maintain the acidic herbicides in a non-ionized state. Trueness studies were carried out at three levels (2.5, 25 and 250 μg/kg for ethoxysulfuron and 5, 50 and 500 μg/kg for the other three analytes). Promising trueness (70.2%–119.8%) was achieved for all herbicides in all matrices after clean-up, with relative standard deviations (RSDr) < 18.6%. Satisfactory matrix effects (−19.7% to 14.8%) were also obtained. Good linearity of the calibration curves was achieved, with determination coefficients (r) ≥ 0.9956, when the concentration of ethoxysulfuron was in the range 0.5–50 μg/L and that of the other three analytes was in the range 1.0–500 μg/L. The RSDwR for within-laboratory reproducibility was 5.7%. The validated method was successfully used to analyze real samples.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2018.01.017
      Issue No: Vol. 1537 (2018)
       
  • Magnetic mesoporous molecularly imprinted polymers based on surface
           precipitation polymerization for selective enrichment of triclosan and
           triclocarban
    • Authors: Xuemei Wang; Pengfei Huang; Xiaomin Ma; Xinzhen Du; Xiaoquan Lu
      Pages: 35 - 42
      Abstract: Publication date: 16 February 2018
      Source:Journal of Chromatography A, Volume 1537
      Author(s): Xuemei Wang, Pengfei Huang, Xiaomin Ma, Xinzhen Du, Xiaoquan Lu
      Novel magnetic mesoporous molecularly imprinted polymers (MMIPs) were prepared based on surface precipitation polymerization using Triclosan (TCS) as template and methacrylic acid as functional monomer. The synthesized MMIPs-TCS were applied to the adsorbent of magnetic solid-phase extraction (MSPE) coupled with HPLC for the enrichment and determination of TCS. The MMIPs-TCS were characterized by fourier-transform infrared spectrometry (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption transmission, and vibrating sample magnetometry. Under the optimum condition, the MMIPs-TCS-MSPE-HPLC method shows low limits of detection (LODs) (0.20–0.90 μg L−1) and limits of quantification detection (LOQs) (0.66–2.97 μg L−1), wide linear ranges from 10.0 to 1000 μg L−1 for each compound with exception of 2,4,6-TCP from 20.0 to 1000 μg L−1, and acceptable reproducibility (relative standard deviation, RSD <6.6% for intra-day, RSD <8.1% for inter-day). The satisfactory recoveries were in the range of 89.5%–108.4% with good RSDs less than 8.0% at the three spiked levels of 20, 50 and 80 μg L−1. Moreover, the adsorption experiments show the MMIPs-TCS possess rapid binding affinity, excellent magnetic response, specific selectivity and high adsorption capacity toward TCS with a maximum adsorption capacity of 1955.8 μg g−1.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2018.01.023
      Issue No: Vol. 1537 (2018)
       
  • Likelihood of total resolution in selective comprehensive two-dimensional
           liquid chromatography with parallel processing: Simulation and theory
    • Authors: Joe M. Davis; Dwight R. Stoll
      Pages: 43 - 57
      Abstract: Publication date: 16 February 2018
      Source:Journal of Chromatography A, Volume 1537
      Author(s): Joe M. Davis, Dwight R. Stoll
      The probability Pr ( sLC × LC ) that all peaks are separated by a resolution of 1.5 or more in selective comprehensive two-dimensional liquid chromatography (sLC × LC) is computed for simple model systems of 5 to 60 peaks and first-dimension (1 D) gradient times of 100 to 2000 s. The computations include mimics of a commercial instrument, whose fixed second-dimension (2 D) gradient time and use of one cycle time for initialization reduces Pr ( sLC × LC ) relative to an earlier report. For serial sLC × LC, in which a single device collects and transfers 1 D multiplets to the second dimension, Pr ( sLC × LC ) under practical conditions is predicted to be only slightly larger than the probability of total resolution in LC × LC for separations of the same duration in each case. To increase Pr ( sLC × LC ) , two model systems are proposed based on parallel processing, in which one device collects multiplets from the first separation while a second device simultaneously transfers fractions from previously collected multiplets to the second dimension for further separation. A sum of probabilities guideline is proposed by which optimal fixed 2 D gradient times, ranging from 9.5 to 12 s, are found for both serial and parallel models. The increases of Pr ( sLC × LC ) based on parallel processing are modest; the largest is only 0.062 for one system and 0.106 for the other, relative to the serial model. A theory is derived that rationalizes the modesty of the increase, which was unexpected. It shows that Pr ( sLC × LC ) equals the probability of total resolution in the first dimension, plus the product of the probability that all 1 D multiplets are transferred to the second dimension and the probability that all multiplets are separated in the second dimension. The theory shows that, although parallel processing is better than serial processing for multiplet transfer, the ability to leverage this gain is offset by the limited probability that all multiplets are then actually separated in the second dimension, which is only about 0.55 for conditions where the change from serial to parallel processing is most beneficial. With these findings in hand, two scenarios are examined for future consideration: one in which the 2 D peak capacity is doubled, and another in which multiplets are always transferred to the second dimension. The latter shows considerable promise for increasing Pr ( sLC × LC ) substantially beyond its counterpart in LC × LC. For example, a 50% probability of separating all peaks in a 15-component mixture can be reached in 1150 s using LC × LC. The same probability can be reached in the same time for a sample with nearly twice as many components (27) in the case of sLC × LC, assuming transfer of all multiplets to the second dimension. These findings will be useful to those considering systematic approaches to developing 2D-LC methods for moderately complex mixtures, and to those interested in instrument development for 2D-LC.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.12.035
      Issue No: Vol. 1537 (2018)
       
  • Peptide retention prediction using hydrophilic interaction liquid
           chromatography coupled to mass spectrometry
    • Authors: Majors J. Badgett; Barry Boyes; Ron Orlando
      Pages: 58 - 65
      Abstract: Publication date: 16 February 2018
      Source:Journal of Chromatography A, Volume 1537
      Author(s): Majors J. Badgett, Barry Boyes, Ron Orlando
      A model that predicts retention for peptides using a HALO® penta-HILIC column and gradient elution was created. Coefficients for each amino acid were derived using linear regression analysis and these coefficients can be summed to predict the retention of peptides. This model has a high correlation between experimental and predicted retention times (0.946), which is on par with previous RP and HILIC models. External validation of the model was performed using a set of H. pylori samples on the same LC–MS system used to create the model, and the deviation from actual to predicted times was low. Apart from amino acid composition, length and location of amino acid residues on a peptide were examined and two site-specific corrections for hydrophobic residues at the N-terminus as well as hydrophobic residues one spot over from the N-terminus were created.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.12.055
      Issue No: Vol. 1537 (2018)
       
  • Scalability of pre-packed preparative chromatography columns with
           different diameters and lengths taking into account extra column effects
    • Authors: Susanne Schweiger; Alois Jungbauer
      Pages: 66 - 74
      Abstract: Publication date: 16 February 2018
      Source:Journal of Chromatography A, Volume 1537
      Author(s): Susanne Schweiger, Alois Jungbauer
      Small pre-packed columns are commonly used to estimate the optimum run parameters for pilot and production scale. The question arises if the experiments obtained with these columns are scalable, because there are substantial changes in extra column volume when going from a very small scale to a benchtop column. In this study we demonstrate the scalability of pre-packed disposable and non-disposable columns of volumes in the range of 0.2–20 ml packed with various media using superficial velocities in the range of 30–500 cm/h. We found that the relative contribution of extra column band broadening to total band broadening was not only high for columns with small diameters, but also for columns with a larger volume due to their wider diameter. The extra column band broadening can be more than 50% for columns with volumes larger than 10 ml. An increase in column diameter leads to high additional extra column band broadening in the filter, frits, and adapters of the columns. We found a linear relationship between intra column band broadening and column length, which increased stepwise with increases in column diameter. This effect was also corroborated by CFD simulation. The intra column band broadening was the same for columns packed with different media. An empirical engineering equation and the data gained from the extra column effects allowed us to predict the intra, extra, and total column band broadening just from column length, diameter, and flow rate.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2018.01.022
      Issue No: Vol. 1537 (2018)
       
  • A microfluidic distributor combining minimal volume, minimal dispersion
           and minimal sensitivity to clogging
    • Authors: Sander Jespers; Sander Deridder; Gert Desmet
      Pages: 75 - 82
      Abstract: Publication date: 16 February 2018
      Source:Journal of Chromatography A, Volume 1537
      Author(s): Sander Jespers, Sander Deridder, Gert Desmet
      A new type of microfluidic flow distributor (referred to as the mixed mode or MM-distributor) is proposed. Its performance characteristics are determined using computational fluid dynamics (CFD), both in the absence and the presence of clogging, which is an important problem in microfluidic systems. A comparison is made with two existing, well-performing distributor types: the bifurcating (BF) distributor and an optimized diverging distributor, the so-called radially interconnected (RI) distributor. It was found that, in the absence of clogging, the MM-distributor produces only a little more dispersion than the bifurcating (BF) distributor, but much less than the radially interconnected (RI) distributor. The dispersion in an MM-distributor also follows a similar dependency on its width (power ≅ 2) as the BF-distributor. The dispersion in the RI-distributor on the other hand displays a very disadvantageous 4th-order dependency on its width, prohibiting its use to distribute the flow across wide beds (order of millimeters or centimeters). These observations hold independently of the flow rate. With increasing degree of clogging, the MM-distributor rapidly becomes advantageous over the BF-distributor, owing to the fluid contact zones that are provided after each bifurcation step. This means that overall, and when the occurrence of clogging cannot be excluded, the MM-type distributor seems to offer the best possible compromise between the ability to cope with local clogging events and the dispersion in the absence of clogging.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2018.01.029
      Issue No: Vol. 1537 (2018)
       
  • Simultaneous quantification of epoxy and hydroxy fatty acids as oxidation
           products of triacylglycerols in edible oils
    • Authors: Wei Xia; Suzanne M. Budge
      Pages: 83 - 90
      Abstract: Publication date: 16 February 2018
      Source:Journal of Chromatography A, Volume 1537
      Author(s): Wei Xia, Suzanne M. Budge
      Epoxy and hydroxy fatty acids are important intermediates during lipid oxidation; quantification of both structures may help evaluate the extent of competition among various lipid oxidation pathways. This article describes a method to simultaneously determine saturated- and unsaturated- epoxy and hydroxy fatty acids derived from oxidation of vegetable oils. The experimental procedures employed transesterification with sodium methoxide, separation of epoxy and hydroxy fatty acid methyl esters (FAME) using solid-phase extraction (SPE), and trimethylsilyl (TMS) derivatization of hydroxy groups. GC–MS was used to identify the epoxy and hydroxy FAME in two different SPE fractions, while GC-flame ionization detection (GC-FID) was used to determine their quantities. Epoxy-octadecanoate/octadecenoate and hydroxy-octadecanoate/octadecenoate/octadecadienoate were determined as lipid oxidation products generated from oxidation of sunflower and canola oils. An isomer of methyl 13-hydroxyoctadeca-9,11-dienoate (13-HODE) TMS ether co-eluted with methyl 15-hydroxyoctadeca-9,12-dienoate TMS ether, which was only present in canola oil; thus, GC–MS-selected ion monitoring (GC–MS–SIM) was used to determine the concentration of 13-HODE. The proposed method has been successfully applied to monitor epoxy and hydroxy fatty acids in sunflower oil and canola oil oxidized at 40 °C.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.12.066
      Issue No: Vol. 1537 (2018)
       
  • Facile gas chromatography–tandem mass spectrometry stable isotope
           dilution method for the quantification of sesquiterpenes in grape
    • Authors: Nina Duhamel; Davide Slaghenaufi; Lisa I. Pilkington; Mandy Herbst-Johnstone; Roberto Larcher; David Barker; Bruno Fedrizzi
      Pages: 91 - 98
      Abstract: Publication date: 16 February 2018
      Source:Journal of Chromatography A, Volume 1537
      Author(s): Nina Duhamel, Davide Slaghenaufi, Lisa I. Pilkington, Mandy Herbst-Johnstone, Roberto Larcher, David Barker, Bruno Fedrizzi
      Sesquiterpenes are a widespread class of compounds of increasing interest found in grapes and wines, amongst many other natural sources. Due to a lack of standards and the complexity of the mass spectra fragmentation, accurate quantification of these low concentration compounds had not previously been accomplished. The current paper presents a new method for the concurrent quantification of several sesquiterpenes. The multivariate method optimisation is presented. Synthesised isotopic standards were utilised in conjunction with solid phase microextraction (SPME) and gas chromatography-tandem mass spectrometry (GC–MS/MS) to perform a standard isotope dilution assay (SIDA). The method was successfully applied to several grape must samples of four different cultivar. To the best of our knowledge this was the first time some of these sesquiterpenes were quantified in grape.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.12.065
      Issue No: Vol. 1537 (2018)
       
  • Enhancing the chemical selectivity in discovery-based analysis with tandem
           ionization time-of-flight mass spectrometry detection for comprehensive
           two-dimensional gas chromatography
    • Authors: Chris E. Freye; Nicholas R. Moore; Robert E. Synovec
      Pages: 99 - 108
      Abstract: Publication date: 16 February 2018
      Source:Journal of Chromatography A, Volume 1537
      Author(s): Chris E. Freye, Nicholas R. Moore, Robert E. Synovec
      The complementary information provided by tandem ionization time-of-flight mass spectrometry (TI-TOFMS) is investigated for comparative discovery-based analysis, when coupled with comprehensive two-dimensional gas chromatography (GC × GC). The TI conditions implemented were a hard ionization energy (70 eV) concurrently collected with a soft ionization energy (14 eV). Tile-based Fisher ratio (F-ratio) analysis is used to analyze diesel fuel spiked with twelve analytes at a nominal concentration of 50 ppm. F-ratio analysis is a supervised discovery-based technique that compares two different sample classes, in this case spiked and unspiked diesel, to reduce the complex GC × GC-TI-TOFMS data into a hit list of class distinguishing analyte features. Hit lists of the 70 eV and 14 eV data sets, and the single hit list produced when the two data sets are fused together, are all investigated. For the 70 eV hit list, eleven of the twelve analytes were found in the top thirteen hits. For the 14 eV hit list, nine of the twelve analytes were found in the top nine hits, with the other three analytes either not found or well down the hit list. As expected, the F-ratios per m/z used to calculate each average F-ratio per hit were generally smaller fragment ions for the 70 eV data set, while the larger fragment ions were emphasized in the 14 eV data set, supporting the notion that complementary information was provided. The discovery rate was improved when F-ratio analysis was performed on the fused data sets resulted in eleven of the twelve analytes being at the top of the single hit list. Using PARAFAC, analytes that were “discovered” were deconvoluted in order to obtain their identification via match values (MV). Location of the analytes and the “F-ratio spectra” obtained from F-ratio analysis were used to guide the deconvolution. Eight of the twelve analytes where successfully deconvoluted and identified using the in-house library for the 70 eV data set. PARAFAC deconvolution of the two separate data sets provided increased confidence in identification of “discovered” analytes. Herein, we explore the limit of analyte discovery and limit of analyte identification, and demonstrate a general workflow for the investigation of key chemical features in complex samples.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2018.01.008
      Issue No: Vol. 1537 (2018)
       
  • Early stages in the history of gas chromatography
    • Authors: Ivan G. Kolomnikov; Alexander M. Efremov; Tatyana I. Tikhomirova; Nadezhda M. Sorokina; Yury A. Zolotov
      Pages: 109 - 117
      Abstract: Publication date: 16 February 2018
      Source:Journal of Chromatography A, Volume 1537
      Author(s): Ivan G. Kolomnikov, Alexander M. Efremov, Tatyana I. Tikhomirova, Nadezhda M. Sorokina, Yury A. Zolotov
      The creation of gas chromatography is traditionally associated with the names of Nobel Prize winner Archer Martin and his colleagues Richard Synge and Anthony James. However, sometimes references to their predecessors can be found. An investigation conducted by the authors of this article not only confirmed the reliability of these references; but in fact led to the conclusion that by 1952, which is commonly believed to be the year when gas chromatography was born, many research papers had already been devoted to this method, mainly, in its gas-solid version. These papers are considered in this article.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2018.01.006
      Issue No: Vol. 1537 (2018)
       
  • Profiling of modified nucleosides from ribonucleic acid digestion by
           supercritical fluid chromatography coupled to high resolution mass
           spectrometry
    • Authors: Laurent Laboureur; Vincent Guérineau; Sylvie Auxilien; Satoko Yoshizawa; David Touboul
      Pages: 118 - 127
      Abstract: Publication date: 16 February 2018
      Source:Journal of Chromatography A, Volume 1537
      Author(s): Laurent Laboureur, Vincent Guérineau, Sylvie Auxilien, Satoko Yoshizawa, David Touboul
      A method based on supercritical fluid chromatography coupled to high resolution mass spectrometry for the profiling of canonical and modified nucleosides was optimized, and compared to classical reverse-phase liquid chromatography in terms of separation, number of detected modified nucleosides and sensitivity. Limits of detection and quantification were measured using statistical method and quantifications of twelve nucleosides of a tRNA digest from E. coli are in good agreement with previously reported data. Results highlight the complementarity of both separation techniques to cover the largest view of nucleoside modifications for forthcoming epigenetic studies.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.12.020
      Issue No: Vol. 1537 (2018)
       
  • Screening of break point cluster region Abelson tyrosine kinase inhibitors
           by capillary electrophoresis
    • Authors: Mei Xu; Mengmeng Zheng; Guizhen Liu; Meng Zhang; Jingwu Kang
      Pages: 128 - 134
      Abstract: Publication date: 16 February 2018
      Source:Journal of Chromatography A, Volume 1537
      Author(s): Mei Xu, Mengmeng Zheng, Guizhen Liu, Meng Zhang, Jingwu Kang
      In the present study, a capillary electrophoresis (CE) method was developed for screening of inhibitors against the break point cluster region Abelson tyrosine kinase (BCR-ABL). The screening method was established by using 5-carboxyfluorescein labeled peptide substrate of BCR-ABL (F-ABLS), a known BCR-ABL tyrosine kinase inhibitor dasatinib, as well as a small chemical library consisting of 37 natural products. Thus, the inhibition of BCL-ABL kinase by small inhibitors was assayed by a CE system equipped with the laser induced fluorescence detector. The yield of phosphorylated product could be precisely measured through the separation by CE. The method is competent for enzymatic inhibition assay as well as the measurement of the inhibition kinetics. For screening BCR-ABL tyrosine kinase inhibitors, the hits were readily identified once the peak area of the phosphorylated products was reduced in comparison with the negative control. By taking the advantage of the screening method, luteolin and epicatechin gallate were discovered as the new BCR-ABL inhibitors.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2018.01.019
      Issue No: Vol. 1537 (2018)
       
  • Use of counter-current chromatography as a selective extractor for the
           diterpenequinone 7α-hydroxyroyleanone from Tetradenia riparia
    • Authors: Jonatas Vicente Milato; Raphael Salles Ferreira Silva; Fabiana de Souza Figueiredo; Debora de Almeida Azevedo; Carlos Alexandre Bulchi Ribeiro; Gilda Guimarães Leitão
      Pages: 135 - 140
      Abstract: Publication date: 16 February 2018
      Source:Journal of Chromatography A, Volume 1537
      Author(s): Jonatas Vicente Milato, Raphael Salles Ferreira Silva, Fabiana de Souza Figueiredo, Debora de Almeida Azevedo, Carlos Alexandre Bulchi Ribeiro, Gilda Guimarães Leitão
      A solvent system was developed for selective isolation by high-speed counter-current chromatography (HSCCC) of the benzoquinone 7α-hydroxyroileanone, 1, a bioactive diterpene from a dichloromethane extract of Tetradenia riparia leaves. Several solvent systems were initially studied, including hexane-ethyl acetate-methanol-water in several ratios, hexane-acetone-methanol-water, hexane-ethanol-water and hexane-acetonitrile-methanol, which gave recovery rates for the target compound between 13.4 and 35.9%. The new solvent system hexane-5% aqueous Na2CO3 (1:1) was developed based on the chemical ionization reaction of the benzoquinone hydroxyl group in the basic pH of the carbonate solution, prompted by the extraction procedure used for the extraction of lapachol (a natural naphtoquinone) from a Tabebuia species wood. By using the HSCCC chromatograph as a liquid–liquid extractor with the above mentioned solvent system the recovery rate of 1 increased to 81.8%, affording the quinone with 97% purity.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2018.01.020
      Issue No: Vol. 1537 (2018)
       
  • Profiling of polyunsaturated fatty acids in human serum using off-line and
           on-line solid phase extraction-nano-liquid
           chromatography-quadrupole-time-of-flight mass spectrometry
    • Authors: Wan-yi Gu; Mei-xian Liu; Bao-qing Sun; Ming-quan Guo; Jian-lin Wu; Na Li
      Pages: 141 - 146
      Abstract: Publication date: 16 February 2018
      Source:Journal of Chromatography A, Volume 1537
      Author(s): Wan-yi Gu, Mei-xian Liu, Bao-qing Sun, Ming-quan Guo, Jian-lin Wu, Na Li
      Polyunsaturated fatty acids (PUFAs) play a pivotal role in the biological effects, and are the potential biomarkers for some diseases. However, the structural diversity and similarity, the low concentration, and the interference of high abundant endogenous components challenge the PUFAs profiling. Herein, a novel analytical approach, off-line and on-line solid phase extraction-nano-liquid chromatography-quadrupole-time-of-flight mass spectrometry (off-line and on-line SPE-nano-LC-Q-TOF-MS), was established to monitor the PUFAs. The combination of off-line and on-line SPE removed most of impurities, and the recoveries ranged from 80.1% to 93.0% and the matrix effects were from 85.1% to 92.8%. Using this method, 51 PUFAs could be separated well and quantified with the limits of quantification between 0.006 and 2.2 pg. Finally, this developed method was applied successfully to simultaneously qualify and quantify the potential biomarkers in the allergic patients. 21 PUFAs including LTB4, 5S-, 11S-, 15S-HETE and 15S-HEPE showed significant differences. Our study indicated that the established method has the potential to sensitively and accurately determine the PUFAs in biological samples.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2018.01.015
      Issue No: Vol. 1537 (2018)
       
  • Comprehensive two-dimensional gas chromatography: A perspective on
           processes of modulation
    • Authors: Peter Q. Tranchida
      Pages: 2 - 5
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): Peter Q. Tranchida
      The first comprehensive two-dimensional gas chromatography (GC×GC) experiment was reported about 25 years ago [J. Chromatogr. Sci. 29 (1991) 227–231]; the GC×GC process was made possible by the development of a transfer device, defined as modulator. The process of modulation enables the isolation of effluent segments from the first column, and their re-injection onto the second column, in a continuous and sequential manner throughout the analysis. Over the years, many types of modulation systems have been introduced, each with specific advantages and disadvantages. Cryogenic systems are, at present, the most popular devices and represent the most effective form of modulation. The present contribution is focused on possible future scenarios, with respect to modulation, and as a consequence related to comprehensive GC, in general. The development of new forms of modulation may open the road to a more widespread use of GC×GC technologies.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.04.039
      Issue No: Vol. 1536 (2018)
       
  • The multi-mode modulator: A versatile fluidic device for two-dimensional
           gas chromatography
    • Authors: John V. Seeley; Nicolaas E. Schimmel; Stacy K. Seeley
      Pages: 6 - 15
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): John V. Seeley, Nicolaas E. Schimmel, Stacy K. Seeley
      A fluidic device called the multi-mode modulator (MMM) has been developed for use as a comprehensive two-dimensional gas chromatography (GC x GC) modulator. The MMM can be employed in a wide range of capacities including as a traditional heart-cutting device, a low duty cycle GC x GC modulator, and a full transfer GC x GC modulator. The MMM is capable of producing narrow component pulses (widths <50ms) while operating at flows compatible with high resolution chromatography. The sample path of modulated components is confined to the interior of a joining capillary. The joining capillary dimensions and the position of the columns within the joining capillary can be optimized for the selected modulation mode. Furthermore, the joining capillary can be replaced easily and inexpensively if it becomes fouled due to sample matrix components or column bleed. The principles of operation of the MMM are described and its efficacy is demonstrated as a heart-cutting device and as a GC x GC modulator.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.06.030
      Issue No: Vol. 1536 (2018)
       
  • Implications of phase ratio for maximizing peak capacity in comprehensive
           two-dimensional gas chromatography time-of-flight mass spectrometry
    • Authors: Brendon A. Parsons; David K. Pinkerton; Robert E. Synovec
      Pages: 16 - 26
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): Brendon A. Parsons, David K. Pinkerton, Robert E. Synovec
      The relationship between the phase ratio, β, of the primary (1D) and secondary (2D) separation dimensions of comprehensive two-dimensional (2D) gas chromatography (GC×GC) separations, and the implications of β on realization of maximal 2D peak capacity, n c,2D, are examined. A GC×GC chromatographic system with time-of-flight mass spectrometry, TOFMS, was otherwise held constant for the separation of a multi-component test mixture spanning a range of chemical functionalities, while only the β of the two analytical columns were changed, 1 β for 1D and 2 β for 2D. Six column sets were studied using common, commercially available β values. The β ratio, β R = 1 β/2 β, is defined as a quantitative metric to facilitate this study. It is demonstrated that β R plays a key role in maximizing n c,2D. Overall, β R substantially affected n c,2D by influencing retention factors on the 2D column, 2 k, and thereby changing the modulation period, P M, necessary for proper 2D column separations. The necessary changes to P M modify the modulation ratio, M R, which affects the 1D column peak widths and 1 nc due to the impact of undersampling. Through changes to 1 β, the range of 2 k can be controlled, with subsequent effects to both 2 n c and 1 n c. These effects were opposite in direction, such that improvements to 2 n c may result in declines in 1 n c. It is observed that due to the pseudo-isothermal nature of the 2D separation, there are diminishing returns to extending the 2 n c at the cost of 1 n c. In this particular study, column set 3 (1D: 20m length, 250μm i.d., 0.25μm film; 2D: 2m, 180μm i.d., 0.2μm film; β R =1.11) with a P M of 3s provided the highest theoretical n c,2D of ∼8200, though this was at a relatively low M R of ∼1.8. Column set 2 (1D: 20m length, 250μm i.d., 0.5μm film; 2D: 2m, 180μm i.d., 0.2μm film; β R =0.56) with a P M of 1.5s provided a high theoretical n c,2D of ∼5800, at a much higher M R of ∼3.7. Though column set 2 had a lesser total peak capacity than column set 3, its higher M R suggests that by improving the 1D column efficiency (i.e., narrowing the 1D column peak widths) to improve 1 n c, can result in an increased theoretical n c,2D.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.07.018
      Issue No: Vol. 1536 (2018)
       
  • Flow optimization in one-dimensional and comprehensive two-dimensional gas
           chromatography
    • Authors: Leonid M. Blumberg
      Pages: 27 - 38
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): Leonid M. Blumberg
      Theoretical considerations of optimal flow in a GC column under different conditions are outlined from a single perspective, and numerical recommendations are provided. The optimal flow rate in a temperature programmed column is about 30% lower than its isothermal counterpart in the same column with the same carrier gas. A simplified calculation of recommended optimal or near optimal flow rate in a single column under different conditions is summarized in a single equation. In GC × GC, the primary column operates under temperature-programmed conditions while each secondary run is essentially isothermal. As a result, their flow optimization requirements are different. The complementary IDs (internal diameters) corresponding to equal optimal flow rates in both GC × GC columns should relate as 2 d = 0.7 ·1 d. Typical complementary ID pairs are tabulated. If choosing the complementary IDs is not an option, several ways to reconcile the difference in their optimal flow rates are considered. The most typical cases of the column mismatch are identified and their boundary conditions are formulated. The effect of the flow reconciliation in these column pairs on the performance of GC × GC analysis is evaluated.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.08.040
      Issue No: Vol. 1536 (2018)
       
  • Second dimension column ensemble pressure tuning in comprehensive
           two-dimensional gas chromatography
    • Authors: Khan M. Sharif; Chadin Kulsing; Ademario I. da Silva Junior; Philip J. Marriott
      Pages: 39 - 49
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): Khan M. Sharif, Chadin Kulsing, Ademario I. da Silva Junior, Philip J. Marriott
      A pressure tunable (PT) coupled column ensemble has been implemented for the second dimension (2D) separation in comprehensive two dimensional gas chromatography (GC×PTGC). This process requires two columns to be connected by a pressure junction, as a replacement for a single narrow bore, short column in 2D. Various 2D1 and 2D2 columns may be selected to provide complementary selectivity (polarity) compared to the 1D column. The tunable residence time arising from differential pressure drop in each 2D column results in a tunable fractional contribution of each column in the 2D separation. A sample mixture comprising different chemical classes, including alkanes and alcohols, is used to identify the feasibility and extent of selectivity tuning possible in GC×PTGC. The column length is also varied due to the imposed challenge of wraparound in the PT coupled column system as pressures are adjusted in the 2D separation. Different experimental parameters, stationary phase materials and column lengths have been applied to investigate and understand the separation behaviour of the 2D PT coupled column GC×GC system. Results are discussed considering analyte retention time, peak width, linear velocity and the contribution of each 2D column. A specific and unexpected example of GC×GC separation was demonstrated where the peak positions of polar and apolar compounds could almost swap their 2D retention position by application of PT. Kerosene was analysed as an example of complex sample analysis by GC×PTGC system. This process is shown to be a practical approach for altering different stationary phase selectivities in a single 2D arrangement in GC×GC.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.10.060
      Issue No: Vol. 1536 (2018)
       
  • A four dimensional separation method based on continuous heart-cutting gas
           chromatography with ion mobility and high resolution mass spectrometry
    • Authors: Christian Lipok; Jörg Hippler; Oliver J. Schmitz
      Pages: 50 - 57
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): Christian Lipok, Jörg Hippler, Oliver J. Schmitz
      A two-dimensional GC (2D-GC) method was developed and coupled to an ion mobility-high resolution mass spectrometer, which enables the separation of complex samples in four dimensions (2D-GC, ion mobilility spectrometry and mass spectrometry). This approach works as a continuous multiheart-cutting GC-system (GC+GC), using a long modulation time of 20s, which allows the complete transfer of most of the first dimension peaks to the second dimension column without fractionation, in comparison to comprehensive two-dimensional gas chromatography (GCxGC). Hence, each compound delivers only one peak in the second dimension, which simplifies the data handling even when ion mobility spectrometry as a third and mass spectrometry as a fourth dimension are introduced. The analysis of a plant extract from Calendula officinales shows the separation power of this four dimensional separation method. The introduction of ion mobility spectrometry provides an additional separation dimension and allows to determine collision cross sections (CCS) of the analytes as a further physicochemical constant supporting the identification. A CCS database with more than 800 standard substances including drug-like compounds and pesticides was used for CCS data base search in this work.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.07.013
      Issue No: Vol. 1536 (2018)
       
  • Human odor and forensics. Optimization of a comprehensive two-dimensional
           gas chromatography method based on orthogonality: How not to choose
           between criteria
    • Authors: Vincent Cuzuel; Audrey Sizun; Guillaume Cognon; Isabelle Rivals; François Heulard; Didier Thiébaut; Jérôme Vial
      Pages: 58 - 66
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): Vincent Cuzuel, Audrey Sizun, Guillaume Cognon, Isabelle Rivals, François Heulard, Didier Thiébaut, Jérôme Vial
      The use of comprehensive two-dimensional gas chromatography coupled with mass spectrometry would be a real asset for the forensic profiling of human hand odor. This paper focuses on the optimization of a comprehensive gas chromatography method using a synthetic mixture of 80 compounds representative of human hand odor composition. In order to rank the candidate column sets, instead of using a unique criterion, we used a chemometric tool called desirability which is based on Derringer functions and enables to consider several criteria simultaneously and hence to get the best compromise. Nine criteria including six orthogonality criteria were used to evaluate the quality and the efficiency of the separation. The desirability analysis lead to a straightforward ranking and an accurate overview of the results in two situations, with an objective of routine analysis and without. In both cases, the DB-1MS×DB-1701 set was found to be best suited for the separation of the considered mixture, however with different gradients.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.08.060
      Issue No: Vol. 1536 (2018)
       
  • A retention index system for comprehensive two-dimensional gas
           chromatography using polyethylene glycols
    • Authors: Cathrin Veenaas; Peter Haglund
      Pages: 67 - 74
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): Cathrin Veenaas, Peter Haglund
      The characterization and identification of compounds in complex real-world samples is quite difficult and new concepts and workflows are highly desirable. Retention indices (RIs) are widely used in gas chromatography (GC) to support the identification of unknown compounds. Several attempts have been made to introduce a similar concept for the second dimension in comprehensive two-dimensional (2D) GC (GC × GC) but, an easily applicable and robust system remains elusive. In the present study, a new RI system for GC × GC was developed. Polyethylene glycols (PEGs) were used in combination with a simple linear regression, with n-alkanes as reference points for virtually unretained compounds and PEG homologs as reference compounds for second-dimension RIs (PEG- 2I). The n-alkanes were assigned a PEG- 2I of zero and the distance between consecutive PEG homologs from PEG-2 (diethylene glycol) and higher were assigned a PEG- 2I value of 10. We used ethylene glycol and PEG-2 through PEG-10 as reference compounds, thereby covering a PEG- 2I range from 20.0 for ethylene glycol, over 50.0 for diethylene glycol (PEG-2) to 130.0 for decaethylene glycol (PEG-10); additional PEGs can be added to cover a wider polarity range. The PEG- 2I system was initially evaluated using a 30 m × 0.25 mm non-polar (5% phenyl, 0.25 μm film thickness) first-dimension column and a 1.6 m × 0.18 mm polar (50% phenyl, 0.18 μm film thickness) second-dimension column. This system was validated for use with non-polar first-dimension columns and a semi-polar (50% phenyl) second-dimension column, and exhibited robustness to changes in the carrier gas flow velocity, oven temperature ramping rate, and secondary oven temperature offset. An average relative standard deviation of 2.7%, equal to a 95% confidence interval of 1.27 PEG- 2I units, was obtained for the PEG- 2I values of 72 environmental pollutants. Additionally, the system was found to be applicable over a wide range of boiling points (in the current case, from n-heptane to n-dotriacontane (C7–C32)) and can be used with various column dimensions. Changing the second-dimension column to either a narrower 0.1 mm column or a wider 0.25 mm column, yielded similar 95%-percentiles to that of the 0.18 mm column, differing by only 3.20 and 2.80 PEG- 2I units, respectively. Moreover, methods for improving the system were suggested.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.08.062
      Issue No: Vol. 1536 (2018)
       
  • Analysis of underivatised low volatility compounds by comprehensive
           two-dimensional gas chromatography with a short primary column
    • Authors: Fábio Junior Moreira Novaes; Chadin Kulsing; Humberto Ribeiro Bizzo; Francisco Radler de Aquino Neto; Claudia Moraes Rezende; Philip John Marriott
      Pages: 75 - 81
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): Fábio Junior Moreira Novaes, Chadin Kulsing, Humberto Ribeiro Bizzo, Francisco Radler de Aquino Neto, Claudia Moraes Rezende, Philip John Marriott
      Comprehensive two-dimensional gas chromatography (GC×GC) approaches with cryogenic modulation were developed for the qualitative analysis of selected low volatility compounds in raw coffee bean extracts, without derivatisation. The approaches employed short first (1D) and second (2D) dimension columns, specifically a 1D 65% phenyl methyl siloxane column (11m) and a 2D 5% phenyl methyl siloxane column (1m), which allowed elution of high molar mass compounds (e.g.>600Da). Solutes included hydrocarbons, fatty acids, diterpenes, tocopherols, sterols, diterpene esters, and di- and triacylglycerides. An oven temperature program up to 370°C was employed. The effects of experimental conditions were investigated, revealing that the GC×GC results strongly depended on the cryogenic trap T, and oven T program. An appropriate condition was selected and further applied for group type analysis of low volatility compounds in green Arabica coffee beans. Retention indices were compiled for 1D GC analysis and were similar for the composite column data in GC×GC. The elution of some compounds was confirmed by use of authentic standards. The approach allowed direct analysis of coffee extract in ethyl acetate solution, with improved analyte peak capacity (approximately 200 compounds were detected) without prior fractionation or pre-treatment of the sample. This avoided potential hydrolysis of high molar mass conjugate esters as well as degradation of thermally labile compounds such as the derivatives of the diterpenes cafestol and kahweol.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.08.069
      Issue No: Vol. 1536 (2018)
       
  • Optimizing loop-type cryogenic modulation in comprehensive two-dimensional
           gas chromatography using time-variable combination of the dual-stage jets
           for analysis of crude oil
    • Authors: Guilherme L. Alexandrino; Gustavo R. de Sousa; Francisco de A.M. Reis; Fabio Augusto
      Pages: 82 - 87
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): Guilherme L. Alexandrino, Gustavo R. de Sousa, Francisco de A.M. Reis, Fabio Augusto
      The enhanced chromatographic capability of the comprehensive two-dimensional gas chromatography (GC×GC) has already found several applications in analytical chemistry comprising complex samples. However, setting the appropriate chromatographic conditions that maximize sensitivity and separation efficiency in GC×GC may be more difficult than in conventional one-dimension gas chromatography, mainly due to the additional parameters strictly related to the modulation. Loop-type cryogenic modulators have been currently used for crude oil analysis using GC×GC, requiring sometimes a laborious try-and-error procedure to properly tune the dual-jets elapsed times on modulation. In this work, the advantages of choosing a time-variable combination of cold and hot jets pulses in a loop-type cryogenic modulator is presented when performing the fingerprinting analysis of crude oils using GC×GC-QMS, contrary to the conventional procedure based on a single combination for the dual-stage jets. A design of experiments approach is proposed to most effectively optimize the time-variable combination of the dual-jets elapsed times while modulating the wide hydrocarbons range along the GC×GC analysis. The most abundant classes of hydrocarbons contained in the maltenes fraction of a crude oil sample, such as paraffins, aromatics, steranes and hopanes were successfully resolved.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.10.054
      Issue No: Vol. 1536 (2018)
       
  • Improved coverage of naphthenic acid fraction compounds by comprehensive
           two-dimensional gas chromatography coupled with high resolution mass
           spectrometry
    • Authors: David T. Bowman; Karl J. Jobst; Xavier Ortiz; Eric J. Reiner; Lesley A. Warren; Brian E. McCarry; Greg F. Slater
      Pages: 88 - 95
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): David T. Bowman, Karl J. Jobst, Xavier Ortiz, Eric J. Reiner, Lesley A. Warren, Brian E. McCarry, Greg F. Slater
      This study reports the first application of comprehensive two-dimensional gas chromatography coupled to a high-resolution quadrupole time-of-flight mass spectrometer (GC×GC/HRQTOF-MS) for the characterization of naphthenic acid fraction compounds (NAFCs) from the Alberta Oil Sands. High resolution mass spectrometry (HRMS) significantly increased the coverage of NAFCs in the mixture and allowed the differentiation of NAFCs from several chemical classes. It was demonstrated that GC×GC, in combination with the high mass accuracy and precision of the HRQTOF-MS, could distinguish chemical species with the C3 vs SH4 mass split at a much lower resolving power than required with direct infusion experiments. Mass defect plots were useful for visualizing the complex datasets generated by GC×GC/HRQTOF-MS and led to the identification of 1105 chemical species with unique elemental compositions (<5ppm mass accuracy). Mass defect plots were shown to be a powerful screening tool and enabled the detection of extensive isomer series from the SO2 chemical class, some of which have not been previously reported in oil sands related samples. The GC×GC/HRQTOF-MS approach is expected to improve NAFC monitoring programs since the technique allows the qualitative analysis of individual NAFCs and provides unique fingerprints via isomer distributions which may assist in future fingerprinting studies.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.07.017
      Issue No: Vol. 1536 (2018)
       
  • Comprehensive two-dimensional gas chromatography-mass spectrometry of
           complex mixtures of anaerobic bacterial metabolites of petroleum
           hydrocarbons
    • Authors: C.M. Aitken; I.M. Head; D.M. Jones; S.J. Rowland; A.G. Scarlett; C.E. West
      Pages: 96 - 109
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): C.M. Aitken, I.M. Head, D.M. Jones, S.J. Rowland, A.G. Scarlett, C.E. West
      Anaerobic biotransformation of petroleum hydrocarbons is an important alteration mechanism, both subsurface in geological reservoirs, in aquifers and in anoxic deep sea environments. Here we report the resolution and identification, by comprehensive two-dimensional gas chromatography-mass spectrometry (GC×GC–MS), of complex mixtures of aromatic acid and diacid metabolites of the anaerobic biodegradation of many crude oil hydrocarbons. An extended range of metabolites, including alkylbenzyl, alkylindanyl, alkyltetralinyl, alkylnaphthyl succinic acids and alkyltetralin, alkylnaphthoic and phenanthrene carboxylic acids, is reported in samples from experiments conducted under sulfate-reducing conditions in a microcosm over two years. The range of metabolites identified shows that the fumarate addition mechanism applies to the alteration of hydrocarbons with up to C8 alkylation in monoaromatics and that functionalisation of up to three ring aromatic hydrocarbons with at least C1 alkylation occurs. The GC×GC–MS method might now be applied to the identification of complex mixtures of metabolites in samples from real environmental oil spills.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.06.027
      Issue No: Vol. 1536 (2018)
       
  • Chemotyping of new hop (Humulus lupulus L.) genotypes using comprehensive
           two-dimensional gas chromatography with quadrupole accurate mass
           time-of-flight mass spectrometry
    • Authors: DanDan Yan; Yong Foo Wong; Laura Tedone; Robert A. Shellie; Philip J. Marriott; Simon P. Whittock; Anthony Koutoulis
      Pages: 110 - 121
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): DanDan Yan, Yong Foo Wong, Laura Tedone, Robert A. Shellie, Philip J. Marriott, Simon P. Whittock, Anthony Koutoulis
      Comprehensive two-dimensional gas chromatography with quadrupole accurate mass time-of-flight mass spectrometry (GC×GC-Q-TOFMS) is employed to profile Humulus lupulus L. (hop) essential oils. Comparison of characterised essential oils allows discrimination among chemotypes. Experimental and commercial hop genotypes displayed distinguishable chemotypic patterns among the volatile secondary metabolites making up their essential oils. In total, 210–306 unique compounds were detected (depending on specific genotype), with 99 of these compounds either positively or tentatively identified. Identified volatile secondary metabolites were grouped into esters, monoterpene hydrocarbons, oxygenated monoterpenes, sesquiterpene hydrocarbons, oxygenated sesquiterpenes and ketones. Terpenoids were the dominant chemical families across all hop genotypes analysed, representing between 67% and 90% of the total ion count. The multidimensional chromatographic profiles of hop essential oils are extremely information-rich, making GC×GC-Q-TOFMS useful for fast screening of new hybrid hop genotypes, and therefore informing breeding strategies to derive new commercial hop cultivars for the development of distinctive and desirable beers.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.08.020
      Issue No: Vol. 1536 (2018)
       
  • Advanced fingerprinting of high-quality cocoa: Challenges in transferring
           methods from thermal to differential-flow modulated comprehensive two
           dimensional gas chromatography
    • Authors: Federico Magagna; Erica Liberto; Stephen E. Reichenbach; Qingping Tao; Andrea Carretta; Luigi Cobelli; Matthew Giardina; Carlo Bicchi; Chiara Cordero
      Pages: 122 - 136
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): Federico Magagna, Erica Liberto, Stephen E. Reichenbach, Qingping Tao, Andrea Carretta, Luigi Cobelli, Matthew Giardina, Carlo Bicchi, Chiara Cordero
      The possibility to transfer methods from thermal to differential-flow modulated comprehensive two-dimensional gas chromatographic (GC×GC) platforms opens interesting perspectives for routine analysis of complex samples. Flow modulated platforms avoid the use of cryogenics, thereby simplifying laboratory operations and analyst supervision during intensive analytical sessions. This study evaluates the feasibility of transferring a fingerprinting method capable of classifying and discriminating cocoa samples based on the volatiles fraction composition according to their origin and processing steps. Previously developed principles of GC×GC method translation are applied to an original fingerprinting method, developed for a loop-type thermal modulated GC×GC–MS system, to engineer a method for a reverse-injection differential flow modulated platform (GC×2GC–MS/FID) with a dual-parallel secondary column and dual detection. Effective method translation preserves analytes elution order, 1D resolution, and 2D pattern coherence. The experimental results confirm the feasibility of translating fingerprinting method conditions while preserving the informative power of 2D peak patterns for sample classification and discrimination. Correct translation enables effective transfer of metadata (e.g., compound names and MS fragmentation patterns) by automatic template transformation and matching from the original/reference method to its translated counterpart. Although the adoption of a narrow bore (i.e. 0.1mm dc ) column in the first-dimension enabled operation under close-to-optimal conditions with the differential-flow modulation platform, due to the dual-parallel columns in the second-dimension, it resulted in lower overall method sensitivity. Nevertheless, fingerprinting accuracy was preserved and most of the key-aroma compounds and technological markers were effectively mapped, thus limiting the loss of fingerprinting information.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.07.014
      Issue No: Vol. 1536 (2018)
       
  • Detailed qualitative analysis of honeybush tea (Cyclopia spp.) volatiles
           by comprehensive two-dimensional gas chromatography coupled to
           time-of-flight mass spectrometry and relation with sensory data
    • Authors: Gaalebalwe Ntlhokwe; Magdalena Muller; Elizabeth Joubert; Andreas G.J. Tredoux; André de Villiers
      Pages: 137 - 150
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): Gaalebalwe Ntlhokwe, Magdalena Muller, Elizabeth Joubert, Andreas G.J. Tredoux, André de Villiers
      The volatile composition of honeybush (Cyclopia) species was studied by comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOF-MS). Headspace-solid phase micro-extraction (HS-SPME) was used to extract the volatile compounds from tea infusions prepared from the three species C. genistoides, C. maculata and C. subternata. A total of 287 compounds were identified, 101 of which were confirmed using reference standards, while the remainder were tentatively identified using mass spectral and retention index (RI) data. The identification power of TOF-MS enabled the tentative identification of 147 compounds for the first time in honeybush tea. The majority of the compounds identified were common to all three Cyclopia species, although there were differences in their relative abundances, and some compounds were unique to each of the species. In C. genistoides, C. maculata and C. subternata 265, 257 and 238 compounds were identified, respectively. Noteworthy was the tentative identification of cinnamaldehyde in particular C. maculata samples, which points to the likely contribution of this compound to their distinct sensory profiles. This study emphasises the complexity of honeybush tea volatile composition and confirms the power of GC×GC combined with TOF-MS for the analysis of such complex samples.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.08.054
      Issue No: Vol. 1536 (2018)
       
  • Comprehensive two-dimensional gas chromatography coupled to high
           resolution time-of-flight mass spectrometry for screening of
           organohalogenated compounds in cat hair
    • Authors: Martin Brits; Peter Gorst-Allman; Egmont R. Rohwer; Jayne De Vos; Jacob de Boer; Jana M. Weiss
      Pages: 151 - 162
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): Martin Brits, Peter Gorst-Allman, Egmont R. Rohwer, Jayne De Vos, Jacob de Boer, Jana M. Weiss
      The coupling of comprehensive two-dimensional gas chromatography with high-resolution time-of-flight mass spectrometry offers the best separation efficiency combined with accurate mass measurements over a wide mass range. The tremendous power of this screening tool is illustrated by trace qualitative screening analysis of organohalogenated compounds (OHCs) in pet cat hair. Tentative identification was supported by mass spectral database searches and elemental formula prediction from the experimentally determined accurate mass data. This screening approach resulted in the first tentative identification of pentabromoethylbenzene, decabromodiphenyl ethane, hexabromocyclododecane, trisbromoneopentyl alcohol, tris(2-chloroethyl) phosphate and tris(2-chloroisopropyl)phosphate in the South African indoor environment. A total of seventy-two OHCs were identified in the samples and include known flame retardants, such as polybrominated diphenyl ethers, and legacy contaminants such as polychlorinated biphenyls and organochlorine, organophosphorous and pyrethroid pesticides. The results obtained from cat hair indicate that these pets are exposed to complex mixtures of OHCs and the detection of these compounds suggests that non-invasive cat hair samples can be used to model indoor exposure with reference to external deposition of OHCs present in the air and dust surrounding people. Toddlers share the same environment as pet cats and therefore also the same health risks.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.08.055
      Issue No: Vol. 1536 (2018)
       
  • Characterization of organic aromatic compounds in soils affected by an
           uncontrolled tire landfill fire through the use of comprehensive
           two-dimensional gas chromatography–time-of-flight mass spectrometry
    • Authors: J. Escobar-Arnanz; S. Mekni; G. Blanco; E. Eljarrat; D. Barceló; L. Ramos
      Pages: 163 - 175
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): J. Escobar-Arnanz, S. Mekni, G. Blanco, E. Eljarrat, D. Barceló, L. Ramos
      Discarded vehicle tires have become an increasing concern worldwide due to the enormous amount of wastes generated and the increasing evidence of health problems associated to their disposal and accidental combustion. Previous studies conducted involving either simulated or open uncontrolled tire fires have identified aromatics belonging to two main classes, volatile organic compounds and polycyclic aromatic compounds (PAHs), as the most relevant chemicals generated in these burning processes. As a consequence, and due to their recognized toxicity, most studies reported up to now have mainly focused on these two categories of compounds being information concerning the possible occurrence of other aromatic classes rather limited. In this study, the enhanced separation power and structural confirmation capabilities provided by comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry (GC×GC–ToF MS) has been used, for the first time, for the non-targeted analysis of soils impacted by a tire fire and an ash collected at the scene of the fire. In total, 118 volatile and semi-volatile aromatic compounds have been differentiated. Among them, 104 compounds have been either positively or tentatively identified. PAHs with 3–5 rings and their alkyl-derivatives were the most numerous and relevant classes in the investigated samples. A significant number of sulfur, oxygen- and nitrogen-containing PAHs were also detected in the samples. The application of a script function to the raw GC×GC–ToF MS data allowed the fast filtering and automatic recognition of compounds containing halogens in their structure. This part of the study evidenced that only a limited number of regulated persistent organic pollutants were present in the investigated samples. However, it also revealed the presence of emerging organophosphorous flame retardants, whose levels in tire fire impacted soils are reported for the first time.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.10.044
      Issue No: Vol. 1536 (2018)
       
  • Active modulation in neat carbon dioxide packed column comprehensive
           two-dimensional supercritical fluid chromatography
    • Authors: Orjen Petkovic; Pierre Guibal; Patrick Sassiat; Jérôme Vial; Didier Thiébaut
      Pages: 176 - 184
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): Orjen Petkovic, Pierre Guibal, Patrick Sassiat, Jérôme Vial, Didier Thiébaut
      After demonstrating in a first paper the feasibility of SFCxSFC without decompression of the mobile phase, a modified interface has been developed in order to perform active modulation between the two SFC dimensions. In this paper, it is shown that the new interface enabled independent control of modulation parameters in SFCxSFC and performed a band compression effect of solutes between the two SFC dimensions. The effectiveness of this new modulation process was studied using a Design of Experiments. The SFCxSFC prototype was applied to the analysis of a real oil sample to demonstrate the benefits of the active modulator; in comparison to our previous results obtained without active modulation, better separation was obtained with the new interface owing to the peak compression occurring in the modulator.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.08.063
      Issue No: Vol. 1536 (2018)
       
  • Implications of turbulent flow in connecting capillaries used in high
           performance liquid chromatography
    • Authors: John Halvorson; Abraham M. Lenhoff; Monika Dittmann; Dwight R. Stoll
      Pages: 185 - 194
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): John Halvorson, Abraham M. Lenhoff, Monika Dittmann, Dwight R. Stoll
      The ongoing movement in HPLC toward the use of small columns packed with small particles for high speed separations results in eluted peaks with very small volumetric variances. Avoiding degradation of separation performance under these conditions requires careful consideration of all sources of extra-column peak dispersion. Recent trends towards decreased diameters of connecting capillaries and increased flow rates for analytical-scale separations can result in Reynolds numbers that exceed 2000. This raises the possibility of a transition from laminar to turbulent flow, thereby resulting in a higher than expected pressure drop across the capillary at a given flow rate. In this study we collected pressure drop data as a function of flow rate under many conditions relevant to modern HPLC. The variables studied included capillary diameter (50–120μm) and length (100–550mm), acetonitrile/water composition (0–100%), and temperature (20–80°C). Most of the work involved stainless steel capillaries, but a subset of experiments involved fused silica. We then used the experimental data to train a model that enables prediction of pressure drops for all of the conditions studied. We find that a single global friction factor profile is sufficient to predict pressure drops as a function of flow rate that are in qualitative agreement with the experimental results. The quantitative accuracy of these predictions is generally quite good, with a mean prediction error of about 2% over the entire range of conditions studied. Predictions for some outlying capillaries are not as good, with errors as high as −40%. This variability is probably due mainly to capillary-to-capillary variability, especially in the wall roughness, which is difficult to characterize definitively. We believe the model described here will be very useful to practicing chromatographers for predicting the conditions under which turbulent flow might develop in their connecting capillaries, and the magnitude of the pressure drop increase over that expected if flow were exclusively laminar.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2016.12.084
      Issue No: Vol. 1536 (2018)
       
  • Comprehensive two dimensional liquid chromatography as analytical strategy
           for pharmaceutical analysis
    • Authors: Marion Iguiniz; Florent Rouvière; Estelle Corbel; Nicolas Roques; Sabine Heinisch
      Pages: 195 - 204
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): Marion Iguiniz, Florent Rouvière, Estelle Corbel, Nicolas Roques, Sabine Heinisch
      Comprehensive on-line two-dimensional liquid chromatography (LCxLC) is expected to generate impressive peak capacities, which makes it a method of choice for the analysis of complex samples such as pharmaceuticals. A comparative study of different sets of chromatographic conditions including stationary phase, pH additive and organic modifier was carried out with two real pharmaceutical samples in order to find out the best analytical conditions for implementation of one or several generic on-line LCxLC separations. Our choice was based on the evaluation of both degree of orthogonality and practical sample peak capacity under linear gradient conditions. The potential of 190 combinations of chromatographic systems was compared. A set of 3 RPLCxRPLC configurations was found to be very attractive for both samples and in good agreement with the findings of a previous study carried out with 17 model compounds, thereby supporting the idea of using generic LCxLC conditions in the pharmaceutical area. The three selected 2D-systems were implemented for the on-line RPLCxRPLC-UV/MS analysis of two pharmaceutical samples. It was shown, for each sample, that these 2D-systems were able to generate an effective peak capacity close to 1000 in less than 50min. For each sample, baseline separation was obtained for every known compound and furthermore a large number of unknown impurities could also be separated and identified. Finally, in the proposed conditions, the total number of compounds detected was significantly improved from one RPLC separation to one RPLCxRPLC separation. Only a small additional gain was observed by performing a second RPLCxRPLC separation or even a third one.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.08.070
      Issue No: Vol. 1536 (2018)
       
  • Profiling of Vitis vinifera L. canes (poly)phenolic compounds using
           comprehensive two-dimensional liquid chromatography
    • Authors: Lidia Montero; Vania Sáez; Dietrich von Baer; Alejandro Cifuentes; Miguel Herrero
      Pages: 205 - 215
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): Lidia Montero, Vania Sáez, Dietrich von Baer, Alejandro Cifuentes, Miguel Herrero
      Grapevine canes, a pruning-derived by-product, possess a great amount of bioactive (poly)phenolic compounds belonging to different chemical classes, thus, having a good potential for further valorization. However, in order to properly design valorization strategies, the precise chemical composition of this material has to be known. Up to now, this chemical characterization has been based on analysis of different groups of components individually, due to difficulties related to their huge chemical variability. In this work, a comprehensive two-dimensional liquid chromatography-based method (LC×LC) is developed to obtain the profiles of (poly)phenolic compounds present in grapevine canes from several varieties. Three different set-ups have been tested and compared; the combination of diol and C18 columns produced the best results, allowing the characterization of the (poly)phenolic profile in around 80min. This way, 81 different components were detected in the samples; most of them could be tentatively assigned using the information provided by the DAD and MS detectors employed. Indeed, it has been possible to detect in a single run components belonging to stilbenoids, procyanidins and prodelphinidins of varying degrees of polymerization, some of them not formerly described in this natural source. The method has shown extremely good separation capabilities, and is characterized by high effective peak capacity (842) and orthogonality (A0 =78%). The obtained results demonstrate that Vitis vinifera L. canes may retain a great potential to be used as an underexploited natural source of bioactive compounds, with potential applications in different fields.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.06.013
      Issue No: Vol. 1536 (2018)
       
  • Online comprehensive two-dimensional hydrophilic interaction
           chromatography×reversed-phase liquid chromatography coupled with hybrid
           linear ion trap Orbitrap mass spectrometry for the analysis of phenolic
           acids in Salvia miltiorrhiza
    • Authors: Ji-Liang Cao; Song-Song Wang; Hao Hu; Cheng-Wei He; Jian-Bo Wan; Huan-Xing Su; Yi-Tao Wang; Peng Li
      Pages: 216 - 227
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): Ji-Liang Cao, Song-Song Wang, Hao Hu, Cheng-Wei He, Jian-Bo Wan, Huan-Xing Su, Yi-Tao Wang, Peng Li
      In the present study, a system was developed for the analysis of phenolic acids in Salvia miltiorrhiza using online comprehensive two-dimensional hydrophilic interaction chromatography and reversed-phase liquid chromatography coupled to a DAD detector and hybrid linear ion trap-Orbitrap mass spectrometry (HILIC×RP-DAD-ESI/HRMS/MSn). The system was configured based on the combination of an XBridge Amide column (150mm×4.6mm, 3.5μm) and Accucore PFP column (50mm×4.6mm, 2.6μm) for the first and second dimensions, respectively. An additional LC pump was used to dilute the eluent from the first dimension to decrease its elution strength in the second dimension. A back-flush trap column was selected as an interface to make up for the loss of efficiency and resolution due to the online dilution. Under the optimized conditions, a total of 196 peaks of polar compounds were successfully separated and detected in Salvia miltiorrhiza using the developed online HILIC×RP system, which exhibited high orthogonality (73%). The online combination of HILIC and RP provides powerful separation capability for the analysis of polar compounds in samples with complex matrices.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.09.041
      Issue No: Vol. 1536 (2018)
       
  • Development of an improved sample preparation platform for acidic
           endogenous hormones in plant tissues using electromembrane extraction
    • Authors: Joon Hyuk Suh; Sang Beom Han; Yu Wang
      Pages: 1 - 8
      Abstract: Publication date: 2 February 2018
      Source:Journal of Chromatography A, Volume 1535
      Author(s): Joon Hyuk Suh, Sang Beom Han, Yu Wang
      Despite their importance in pivotal signaling pathways due to trace quantities and complex matrices, the analysis of plant hormones is a challenge. Here, to improve this issue, we present an electromembrane extraction technology combined with liquid chromatography–tandem mass spectrometry for determination of acidic plant hormones including jasmonic acid, abscisic acid, salicylic acid, benzoic acid, gibberellic acid and gibberellin A4 in plant tissues. Factors influencing extraction efficiency, such as voltage, extraction time and stirring rate were optimized using a design of experiments. Analytical performance was evaluated in terms of specificity, linearity, limit of quantification, precision, accuracy, recovery and repeatability. The results showed good linearity (r2  > 0.995), precision and acceptable accuracy. The limit of quantification ranged from 0.1 to 10 ng mL−1, and the recoveries were 34.6–50.3%. The developed method was applied in citrus leaf samples, showing better clean-up efficiency, as well as higher sensitivity compared to a previous method using liquid–liquid extraction. Organic solvent consumption was minimized during the process, making it an appealing method. More noteworthy, electromembrane extraction has been scarcely applied to plant tissues, and this is the first time that major plant hormones were extracted using this technology, with high sensitivity and selectivity. Taken together, this work gives not only a novel sample preparation platform using an electric field for plant hormones, but also a good example of extracting complex plant tissues in a simple and effective way.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.12.068
      Issue No: Vol. 1535 (2018)
       
  • Application of a magnetic graphene nanocomposite for organophosphorus
           pesticide extraction in environmental water samples
    • Authors: Peng Wang; Mai Luo; Donghui Liu; Jing Zhan; Xueke Liu; Fang Wang; Zhiqiang Zhou; Peng Wang
      Pages: 9 - 16
      Abstract: Publication date: 2 February 2018
      Source:Journal of Chromatography A, Volume 1535
      Author(s): Peng Wang, Mai Luo, Donghui Liu, Jing Zhan, Xueke Liu, Fang Wang, Zhiqiang Zhou, Peng Wang
      A novel magnetic nanocomposite was prepared and applied for the extraction of organophosphorus pesticide residue (malathion, chlorpyrifos, isocarbophos, fenamiphos, profenofos) in environmental water by magnetic solid phase extraction. The magnetic nanocomposite was synthesized by coating Fe3O4 with silicon dioxide and then bonding with graphene oxide under the catalytic action of hydrazine hydrate. A residue analysis method for the determination of organophosphorus pesticides in environmental water was established via magnetic solid phase extraction with the nanocomposite as the sorbent, followed by gas chromatography with flame photometric detection (GC-FPD). Various experimental parameters affect extraction efficiency and must be optimized, such as the sorbent amount, the type and volume of desorption solvent, desorption time, desorption step, salt concentration and pH. Under the optimum conditions, a linear response was achieved for malathion and chlorpyrifos in the concentration range of 0.05 mg L−1–5 mg L−1. Other organophosphorus pesticides were quantified in a concentration range of 0.1 mg L−1–5 mg L−1, and the coefficient of correlations were between 0.996 and 1 for this method. The method was used to determine organophosphorus pesticides in river water and groundwater. The average recoveries ranged from 90.2% to 102.9%, with low relative standard deviations (RSD), and the limits of detection (LOD) were between 0.016 mg L−1 to 0.033 mg L−1 at a signal to noise ratio of 3. The method was efficient for the residue analysis of organophosphorus pesticides in water with easy operation, high sensitivity, and good precision.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2018.01.003
      Issue No: Vol. 1535 (2018)
       
  • Carbon nanotube-based benzyl polymethacrylate composite monolith as a
           solid phase extraction adsorbent and a stationary phase material for
           simultaneous extraction and analysis of polycyclic aromatic hydrocarbon in
           water
    • Authors: Asma’a Al-Rifai; Ahmad Aqel; Lamya Al Wahibi; Zeid A. ALOthman; Ahmed-Yacine Badjah-Hadj-Ahmed
      Pages: 17 - 26
      Abstract: Publication date: 2 February 2018
      Source:Journal of Chromatography A, Volume 1535
      Author(s): Asma’a Al-Rifai, Ahmad Aqel, Lamya Al Wahibi, Zeid A. ALOthman, Ahmed-Yacine Badjah-Hadj-Ahmed
      A composite of multi-walled carbon nanotubes incorporated into a benzyl methacrylate-co-ethylene dimethacrylate porous monolith was prepared, characterized and used as solid phase adsorbent and as stationary phase for simultaneous extraction and separation of ten polycyclic aromatic hydrocarbons, followed by nano-liquid chromatography analysis. The extraction and chromatographic parameters were optimized with regard to the extraction efficiency and the quality of chromatographic analytes separation. Under the optimized conditions, all PAHs were separated in 13 min with suitable resolution values (Rs = 1.74–3.98). Addition of a small amount of carbon nanotubes (0.1% with respect to monomers) to the polymerization mixture increased the efficiency for the separation column to over 41,700 plates m−1 for chrysene at flow rate of 0.5 μL min−1. The method showed a wide linear range (1–500 μg L−1 with R2 more than 0.9938), acceptable extraction repeatability (RSDs < 6.4%, n = 3) and reproducibility (RSDs < 12.6%, five parallel-made solid phase extraction cartridges) and satisfactory detection limits (0.02–0.22 μg L−1). Finally, the proposed method was successfully applied to the detection of polycyclic aromatic hydrocarbons in environmental water samples. After a simple extraction procedure with preconcentration factor equal to 100, the average recovery values in ultra-pure, tap and sea water samples were found to be in the range 81.3–95.4% with %RSD less than 6.4. Again, the presence of carbon nanotubes (0.3% relatively to monomers) in native polymer enhanced the extraction performance for the solid phase adsorbent up to 78.4%. The application of the monoliths modified with CNTs in extraction and nano-scale liquid chromatography for analysis of environmental samples offered several advantages; it demonstrated an acceptable precision, low detection limits, good reproducibility, satisfying recoveries and wide dynamic linear ranges.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2018.01.011
      Issue No: Vol. 1535 (2018)
       
  • Utilization of large volume zwitterionic hydrophilic interaction liquid
           chromatography for the analysis of polar pharmaceuticals in aqueous
           environmental samples: Benefits and limitations
    • Authors: Lise Boulard; Georg Dierkes; Thomas Ternes
      Pages: 27 - 43
      Abstract: Publication date: 2 February 2018
      Source:Journal of Chromatography A, Volume 1535
      Author(s): Lise Boulard, Georg Dierkes, Thomas Ternes
      Benefits and limitations of HILIC were studied for the analysis of extreme polar organic contaminants in aqueous environmental matrices. A sensitive analytical method was developed and validated for the detection of 11 pharmaceuticals, 15 pharmaceutical metabolites and transformation products and the artificial sweetener acesulfame in aqueous environmental samples. The analytical method consisted of a simple and non-specific sample preparation based on freeze-drying followed by detection with large injection volume (70 μL) zwitterionic HILIC-ESI-MS/MS. Robustness studies showed a high sensitivity of the retention times and peak shapes to variations of the acetonitrile/water ratio of both the eluent and the diluent. Thus, a thorough sample and eluent preparation is required to obtain reproducible results. Extreme matrix effects of >200% were observed for emtricitabine and acyclovir, which could be traced to the co-elution of nitrate and chloride, respectively. These matrix effects and those of other analytes could be efficiently compensated by using deuterated, 13C and 15N-labeled internal standards. The developed method was able to detect the selected 27 analytes in treated wastewater, surface water and groundwater down to limit of quantification (LOQ) in the lower ng/L range. Appreciable concentrations were detected, ranging up to 110 μg/L (guanyl urea) in treated wastewater, up to 5.1 μg/L (oxipurinol) in surface water and up to 6.1 μg/L (acesulfame) in groundwater. In a German drinking water, only the X-ray contrast medium diatrizoate and the artificial sweetener acesulfame were quantified above LOQ with 0.19 μg/L and 0.35 μg/L, respectively.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.12.023
      Issue No: Vol. 1535 (2018)
       
  • On-tubing fluorescence measurements of the band broadening of contemporary
           injectors in ultra-high performance liquid chromatography
    • Authors: Ken Broeckhoven; Kim Vanderlinden; Davy Guillarme; Gert Desmet
      Pages: 44 - 54
      Abstract: Publication date: 2 February 2018
      Source:Journal of Chromatography A, Volume 1535
      Author(s): Ken Broeckhoven, Kim Vanderlinden, Davy Guillarme, Gert Desmet
      We report on a detailed study of the injection contribution to band broadening in contemporary UHPLC-instruments, using either flow-through needle or fixed loop injection (full loop). Using on-tubing fluorescence measurements at the outlet of the injector valve, very localized and undisturbed measurements were obtained. Varying both the flow rate and the injected volume allowed to split the injection variance (σV 2 ,inj) in a volumetric component (related to the amount injected) and a hydrodynamic component (related to the flow rate). For the flow-through needle injector and for the small injection volumes (<2 μL) typically used in UHPLC, it was found that the volumetric contribution (i.e. the part of σV 2 ,inj, that increases with increasing injection volume) is given by a value of σV 2 ,inj,vol = 0.8 to 1·Vinj 2 rather than by the value of 0.125 to 0.2·Vinj 2 that is normally assumed in literature. For the hydrodynamic contribution to σV 2 ,inj, (i..e, the part which remains present even for very small injection volumes), a clear increase in dispersion with flow rate is found, reaching a plateau around 0.8ml/min of 0.6 μL² or 1.2 μL² for the 75 μm and 120 μm needle seat capillaries respectively. The difference between both shows the clear advantage of using a low dispersion 75 μm injection needle seat capillary. For a loop-type injector operated in a full-loop mode, the increase in peak variance with the injection volume is much less pronounced, leading to a total injector variance given by σV 2 ,inj = 0.34 μL² + 0.12·Vinj 2 over the entire range of investigated injection volumes of 1.1 μL up to 4.5 μL when using 120 μm or narrower ID loops. This expression was nearly completely independent of the flow rate. For larger ID sample loops, a clear increase of peak variance with flow rate at fixed injection volume was observed (σV 2 ,inj increases with 20% for a 170 μm ID loop and with 70% for a 220 μm ID loop from 0.3 to 1 ml/min).

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2017.12.032
      Issue No: Vol. 1535 (2018)
       
  • FOREWORD
    • Authors: Lourdes Ramos; Peter Tranchida Peter Schoenmakers
      Abstract: Publication date: 9 February 2018
      Source:Journal of Chromatography A, Volume 1536
      Author(s): Lourdes Ramos, Peter Q. Tranchida, Peter Schoenmakers


      PubDate: 2018-02-05T02:07:10Z
       
  • Thermodynamics of acid-base dissociation of several cathinones and
           1‐phenylethylamine, studied by an accurate capillary electrophoresis
           method free from the Joule heating impact
    • Authors: Paweł Mateusz Nowak; Michał Woźniakiewicz; Mariusz Mitoraj; Filip Sagan; Paweł Kościelniak
      Abstract: Publication date: Available online 3 February 2018
      Source:Journal of Chromatography A
      Author(s): Paweł Mateusz Nowak, Michał Woźniakiewicz, Mariusz Mitoraj, Filip Sagan, Paweł Kościelniak
      Capillary electrophoresis is often used to the determination of the acid-base dissociation/deprotonation constant (pK a), and the more advanced thermodynamic quantities describing this process (ΔH°, -TΔS°). Remarkably, it is commonly overlooked that due to insufficient dissipation of Joule heating the accuracy of parameters determined using a standard approach may be questionable. In this work we show an effective method allowing to enhance reliability of these parameters, and to estimate the magnitude of errors. It relies on finding a relationship between electrophoretic mobility and actual temperature, and performing pK a determination with the corrected mobility values. It has been employed to accurately examine the thermodynamics of acid-base dissociation of several amine compounds − known for their strong dependency of pK a on temperature: six cathinones (2-methylmethcathinone, 3‐methylmethcathinone, 4-methylmethcathinone, α‐pyrrolidinovalerophenone, methylenedioxypyrovalerone, and ephedrone); and structurally similar 1‐phenylethylamine. The average pK a error caused by Joule heating noted at 25 °C was relatively small − 0.04-0.05 pH unit, however, a more significant inaccuracy was observed in the enthalpic and, in particular, entropic terms. An alternative correction method has also been proposed, simpler and faster, but not such effective in correcting ΔH°/-TΔS° terms. The corrected thermodynamic data have been interpreted with the aid of theoretical calculations, on a ground of the enthalpy-entropy relationships and the most probable structural effects accounting for them. Finally, we have demonstrated that the thermal dependencies of electrophoretic mobility, modelled during the correction procedure, may be directly used to find optimal temperature providing a maximal separation efficiency.

      PubDate: 2018-02-05T02:07:10Z
      DOI: 10.1016/j.chroma.2018.01.047
       
 
 
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