Time filter

Source Type

Krupcik J.,Institute of Chemical Technology | Gorovenko R.,Institute of Chemical Technology | Spanik I.,Institute of Chemical Technology | Sandra P.,Research Institute for Chromatography | Armstrong D.W.,University of Texas at Arlington
Journal of Chromatography A | Year: 2013

Flow-modulated comprehensive two-dimensional gas chromatography with simultaneous monitoring of the separation by flame ionization (GC×GC-FID) and quadrupole mass spectrometric (GC×GC-qMSD) detection was studied for the analysis of gasoline and kerosene samples. The acquisition frequency of the FID was 100Hz and of the qMSD 18Hz for the mass range m/z 40-300. The instrumental set-up is such that both one-dimensional (GC-FID and GC-qMSD) and two-dimensional separations using the same working conditions can be performed. Gasoline and kerosene samples were analyzed on the column combination HP-5MS (1D)+HP INNOWax (2D). Three modulated peaks were obtained for each hydrocarbon present above 0.1% with ca. 300ms peak width at the base using 6 s modulation times. Modulated peaks in GC×GC-FID were thus characterized by ca. 30 points while those in GC×GC-qMSD method by 6-8 points only. The FID speed is sufficient for reliable quantitative analysis, while the qMSD scan speed is perfectly appropriate for identification purposes. Moreover, in the GC×GC-qMSD method considerably improved quality of uncorrected spectra was obtained, arising from the enhanced separation over one-dimensional GC-MSD analysis. Spectral match qualities of up to 98% were found. © 2013 Elsevier B.V.

Zapadlo M.,Palacky University | Krupcik J.,Institute of Chemical Technology | Majek P.,Institute of Chemical Technology | Armstrong D.W.,University of Texas at Arlington | Sandra P.,Research Institute for Chromatography
Journal of Chromatography A | Year: 2010

The orthogonality of three columns coupled in two series was studied for the congener specific comprehensive two-dimensional GC separation of polychlorinated biphenyls (PCBs). A non-polar capillary column coated with poly(5%-phenyl-95%-methyl)siloxane was used as the first (1D) column in both series. A polar capillary column coated with 70% cyanopropyl-polysilphenylene-siloxane or a capillary column coated with the ionic liquid 1,12-di(tripropylphosphonium)dodecane bis(trifluoromethane-sulfonyl)imide were used as the second (2D) columns. Nine multi-congener standard PCB solutions containing subsets of all native 209 PCBs, a mixture of 209 PCBs as well as Aroclor 1242 and 1260 formulations were used to study the orthogonality of both column series. Retention times of the corresponding PCB congeners on 1D and 2D columns were used to construct retention time dependences (apex plots) for assessing orthogonality of both columns coupled in series. For a visual assessment of the peak density of PCBs congeners on a retention plane, 2D images were compared. The degree of orthogonality of both column series was, along the visual assessment of distribution of PCBs on the retention plane, evaluated also by Pearson's correlation coefficient, which was found by correlation of retention times tR,i,2D and tR,i,1D of corresponding PCB congeners on both column series. It was demonstrated that the apolar+ionic liquid column series is almost orthogonal both for the 2D separation of PCBs present in Aroclor 1242 and 1260 formulations as well as for the separation of all of 209 PCBs. All toxic, dioxin-like PCBs, with the exception of PCB 118 that overlaps with PCB 106, were resolved by the apolar/ionic liquid series while on the apolar/polar column series three toxic PCBs overlapped (105+127, 81+148 and 118+106). © 2010 Elsevier B.V.

Pereira A.S.,Research Institute for Chromatography | Giron A.J.,Ghent University | Admasu E.,Ghent University | Sandra P.,Research Institute for Chromatography | Sandra P.,Ghent University
Journal of Separation Science | Year: 2010

In hydrophilic interaction chromatography (HILIC), best results are obtained with high concentrations of acetonitrile. In the framework of green chromatography, different concentrations of carbon dioxide were added to the mobile phases acetonitrile-water and ethanol-water and the impact on retention and separation in HILIC using bare silica as stationary phase was explored. The features of HILIC using enhanced-fluidity mobile phases are illustrated with the analysis of the nucleobases and a mixture containing the nucleobases and cortisol, flurbiprofen, theophylline and caffeine. For both organic constituents, the elution window is widened in function of the carbon dioxide concentration and selectivity changes. At high concentrations of carbon dioxide in ethanol, separations were similar to those obtained with acetonitrile without carbon dioxide addition. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cifkova E.,University of Pardubice | Holcapek M.,University of Pardubice | Lisa M.,University of Pardubice | Ovcacikova M.,University of Pardubice | And 4 more authors.
Analytical Chemistry | Year: 2012

The identification and quantitation of a wide range of lipids in complex biological samples is an essential requirement for the lipidomic studies. High-performance liquid chromatography-mass spectrometry (HPLC/MS) has the highest potential to obtain detailed information on the whole lipidome, but the reliable quantitation of multiple lipid classes is still a challenging task. In this work, we describe a new method for the nontargeted quantitation of polar lipid classes separated by hydrophilic interaction liquid chromatography (HILIC) followed by positive-ion electrospray ionization mass spectrometry (ESI-MS) using a single internal lipid standard to which all class specific response factors (RFs) are related to. The developed method enables the nontargeted quantitation of lipid classes and molecules inside these classes in contrast to the conventional targeted quantitation, which is based on predefined selected reaction monitoring (SRM) transitions for selected lipids only. In the nontargeted quantitation method described here, concentrations of lipid classes are obtained by the peak integration in HILIC chromatograms multiplied by their RFs related to the single internal standard (i.e., sphingosyl PE, d17:1/12:0) used as common reference for all polar lipid classes. The accuracy, reproducibility and robustness of the method have been checked by various means: (1) the comparison with conventional lipidomic quantitation using SRM scans on a triple quadrupole (QqQ) mass analyzer, (2) 31P nuclear magnetic resonance (NMR) quantitation of the total lipid extract, (3) method robustness test using subsequent measurements by three different persons, (4) method transfer to different HPLC/MS systems using different chromatographic conditions, and (5) comparison with previously published results for identical samples, especially human reference plasma from the National Institute of Standards and Technology (NIST human plasma). Results on human plasma, egg yolk and porcine liver extracts are presented and discussed. © 2012 American Chemical Society.

Gritti F.,University of Tennessee at Knoxville | dos Santos Pereira A.,Research Institute for Chromatography | Sandra P.,Research Institute for Chromatography | Guiochon G.,University of Tennessee at Knoxville
Journal of Chromatography A | Year: 2010

The dependencies on the mobile phase flow velocity of the efficiency of a column packed with shell particles of neat porous silica (Halo) was measured under two different sets of experimental conditions. These conditions corresponded to the retention mechanisms of per aqueous liquid chromatography (PALC) at low acetonitrile concentrations and of hydrophilic interaction chromatography (HILIC) at high acetonitrile concentrations. The results are compared. Small amounts of a diluted solution of caffeine were injected in order to record the chromatograms under strictly linear conditions. These efficiencies were measured in both water-rich (PALC retention mechanism) and acetonitrile-rich (HILIC mechanism) mobile phases for the same retention factors, between 0.25 and 2.5. The mobile phases were mixtures of acetonitrile and water containing neither supporting salt nor buffer component. At low retention factors, the efficiency of caffeine is better in the PALC than in the HILIC mode. For k′ = 0.5, the minimum reduced height equivalent to a theoretical plate (HETP) is close to 2.5 in PALC while it exceeds 5 in HILIC. The converse is true for high retention factors. For k′ > 2.5, the HETP is lower in HILIC than in PALC, because the major contribution to band broadening and peak tailing in this latter mode originates from the heterogeneous thermodynamics of retention and eventually restricts column performance in PALC. Most interestingly, the reduced HETP measured in HILIC for caffeine never falls below 4. This suggests that the mass transfer of caffeine between the multilayer adsorbed phase (due to the interactions of the strong solvent and the silanol groups) and the acetonitrile-rich bulk eluent is slow. © 2009 Elsevier B.V. All rights reserved.

Discover hidden collaborations