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Selected papers from the latest issue:
Multiple automated headspace in-tube extraction for the accurate analysis of relevant wine aroma compounds and for the estimation of their relative liquid–gas transfer rates
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
Julián Zapata, Ricardo Lopez, Paula Herrero, Vicente Ferreira
An automated headspace in-tube extraction (ITEX) method combined with multiple headspace extraction (MHE) has been developed to provide simultaneously information about the accurate wine content in 20 relevant aroma compounds and about their relative transfer rates to the headspace and hence about the relative strength of their interactions with the matrix. In the method, 5μL (for alcohols, acetates and carbonyl alcohols) or 200μL (for ethyl esters) of wine sample were introduced in a 2mL vial, heated at 35°C and extracted with 32 (for alcohols, acetates and carbonyl alcohols) or 16 (for ethyl esters) 0.5mL pumping strokes in four consecutive extraction and analysis cycles. The application of the classical theory of Multiple Extractions makes it possible to obtain a highly reliable estimate of the total amount of volatile compound present in the sample and a second parameter, β, which is simply the proportion of volatile not transferred to the trap in one extraction cycle, but that seems to be a reliable indicator of the actual volatility of the compound in that particular wine. A study with 20 wines of different types and 1 synthetic sample has revealed the existence of significant differences in the relative volatility of 15 out of 20 odorants. Differences are particularly intense for acetaldehyde and other carbonyls, but are also notable for alcohols and long chain fatty acid ethyl esters. It is expected that these differences, linked likely to sulphur dioxide and some unknown specific compositional aspects of the wine matrix, can be responsible for relevant sensory changes, and may even be the cause explaining why the same aroma composition can produce different aroma perceptions in two different wines.
Source:Journal of Chromatography A, Volume 1266
Julián Zapata, Ricardo Lopez, Paula Herrero, Vicente Ferreira
An automated headspace in-tube extraction (ITEX) method combined with multiple headspace extraction (MHE) has been developed to provide simultaneously information about the accurate wine content in 20 relevant aroma compounds and about their relative transfer rates to the headspace and hence about the relative strength of their interactions with the matrix. In the method, 5μL (for alcohols, acetates and carbonyl alcohols) or 200μL (for ethyl esters) of wine sample were introduced in a 2mL vial, heated at 35°C and extracted with 32 (for alcohols, acetates and carbonyl alcohols) or 16 (for ethyl esters) 0.5mL pumping strokes in four consecutive extraction and analysis cycles. The application of the classical theory of Multiple Extractions makes it possible to obtain a highly reliable estimate of the total amount of volatile compound present in the sample and a second parameter, β, which is simply the proportion of volatile not transferred to the trap in one extraction cycle, but that seems to be a reliable indicator of the actual volatility of the compound in that particular wine. A study with 20 wines of different types and 1 synthetic sample has revealed the existence of significant differences in the relative volatility of 15 out of 20 odorants. Differences are particularly intense for acetaldehyde and other carbonyls, but are also notable for alcohols and long chain fatty acid ethyl esters. It is expected that these differences, linked likely to sulphur dioxide and some unknown specific compositional aspects of the wine matrix, can be responsible for relevant sensory changes, and may even be the cause explaining why the same aroma composition can produce different aroma perceptions in two different wines.
Highlights
► We develop a multiple headspace in-tube extraction method to analyse wine volatiles. ► We validate this method to quantify 20 wine volatiles and we apply it to 21 wines. ► With the method we measure the relative liquid–gas transfer rates of the analytes. ► The method reveals differences in volatily for analytes in different wines.The mass transfer dynamics of hollow fiber liquid-phase microextraction and its application for rapid analysis of biological samples
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
Shufen Cui, Gangfeng Ouyang, Guijiao Duan, Jinxing Hou, Tiangang Luan, Xu Zhang
Hollow fiber liquid-phase microextraction (HF-LPME) has been demonstrated to potentially become a mainstream sample preparation technique for complex samples. Nevertheless, the need for a relatively long extraction time is considered to be the major disadvantage of this method. Lengthy extractions may cause the loss of the extraction phase and may change the contents of biological samples via the action of enzymes. Therefore, control calibrations for particular biological systems must be made. In this study, a theoretical model of the mass transfer dynamics of two-phase HF-LPME was proposed, and the kinetic calibration (KC) of this method for plasma and urine samples was validated. The theoretical results were validated by examining the kinetics of the extraction and back-extraction processes of HF-LPME. The KC-HF-LPME method was successfully used to correct for matrix effects in plasma and urine samples during flunitrazepam analysis. The free amount of flunitrazepam was extracted from plasma for 10min and analyzed by gas chromatography/mass spectrometry. The amount of pre-added standard and the standard remaining in the extraction phase after extraction were used for the quantification of flunitrazepam in plasma and urine samples. The new method not only significantly shortens the extraction time but also provides a new opportunity to determine the free concentration of analyte in biological systems.
Source:Journal of Chromatography A, Volume 1266
Shufen Cui, Gangfeng Ouyang, Guijiao Duan, Jinxing Hou, Tiangang Luan, Xu Zhang
Hollow fiber liquid-phase microextraction (HF-LPME) has been demonstrated to potentially become a mainstream sample preparation technique for complex samples. Nevertheless, the need for a relatively long extraction time is considered to be the major disadvantage of this method. Lengthy extractions may cause the loss of the extraction phase and may change the contents of biological samples via the action of enzymes. Therefore, control calibrations for particular biological systems must be made. In this study, a theoretical model of the mass transfer dynamics of two-phase HF-LPME was proposed, and the kinetic calibration (KC) of this method for plasma and urine samples was validated. The theoretical results were validated by examining the kinetics of the extraction and back-extraction processes of HF-LPME. The KC-HF-LPME method was successfully used to correct for matrix effects in plasma and urine samples during flunitrazepam analysis. The free amount of flunitrazepam was extracted from plasma for 10min and analyzed by gas chromatography/mass spectrometry. The amount of pre-added standard and the standard remaining in the extraction phase after extraction were used for the quantification of flunitrazepam in plasma and urine samples. The new method not only significantly shortens the extraction time but also provides a new opportunity to determine the free concentration of analyte in biological systems.
Highlights
► Mass transfer dynamics of HF-LPME, SDME and SPME were compared. ► Kinetically calibrated HF-LPME to biological samples was demonstrated. ► Free concentration of flunitrazepam in plasma was determined by 10min KC-HF-LPME.A comprehensive and suitable method for determining major ions from atmospheric particulate matter matrices
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
José S.S. Domingos, Ana Carla D. Regis, João V.S. Santos, Jailson B. de Andrade, Gisele O. da Rocha
The present study proposes an analytical methodology that employs ion chromatography–conductivity detection for simultaneous quantification of inorganic (F−, Cl−, NO3 −, SO4 2−, and PO3 −), monocarboxylate (HCOO−, CH3COO−, propionate, n-butyrate, lactate, and pyruvate), dicarboxylate (oxalate and succinate), and tricarboxylate anions (citrate), as well as crustal cations (Li+, Na+, K+, NH4 +, Ca2+, Mg2+) at low pgm−3 range in airborne particle samples in one single run. The optimized conditions for anions were as follows: 0.6mmolL−1 KOH for 0–14min, 0.6–15mmolL−1 KOH 14–20min, 15–38mmolL−1 KOH during 20–32min and finally returned to 0.6mmolL−1 for a period of 3min, thereafter the eluent flow rate was 0.38mLmin−1. Similarly, for cations, isocratic elution was adjusted to 0.36mLmin−1 at 17.5mmolL−1 H2SO4. LOD ranged 3.0–130pgm−3 and LOQ was within 10–400pgm−3 (Li+ and PO4 3−, respectively) as well as recoveries ranged 89% (Ca2+) to 120% (Li+). Major ions were successfully determined in real PM1 and PM2.5 samples. The method used here was found to be a comprehensive, simple, cheap and reliable procedure for studying ions in particulate matter (PM) samples even those from remote areas or near ecosystem natural conditions.
Source:Journal of Chromatography A, Volume 1266
José S.S. Domingos, Ana Carla D. Regis, João V.S. Santos, Jailson B. de Andrade, Gisele O. da Rocha
The present study proposes an analytical methodology that employs ion chromatography–conductivity detection for simultaneous quantification of inorganic (F−, Cl−, NO3 −, SO4 2−, and PO3 −), monocarboxylate (HCOO−, CH3COO−, propionate, n-butyrate, lactate, and pyruvate), dicarboxylate (oxalate and succinate), and tricarboxylate anions (citrate), as well as crustal cations (Li+, Na+, K+, NH4 +, Ca2+, Mg2+) at low pgm−3 range in airborne particle samples in one single run. The optimized conditions for anions were as follows: 0.6mmolL−1 KOH for 0–14min, 0.6–15mmolL−1 KOH 14–20min, 15–38mmolL−1 KOH during 20–32min and finally returned to 0.6mmolL−1 for a period of 3min, thereafter the eluent flow rate was 0.38mLmin−1. Similarly, for cations, isocratic elution was adjusted to 0.36mLmin−1 at 17.5mmolL−1 H2SO4. LOD ranged 3.0–130pgm−3 and LOQ was within 10–400pgm−3 (Li+ and PO4 3−, respectively) as well as recoveries ranged 89% (Ca2+) to 120% (Li+). Major ions were successfully determined in real PM1 and PM2.5 samples. The method used here was found to be a comprehensive, simple, cheap and reliable procedure for studying ions in particulate matter (PM) samples even those from remote areas or near ecosystem natural conditions.
Highlights
► Ions are major constituents of PM and also ubiquitous in the atmosphere. ► They play an important role in climate change and on human health. ► This proposes determination of 20 ions at low pgm−3 range in one single run. ► Major ions were successfully determined in real atmospheric PM1 and PM2.5 samples. ► This is a comprehensive and reliable procedure for ions study at remote sites.Experimental and theoretical studies on the enantioselectivity of molecularly imprinted polymers prepared with a chiral functional monomer
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
Juan J. Torres, Natalia Gsponer, Cristina L. Ramírez, D. Mariano A. Vera, Hernán A. Montejano, Carlos A. Chesta
A comprehensive study on the enantioseparation of racemic bis[1-phenylethyl]amine (PEA) on a series of molecularly imprinted polymers (MIPs) prepared using the chiral functional monomer (S)-2-(2-methyl-acryloylamino)-3-phenyl propionic acid (MAPP) is reported. MIP-R, MIP-S and MIP-RS, were synthesized separately by imprinting the pure enantiomers (R-, S-PEA) and racemic PEA, respectively, MAPP, EDGMA as crosslinker and chloroform as the porogen. It was found that all MIPs prepared were able to resolve the PEA racemate. Residence times (t r ) and enantioselectivity factors (α) were estimated from typical elution chromatography experiments. Frontal chromatography experiments were conducted to acquire the adsorption isotherms for both enantiomers on the different MIPs (and on the non-imprinted polymer, NIP). The adsorption isotherms were analyzed using the affinity spectrum (AS) and the expectation-maximization (EM) methods. The study also involved the theoretical evaluation of the MAPP/enantiomers interactions in the pre-polymer mixture. The EM method predicts mono- and bimodal distribution of affinity binding sites depending upon the polymer analyzed. Apparently, the enantioseparation process depends on relatively small differences in the stabilization of the diasteroisomeric ion-pairs PEA/MAPP complexes on the surface of the polymers.
Source:Journal of Chromatography A, Volume 1266
Juan J. Torres, Natalia Gsponer, Cristina L. Ramírez, D. Mariano A. Vera, Hernán A. Montejano, Carlos A. Chesta
A comprehensive study on the enantioseparation of racemic bis[1-phenylethyl]amine (PEA) on a series of molecularly imprinted polymers (MIPs) prepared using the chiral functional monomer (S)-2-(2-methyl-acryloylamino)-3-phenyl propionic acid (MAPP) is reported. MIP-R, MIP-S and MIP-RS, were synthesized separately by imprinting the pure enantiomers (R-, S-PEA) and racemic PEA, respectively, MAPP, EDGMA as crosslinker and chloroform as the porogen. It was found that all MIPs prepared were able to resolve the PEA racemate. Residence times (t r ) and enantioselectivity factors (α) were estimated from typical elution chromatography experiments. Frontal chromatography experiments were conducted to acquire the adsorption isotherms for both enantiomers on the different MIPs (and on the non-imprinted polymer, NIP). The adsorption isotherms were analyzed using the affinity spectrum (AS) and the expectation-maximization (EM) methods. The study also involved the theoretical evaluation of the MAPP/enantiomers interactions in the pre-polymer mixture. The EM method predicts mono- and bimodal distribution of affinity binding sites depending upon the polymer analyzed. Apparently, the enantioseparation process depends on relatively small differences in the stabilization of the diasteroisomeric ion-pairs PEA/MAPP complexes on the surface of the polymers.
Highlights
► Impression/separation of a racemic on chiral MIPs. ► Theoretical evaluation of the interactions in the pre-polymer mixture. ► Enantiomeric discrimination mechanisms operating in the different MIPs. ► The isotherms were analyzed using the affinity spectrum and the expectation-maximization methods.Extension of the carotenoid test to superficially porous C18 bonded phases, aromatic ligand types and new classical C18 bonded phases
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
E. Lesellier
The recent introduction of new stationary phases for liquid chromatography based on superficially porous particles, called core–shell or fused-core, dramatically improved the separation performances through very high efficiency, due mainly to reduced eddy diffusion. However, few studies have evaluated the retention and selectivity of C18 phases based on such particles, despite some retention order change reported in literature between some of these phases. The carotenoid test has been developed a few years ago in the goal to compare the chromatographic properties of C18 bonded phases. Based on the analysis of carotenoid pigments by using Supercritical Fluid Chromatography (SFC), it allows, with a single analysis, to measure three main properties of reversed phase chromatography stationary phases: hydrophobicity, polar surface activity and shape selectivity. Previous studies showed the effect of the endcapping treatment, the bonding density, the pore size, and the type of bonding (monomeric vs. polymeric) on these studied properties, and described the classification map used for a direct column comparison. It was applied to ten ODS superficially porous stationary phases, showing varied chromatographic behaviors amongst these phases. As expected, due to the lower specific surface area, these superficially porous phases are less hydrophobic than the fully porous one. In regards of the polar surface activity (residual silanols) and to the shape selectivity, some of these superficially porous phases display close chromatographic properties (Poroshell 120, Halo C18, Ascentis Express, Accucore C18, Nucleoshell C18 on one side and Aeris Wide pore, Aeris peptide and Kinetex XDB on the other side), whereas others, Kinetex C18 and Halo peptide ES C18 display more specific ones. Besides, they can be compared to classical fully porous phases, in the goal to improve method transfer from fully to superficially porous particles. By the way, the paper also report the extension of the test to other ligands such as naphtyl, cholester, phenyl-hexyl, or to the new ODS bonded phases, such as charge surface hybrid phases, High Strength Silica, and Hybrid ones, and also presents results for identical brands using different particle size, such as Luna and Synergi phases. Phenyl-hexyl and napthyl ligands show rather close properties, low hydrophobicity, high polar surface activity and specific shape selectivity, whereas, at the opposite, the cholester phase display a polymeric behavior and a high hydrophobicity. Finally, additional classical (fully porous particles) C18 bonded phases are also reported to complete the data set presented in previous papers.
Source:Journal of Chromatography A, Volume 1266
E. Lesellier
The recent introduction of new stationary phases for liquid chromatography based on superficially porous particles, called core–shell or fused-core, dramatically improved the separation performances through very high efficiency, due mainly to reduced eddy diffusion. However, few studies have evaluated the retention and selectivity of C18 phases based on such particles, despite some retention order change reported in literature between some of these phases. The carotenoid test has been developed a few years ago in the goal to compare the chromatographic properties of C18 bonded phases. Based on the analysis of carotenoid pigments by using Supercritical Fluid Chromatography (SFC), it allows, with a single analysis, to measure three main properties of reversed phase chromatography stationary phases: hydrophobicity, polar surface activity and shape selectivity. Previous studies showed the effect of the endcapping treatment, the bonding density, the pore size, and the type of bonding (monomeric vs. polymeric) on these studied properties, and described the classification map used for a direct column comparison. It was applied to ten ODS superficially porous stationary phases, showing varied chromatographic behaviors amongst these phases. As expected, due to the lower specific surface area, these superficially porous phases are less hydrophobic than the fully porous one. In regards of the polar surface activity (residual silanols) and to the shape selectivity, some of these superficially porous phases display close chromatographic properties (Poroshell 120, Halo C18, Ascentis Express, Accucore C18, Nucleoshell C18 on one side and Aeris Wide pore, Aeris peptide and Kinetex XDB on the other side), whereas others, Kinetex C18 and Halo peptide ES C18 display more specific ones. Besides, they can be compared to classical fully porous phases, in the goal to improve method transfer from fully to superficially porous particles. By the way, the paper also report the extension of the test to other ligands such as naphtyl, cholester, phenyl-hexyl, or to the new ODS bonded phases, such as charge surface hybrid phases, High Strength Silica, and Hybrid ones, and also presents results for identical brands using different particle size, such as Luna and Synergi phases. Phenyl-hexyl and napthyl ligands show rather close properties, low hydrophobicity, high polar surface activity and specific shape selectivity, whereas, at the opposite, the cholester phase display a polymeric behavior and a high hydrophobicity. Finally, additional classical (fully porous particles) C18 bonded phases are also reported to complete the data set presented in previous papers.
Highlights
► The carotenoid test shows different chromatographic behaviors for varied ODS fused core particles. ► Aromatic (phenyl-hexyl, napthyl) and cholesteric ligands are studied. ► Numerous additional ODS phases are classified on a simple map. ► This classification allows a rapid and relevant comparison of their properties.Chromatographic evaluation of a newly designed peptide-silica stationary phase in reverse phase liquid chromatography and hydrophilic interaction liquid chromatography: Mixed mode behavior
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
Sudipta Ray, Makoto Takafuji, Hirotaka Ihara
The short peptide Boc-Phe-Aib-Phe-OH was synthesized and immobilized onto porous silica using grafting methodology. The resulting peptide-bonded silica was characterized using DRIFT-mode FT-IR, elemental analysis, thermogravimetric analysis, solid state C13 NMR spectroscopy and the successful immobilization of the peptide on the silica support was confirmed. This grafted phase was packed into a stainless steel column and used for mixed-mode chromatography such as reversed-phase high-performance liquid chromatography and hydrophilic interaction liquid chromatography for the efficient separation of hydrophobic compounds, small polar molecules, and drug molecules. Compared with ODS and phenyl columns, this new stationary phase shows considerably higher molecular-planarity selectivity towards polyaromatic hydrocarbons and also available for separation of nucleo-analytes and sulfa-drug molecules in a hydrophilic interaction liquid chromatography mode. The multiple interactions induced by polar carbonyl group and hydrophobic phenyl group allow this peptide-modified silica to serve as a multi-mode stationary phase in high performance liquid chromatography.
Source:Journal of Chromatography A, Volume 1266
Sudipta Ray, Makoto Takafuji, Hirotaka Ihara
The short peptide Boc-Phe-Aib-Phe-OH was synthesized and immobilized onto porous silica using grafting methodology. The resulting peptide-bonded silica was characterized using DRIFT-mode FT-IR, elemental analysis, thermogravimetric analysis, solid state C13 NMR spectroscopy and the successful immobilization of the peptide on the silica support was confirmed. This grafted phase was packed into a stainless steel column and used for mixed-mode chromatography such as reversed-phase high-performance liquid chromatography and hydrophilic interaction liquid chromatography for the efficient separation of hydrophobic compounds, small polar molecules, and drug molecules. Compared with ODS and phenyl columns, this new stationary phase shows considerably higher molecular-planarity selectivity towards polyaromatic hydrocarbons and also available for separation of nucleo-analytes and sulfa-drug molecules in a hydrophilic interaction liquid chromatography mode. The multiple interactions induced by polar carbonyl group and hydrophobic phenyl group allow this peptide-modified silica to serve as a multi-mode stationary phase in high performance liquid chromatography.
Highlights
► Novel peptide-silica (Sil-FUF) bio-inspired phase was designed and synthesized. ► The new material is useful for reversed-phase/hydrophilic interaction phase. ► It showed good separation for nucleosides and sulfa compounds in a HILIC mode. ► Chirality recognition ability was also observed. ► Multiple retention mechanism is involved in the chromatographic separation.Chromatographic lipophilicity determination using large volume injections of the solvents non-miscible with the mobile phase
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
Costel Sârbu, Rodica Domnica Naşcu-Briciu, Dorina Casoni, Agata Kot-Wasik, Andrzej Wasik, Jacek Namieśnik
A new perspective in the lipophilicity evaluation through RP-HPLC is permitted by analysis of the retention factor (k) obtained by injecting large volumes of test samples prepared in solvents immiscible with mobile phase. The experiment is carried out on representative groups of compounds with increased toxicity (mycotoxins and alkaloids) and amines with important biological activity (naturally occurring monoamine compounds and related drugs), which are covering a large interval of lipophilicity. The stock solution of each compound was prepared in hexane and the used mobile phases were mixtures of methanol or acetonitrile and water, in suited volume ratio. The injected volume was between 10 and 100μL, while the used stationary phases were RP-18 and RP-8. On both reverse stationary phases the retention factors were linearly decreasing while the injection volume was increasing. In all cases, the linear models were highly statistically significant. On the basis of the obtained results new lipophilicity indices were purposed and discussed. The developed lipophilicity indices and the computationally expressed ones are correlated at a high level of statistical significance.
Source:Journal of Chromatography A, Volume 1266
Costel Sârbu, Rodica Domnica Naşcu-Briciu, Dorina Casoni, Agata Kot-Wasik, Andrzej Wasik, Jacek Namieśnik
A new perspective in the lipophilicity evaluation through RP-HPLC is permitted by analysis of the retention factor (k) obtained by injecting large volumes of test samples prepared in solvents immiscible with mobile phase. The experiment is carried out on representative groups of compounds with increased toxicity (mycotoxins and alkaloids) and amines with important biological activity (naturally occurring monoamine compounds and related drugs), which are covering a large interval of lipophilicity. The stock solution of each compound was prepared in hexane and the used mobile phases were mixtures of methanol or acetonitrile and water, in suited volume ratio. The injected volume was between 10 and 100μL, while the used stationary phases were RP-18 and RP-8. On both reverse stationary phases the retention factors were linearly decreasing while the injection volume was increasing. In all cases, the linear models were highly statistically significant. On the basis of the obtained results new lipophilicity indices were purposed and discussed. The developed lipophilicity indices and the computationally expressed ones are correlated at a high level of statistical significance.
Highlights
► The large volume injection of hexane has been investigated and discussed. ► In all cases, the linear models were highly statistically significant. ► Relevant chromatographic lipophilicity indices have been purposed and validated.Determination of six microcystins and nodularin in surface and drinking waters by on-line solid phase extraction–ultra high pressure liquid chromatography tandem mass spectrometry
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
Eduardo Beltrán, María Ibáñez, Juan Vicente Sancho, Félix Hernández
Microcystins and nodularin are cyclic peptides hepatotoxins produced by cyanobacterial genera (blue-green algae). Toxic cyanobacterial blooms are a worldwide problem, as reported in several countries, like China, Australia, or the United States. Therefore, it is necessary to develop sensitive and reliable analytical methodology to determine this type of toxins in water at parts per billion levels, or even lower. In this work, the potential of solid-phase extraction coupled on-line to ultra-high-pressure liquid chromatography/electrospray tandem mass spectrometry (SPE–UHPLC–MS/MS) has been investigated for the efficient quantification and confirmation of microcystins LR, RR, YR, LY, LW, LF and nodularin in surface and drinking water samples, at sub-ppb levels. The method developed involves the injection of only 1mL of water sample into the on-line SPE–UHPLC–MS/MS system and allows the rapid determination of the compounds selected (8min of chromatographic run), avoiding laborious sample treatment. The method was validated in surface and drinking water by means of recovery experiments at 0.25 and 1μgL−1. Average recoveries (n =5) ranged from 71 to 116%, with relative standard deviations (RSDs) lower than 15%. For microcystins LR, RR, YR and nodularin, a third level was also assayed (0.1μgL−1) obtaining satisfactory data too. Limits of detection between 0.002 and 0.0405μgL−1 were estimated (0.0005μgL−1 for nodularin). The developed method was applied to the analysis of water samples collected in the province of Castellón (Spain). The acquisition of three MS/MS transitions for each compound allowed the unequivocal confirmation of positive samples, which was supported by the accomplishment of ion intensity ratios and retention time when compared with reference standards.
Source:Journal of Chromatography A, Volume 1266
Eduardo Beltrán, María Ibáñez, Juan Vicente Sancho, Félix Hernández
Microcystins and nodularin are cyclic peptides hepatotoxins produced by cyanobacterial genera (blue-green algae). Toxic cyanobacterial blooms are a worldwide problem, as reported in several countries, like China, Australia, or the United States. Therefore, it is necessary to develop sensitive and reliable analytical methodology to determine this type of toxins in water at parts per billion levels, or even lower. In this work, the potential of solid-phase extraction coupled on-line to ultra-high-pressure liquid chromatography/electrospray tandem mass spectrometry (SPE–UHPLC–MS/MS) has been investigated for the efficient quantification and confirmation of microcystins LR, RR, YR, LY, LW, LF and nodularin in surface and drinking water samples, at sub-ppb levels. The method developed involves the injection of only 1mL of water sample into the on-line SPE–UHPLC–MS/MS system and allows the rapid determination of the compounds selected (8min of chromatographic run), avoiding laborious sample treatment. The method was validated in surface and drinking water by means of recovery experiments at 0.25 and 1μgL−1. Average recoveries (n =5) ranged from 71 to 116%, with relative standard deviations (RSDs) lower than 15%. For microcystins LR, RR, YR and nodularin, a third level was also assayed (0.1μgL−1) obtaining satisfactory data too. Limits of detection between 0.002 and 0.0405μgL−1 were estimated (0.0005μgL−1 for nodularin). The developed method was applied to the analysis of water samples collected in the province of Castellón (Spain). The acquisition of three MS/MS transitions for each compound allowed the unequivocal confirmation of positive samples, which was supported by the accomplishment of ion intensity ratios and retention time when compared with reference standards.
Highlights
► On-line SPE–UHPLC–MS/MS method for microcystins and nodularin in waters. ► On-line SPE allows the automation of the procedure, minimizing the sample handling. ► Acquisition of 3 SRM per analyte allowed unequivocal confirmation. ► On-line SPE makes the overall analytical process faster than conventional methods.The use of methyl-β-cyclodextrin to solubilize cholesterol prior to coating onto a C18 stationary phase
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
Shauna A. Charlton, Jason W. Coym
The use of methyl-β-cyclodextrin (MBCD) as a mobile phase additive in reversed-phase liquid chromatography is explored, with the primary goal of using MBCD to solubilize cholesterol in reversed-phase mobile phases for cholesterol-coating of C18 stationary phases. MBCD is shown to increase the solubility of cholesterol in typical reversed-phase mobile phases, especially when the stoichiometric ratio of MBCD to cholesterol exceeds 2:1. Additional equivalents of MBCD further increase solubility, or allow for weaker solvents to be used. The use of weaker solvents allows for larger coating levels of cholesterol onto a C18 stationary phase than are possible without the use of MBCD. Stationary phases coated with cholesterol using MBCD as a co-additive have different selectivity than uncoated phases, especially with regards to phenyl and shape selectivity. Further, the use of MBCD as a mobile phase additive for the elution of cholesterol is examined. It is seen via van’t Hoff analysis that the reduction in retention of cholesterol when MBCD is added to the mobile phase is enthalpically driven.
Source:Journal of Chromatography A, Volume 1266
Shauna A. Charlton, Jason W. Coym
The use of methyl-β-cyclodextrin (MBCD) as a mobile phase additive in reversed-phase liquid chromatography is explored, with the primary goal of using MBCD to solubilize cholesterol in reversed-phase mobile phases for cholesterol-coating of C18 stationary phases. MBCD is shown to increase the solubility of cholesterol in typical reversed-phase mobile phases, especially when the stoichiometric ratio of MBCD to cholesterol exceeds 2:1. Additional equivalents of MBCD further increase solubility, or allow for weaker solvents to be used. The use of weaker solvents allows for larger coating levels of cholesterol onto a C18 stationary phase than are possible without the use of MBCD. Stationary phases coated with cholesterol using MBCD as a co-additive have different selectivity than uncoated phases, especially with regards to phenyl and shape selectivity. Further, the use of MBCD as a mobile phase additive for the elution of cholesterol is examined. It is seen via van’t Hoff analysis that the reduction in retention of cholesterol when MBCD is added to the mobile phase is enthalpically driven.
Highlights
► Methyl-β-cyclodextrin (MBCD) increases solubility of cholesterol in mobile phase. ► MBCD can solubilize cholesterol for coating onto a C18 stationary phase. ► MBCD in mobile phase decreases interaction of cholesterol with stationary phase. ► Coated stationary phases have different selectivity.Rapid metabolite analysis of positron emission tomography radioligands by direct plasma injection combining micellar cleanup with high submicellar liquid chromatography with radiometric detection
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
Ryuji Nakao, Magnus Schou, Christer Halldin
A column-switching liquid chromatographic (LC) system was developed for the radiometabolite analysis of positron emission tomography (PET) radioligands in plasma employing direct injection. This system involves (1) micellar cleanup using a short capture column with a micellar mobile phase for submitting plasma directly into the system, (2) fast-micellar liquid chromatography utilizing a small particle size (2.5μm) analysis column under high submicellar condition for improving sensitivity, resolution and speed of analysis and (3) highly sensitive flow-through β+ detection for online measurement of radioligands and their radiometabolites. This system enabled highly sensitive radiometric analysis at the lowest detection limit of about 1Becquerel (Bq) for 11C-labelled compounds with a high temporal resolution of <4.0min without any pre-treatment of plasma. Finally, this novel method could be successfully applied to study the radiometabolism for various PET radioligands and provided reliable determination in both human and monkey plasma.
Source:Journal of Chromatography A, Volume 1266
Ryuji Nakao, Magnus Schou, Christer Halldin
A column-switching liquid chromatographic (LC) system was developed for the radiometabolite analysis of positron emission tomography (PET) radioligands in plasma employing direct injection. This system involves (1) micellar cleanup using a short capture column with a micellar mobile phase for submitting plasma directly into the system, (2) fast-micellar liquid chromatography utilizing a small particle size (2.5μm) analysis column under high submicellar condition for improving sensitivity, resolution and speed of analysis and (3) highly sensitive flow-through β+ detection for online measurement of radioligands and their radiometabolites. This system enabled highly sensitive radiometric analysis at the lowest detection limit of about 1Becquerel (Bq) for 11C-labelled compounds with a high temporal resolution of <4.0min without any pre-treatment of plasma. Finally, this novel method could be successfully applied to study the radiometabolism for various PET radioligands and provided reliable determination in both human and monkey plasma.
Highlights
► A simple column-switching LC method for the radiometabolite analysis in plasma. ► This system involves micellar cleanup of plasma and high submicellar fast-LC. ► No sample preparation is required. ► Metabolite analysis is completed within 4min with high sensitivity. ► It provides reliable analysis of a large number of samples during PET studies.Plant metabolomics: Resolution and quantification of elusive peaks in liquid chromatography–mass spectrometry profiles of complex plant extracts using multi-way decomposition methods
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
Bekzod Khakimov, José Manuel Amigo, Søren Bak, Søren Balling Engelsen
Previous studies on LC–MS metabolomic profiling of 127 F2 Barbarea vulgaris plants derived from a cross of parental glabrous (G) and pubescent (P) type, revealed four triterpenoid saponins (hederagenin cellobioside, oleanolic acid cellobioside, epihederagenin cellobioside, and gypsogenin cellobioside) that correlated with resistance of plants against the insect herbivore, Phyllotreta nemorum. In this study, for the first time, we demonstrate the efficiency of the multi-way decomposition method PARAllel FACtor analysis 2 (PARAFAC2) for exploring complex LC–MS data. PARAFAC2 enabled automated resolution and quantification of several elusive chromatographic peaks (e.g. overlapped, elution time shifted and low s/n ratio), which could not be detected and quantified by conventional chromatographic data analysis. Raw LC–MS data of 127 F2 B. vulgaris plants were arranged in a three-way array (elution time point×mass spectra×samples), divided into 17 different chromatographic intervals and each interval were individually modeled by PARAFAC2. Three main outputs of the PARAFAC2 models described: (1) elution time profile, (2) relative abundance, and (3) pure mass spectra of the resolved peaks modeled from each interval of the chromatographic data. PARAFAC2 scores corresponding to relative abundances of the resolved peaks were extracted and further used for correlation and partial least squares (PLS) analysis. A total of 71 PARAFAC2 components (which correspond to actual peaks, baselines and tails of neighboring peaks) were modeled from 17 different chromatographic retention time intervals of the LC–MS data. In addition to four previously known saponins, correlation- and PLS-analysis resolved five unknown saponin-like compounds that were significantly correlated with insect resistance. The method also enabled a good separation between resistant and susceptible F2 plants. PARAFAC2 spectral loadings corresponding to the pure mass spectra of chromatographic peaks matched well with experimentally recorded mass spectra (correlation based similarity >95%). This enabled to extract pure mass spectra of highly overlapped and low s/n ratio peaks.
Source:Journal of Chromatography A, Volume 1266
Bekzod Khakimov, José Manuel Amigo, Søren Bak, Søren Balling Engelsen
Previous studies on LC–MS metabolomic profiling of 127 F2 Barbarea vulgaris plants derived from a cross of parental glabrous (G) and pubescent (P) type, revealed four triterpenoid saponins (hederagenin cellobioside, oleanolic acid cellobioside, epihederagenin cellobioside, and gypsogenin cellobioside) that correlated with resistance of plants against the insect herbivore, Phyllotreta nemorum. In this study, for the first time, we demonstrate the efficiency of the multi-way decomposition method PARAllel FACtor analysis 2 (PARAFAC2) for exploring complex LC–MS data. PARAFAC2 enabled automated resolution and quantification of several elusive chromatographic peaks (e.g. overlapped, elution time shifted and low s/n ratio), which could not be detected and quantified by conventional chromatographic data analysis. Raw LC–MS data of 127 F2 B. vulgaris plants were arranged in a three-way array (elution time point×mass spectra×samples), divided into 17 different chromatographic intervals and each interval were individually modeled by PARAFAC2. Three main outputs of the PARAFAC2 models described: (1) elution time profile, (2) relative abundance, and (3) pure mass spectra of the resolved peaks modeled from each interval of the chromatographic data. PARAFAC2 scores corresponding to relative abundances of the resolved peaks were extracted and further used for correlation and partial least squares (PLS) analysis. A total of 71 PARAFAC2 components (which correspond to actual peaks, baselines and tails of neighboring peaks) were modeled from 17 different chromatographic retention time intervals of the LC–MS data. In addition to four previously known saponins, correlation- and PLS-analysis resolved five unknown saponin-like compounds that were significantly correlated with insect resistance. The method also enabled a good separation between resistant and susceptible F2 plants. PARAFAC2 spectral loadings corresponding to the pure mass spectra of chromatographic peaks matched well with experimentally recorded mass spectra (correlation based similarity >95%). This enabled to extract pure mass spectra of highly overlapped and low s/n ratio peaks.
Highlights
► New methodology for processing LC–MS metabolomic data is proposed using PARAFAC2. ► Severe chromatographic artifacts were successfully solved by PARAFAC2 modeling. ► Elusive peaks were simultaneously resoled and quantified without data preprocessing. ► Resolved mass spectral profiles of peaks assisted in tentative identification of saponins. ► PARAFAC2 scores of peaks well separated resistant and susceptible B. vulgaris plants.A novel open-tubular capillary electrochromatography using β-cyclodextrin functionalized graphene oxide-magnetic nanocomposites as tunable stationary phase
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
Ru-Ping Liang, Chun-Ming Liu, Xiang-Ying Meng, Jing-Wu Wang, Jian-Ding Qiu
Chip-based enantioselective open-tubular capillary electrochromatography (OT-CEC) with β-cyclodextrin (β-CD) conjugated graphene oxide-magnetic nanocomposites (GO/Fe3O4 NCs) as stationary phase was developed. GO/Fe3O4 NCs with high magnetic responsivity, excellent solubility and high dispersibility in water were prepared through a facile and controllable in situ chemical deposition strategy. β-CD was then adsorbed onto the GO/Fe3O4 surface to form GO/Fe3O4/β-CD NCs which were localized to the pre-nominated position in polydimethylsiloxane (PDMS) microchannels with the help of magnets. The resultant GO/Fe3O4/β-CD NCs not only have the magnetism of Fe3O4 NPs that make them easily manipulated by an external magnetic field, but also have the larger surface which can incorporate much more chiral selector molecules. In addition, the successful β-CD decorations endowed GO/Fe3O4/β-CD NCs with excellent wettability and led to enhanced stability against high ionic strength. Compared with the native PDMS microchip, the modified surfaces exhibited more stable and suppressed electroosmotic mobility, and less nonspecific adsorption toward analytes. Successful baseline separation of tryptophan enantiomers was achieved in less than 50s with a resolution factor of 1.65 utilizing a separation length of 37mm coupled with in-column amperometric detection. Factors that influence the chiral separation resolution were examined. Under the optimized conditions, the proposed modified chip revealed adequate repeatability concerning run-to-run and day-to-day. These results show that the use of GO/Fe3O4/β-CD NCs within microfluidic channels hold great promise for a variety of analytical schemes.
Source:Journal of Chromatography A, Volume 1266
Ru-Ping Liang, Chun-Ming Liu, Xiang-Ying Meng, Jing-Wu Wang, Jian-Ding Qiu
Chip-based enantioselective open-tubular capillary electrochromatography (OT-CEC) with β-cyclodextrin (β-CD) conjugated graphene oxide-magnetic nanocomposites (GO/Fe3O4 NCs) as stationary phase was developed. GO/Fe3O4 NCs with high magnetic responsivity, excellent solubility and high dispersibility in water were prepared through a facile and controllable in situ chemical deposition strategy. β-CD was then adsorbed onto the GO/Fe3O4 surface to form GO/Fe3O4/β-CD NCs which were localized to the pre-nominated position in polydimethylsiloxane (PDMS) microchannels with the help of magnets. The resultant GO/Fe3O4/β-CD NCs not only have the magnetism of Fe3O4 NPs that make them easily manipulated by an external magnetic field, but also have the larger surface which can incorporate much more chiral selector molecules. In addition, the successful β-CD decorations endowed GO/Fe3O4/β-CD NCs with excellent wettability and led to enhanced stability against high ionic strength. Compared with the native PDMS microchip, the modified surfaces exhibited more stable and suppressed electroosmotic mobility, and less nonspecific adsorption toward analytes. Successful baseline separation of tryptophan enantiomers was achieved in less than 50s with a resolution factor of 1.65 utilizing a separation length of 37mm coupled with in-column amperometric detection. Factors that influence the chiral separation resolution were examined. Under the optimized conditions, the proposed modified chip revealed adequate repeatability concerning run-to-run and day-to-day. These results show that the use of GO/Fe3O4/β-CD NCs within microfluidic channels hold great promise for a variety of analytical schemes.
Highlights
► Chip-based OT-CEC with magnetic GO/Fe3O4/β-CD conjugates as stationary phase was fabricated. ► GO/Fe3O4 NCs showed high magnetic responsivity, excellent solubility and high dispersibility in water. ► GO/Fe3O4 nanocomposites greatly increased the β-CD phase ratio in OT-CEC. ► This protocol simplified the stationary phase fabrication of chip-based OT-CEC microdevice.Micellar Electrokinetic Chromatography with Laser Induced Detection and liquid chromatography tandem mass-spectrometry-based desmosine assays in urine of patients with Chronic Obstructive Pulmonary Disease: A comparative analysis
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
Fabio Ferrari, Marco Fumagalli, Paolo Piccinini, Jan Stolk, Maurizio Luisetti, Simona Viglio, Carmine Tinelli, Paolo Iadarola
Evidences accumulated over the past years that desmosines could be attractive indicators of elastic fibre degradation in Chronic Obstructive Pulmonary Disease have raised substantial interest with the development of reliable assays to measure their concentration in body fluids. It is a firm belief of researchers working in this field that accurate assessment of desmosine concentration would improve the understanding of elastin metabolism disorders and allow these cross-links to become a useful tool in the diagnosis and clinical management of these diseases. From among the variety of techniques available on the market, HPLC; CE and LC–MS have proved to be successful tools for measuring desmosines in biological fluids. However, differences in the analytical performance of methods may hinder the comparability of data, thus limiting the analytical strength and clinical utility of methods themselves. To address the relative contribution of different factors to the exact quantification of desmosines, the full potential of MEKC-LIF and LC–MS, the two systems that better than others offer more selective and sensitive detection for desmosine analysis, was studied on 56 urine samples. The results of this systematic comparative study underline the significant benefits of LC–MS over MEKC-LIF in terms of precision and sensitivity. Nevertheless, MEKC-LIF could be an attractive alternative in routine laboratories lacking the LC–MS instrumentation and skills to run these methods.
Source:Journal of Chromatography A, Volume 1266
Fabio Ferrari, Marco Fumagalli, Paolo Piccinini, Jan Stolk, Maurizio Luisetti, Simona Viglio, Carmine Tinelli, Paolo Iadarola
Evidences accumulated over the past years that desmosines could be attractive indicators of elastic fibre degradation in Chronic Obstructive Pulmonary Disease have raised substantial interest with the development of reliable assays to measure their concentration in body fluids. It is a firm belief of researchers working in this field that accurate assessment of desmosine concentration would improve the understanding of elastin metabolism disorders and allow these cross-links to become a useful tool in the diagnosis and clinical management of these diseases. From among the variety of techniques available on the market, HPLC; CE and LC–MS have proved to be successful tools for measuring desmosines in biological fluids. However, differences in the analytical performance of methods may hinder the comparability of data, thus limiting the analytical strength and clinical utility of methods themselves. To address the relative contribution of different factors to the exact quantification of desmosines, the full potential of MEKC-LIF and LC–MS, the two systems that better than others offer more selective and sensitive detection for desmosine analysis, was studied on 56 urine samples. The results of this systematic comparative study underline the significant benefits of LC–MS over MEKC-LIF in terms of precision and sensitivity. Nevertheless, MEKC-LIF could be an attractive alternative in routine laboratories lacking the LC–MS instrumentation and skills to run these methods.
Direct and simultaneous determination of trace-level carbon tetrachloride, peroxyacetyl nitrate, and peroxypropionyl nitrate using gas chromatography-electron capture detection
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
Gen Zhang, Yujing Mu, Junfeng Liu, Abdelwahid Mellouki
Gas chromatography equipped with electron capture detector (GC-ECD) has been widely used for detecting atmospheric peroxyacetyl nitrate (PAN) and peroxypropionyl nitrate (PPN). However, to the best of our knowledge, only a few capillary columns have been adopted for separation to achieve the direct and simultaneous analysis of the two atmospheric pollutants. This paper demonstrates a novel method for directly and simultaneously measuring atmospheric carbon tetrachloride (CCl4), PAN, and PPN using GC-ECD with a DB-1 separation column. The responses of the GC-ECD to PAN, PPN, and CCl4 were individually calibrated by using gas mixtures prepared via volatilization of synthesized solutions of PAN and PPN or high-purity CCl4 reagent in a Teflon Bag. The concentrations of PAN and PPN in the synthesized solutions were quantified by ion chromatography (IC). Further calibration of the GC-ECD for PAN was conducted by in situ photochemical formation of gaseous PAN which was quantified by a NO x analyzer. The two calibration methods agreed well with each other, and the overall uncertainties for measuring atmospheric PAN were estimated to be ±13% and ±15% based on the calibrations of IC and NO x , respectively. The detection limits (three times the signal to noise ratio) for PAN, PPN, and CCl4 were estimated to be 22, 36, and 5pptv (parts per trillion by volume), respectively. The atmospheric concentrations of these compounds were measured for several days in August in Beijing, and the values obtained in this study were found to be in good agreement with the data reported in the literature for Beijing using other GC-ECD methods.
Source:Journal of Chromatography A, Volume 1266
Gen Zhang, Yujing Mu, Junfeng Liu, Abdelwahid Mellouki
Gas chromatography equipped with electron capture detector (GC-ECD) has been widely used for detecting atmospheric peroxyacetyl nitrate (PAN) and peroxypropionyl nitrate (PPN). However, to the best of our knowledge, only a few capillary columns have been adopted for separation to achieve the direct and simultaneous analysis of the two atmospheric pollutants. This paper demonstrates a novel method for directly and simultaneously measuring atmospheric carbon tetrachloride (CCl4), PAN, and PPN using GC-ECD with a DB-1 separation column. The responses of the GC-ECD to PAN, PPN, and CCl4 were individually calibrated by using gas mixtures prepared via volatilization of synthesized solutions of PAN and PPN or high-purity CCl4 reagent in a Teflon Bag. The concentrations of PAN and PPN in the synthesized solutions were quantified by ion chromatography (IC). Further calibration of the GC-ECD for PAN was conducted by in situ photochemical formation of gaseous PAN which was quantified by a NO x analyzer. The two calibration methods agreed well with each other, and the overall uncertainties for measuring atmospheric PAN were estimated to be ±13% and ±15% based on the calibrations of IC and NO x , respectively. The detection limits (three times the signal to noise ratio) for PAN, PPN, and CCl4 were estimated to be 22, 36, and 5pptv (parts per trillion by volume), respectively. The atmospheric concentrations of these compounds were measured for several days in August in Beijing, and the values obtained in this study were found to be in good agreement with the data reported in the literature for Beijing using other GC-ECD methods.
Highlights
► A method for simultaneously analyzing atmospheric CCl4, PAN and PPN was developed. ► The method consisted of GC-ECD with DB-1 capillary column. ► The response of GC-ECD to PAN was calibrated by IC and NO x analyzer, respectively. ► Field measurements were also conducted by using the developed method.Fast, high peak capacity separations in comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
Brian D. Fitz, Ryan B. Wilson, Brendon A. Parsons, Jamin C. Hoggard, Robert E. Synovec
Peak capacity production is substantially improved for two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC–TOFMS) and applied to the fast separation of a 28 component liquid test mixture, and two complex vapor samples (a 65 component volatile organic compound test mixture, and the headspace of warm ground coffee beans). A high peak capacity is achieved in a short separation time by selecting appropriate experimental conditions based on theoretical modeling of on-column band broadening, and by reducing the off-column band broadening by applying a narrow, concentrated injection pulse onto the primary column using high-speed cryo-focusing injection (HSCFI), referred to as thermal injection. A long, relatively narrow open tubular capillary column (20m, 100μm inner diameter (i.d.) with a 0.4μm film thickness to benefit column capacity) was used as the primary column. The initial flow rate was 2ml/min (60cm/s average linear flow velocity) which is slightly below the optimal average linear gas velocity of 83cm/s, due to the flow rate constraint of the TOFMS vacuum system. The oven temperature programming rate was 30°C/min. The secondary column (1.8m, 100μm i.d. with a 0.1μm film thickness) provided a relatively high peak capacity separation, concurrent with a significantly shorter modulation period, P M, than commonly applied with the commercial instrument. With this GC×GC–TOFMS instrumental platform, compounds in the 28 component liquid test mixture provided a ∼7min separation (with a ∼6.5min separation time window), producing average peak widths of ∼600ms full width half maximum (FWHM), resulting in a peak capacity on the primary column of ∼400peaks (at unit resolution). Using a secondary column with a 500ms P M, average peak widths of ∼20ms FWHM were achieved, thus providing a peak capacity of 15peaks on the second dimension. Overall, an ideal orthogonal GC×GC peak capacity of ∼6000peaks (at unit resolution) was achieved (or a β-corrected orthogonal peak capacity of ∼4400, at an average modulation ratio, M R, of ∼2). This corresponds to an ideal orthogonal peak capacity production of ∼1000peaks/min (or ∼700peaks/min, β-corrected). For comparison, standard split/split-less injection techniques with a 1:100 split, when combined with standard GC×GC conditions typically provide a peak capacity production of ∼100peaks/min, hence the instrumental platform we report provides a ∼7-fold to 10-fold improvement.
Source:Journal of Chromatography A, Volume 1266
Brian D. Fitz, Ryan B. Wilson, Brendon A. Parsons, Jamin C. Hoggard, Robert E. Synovec
Peak capacity production is substantially improved for two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC–TOFMS) and applied to the fast separation of a 28 component liquid test mixture, and two complex vapor samples (a 65 component volatile organic compound test mixture, and the headspace of warm ground coffee beans). A high peak capacity is achieved in a short separation time by selecting appropriate experimental conditions based on theoretical modeling of on-column band broadening, and by reducing the off-column band broadening by applying a narrow, concentrated injection pulse onto the primary column using high-speed cryo-focusing injection (HSCFI), referred to as thermal injection. A long, relatively narrow open tubular capillary column (20m, 100μm inner diameter (i.d.) with a 0.4μm film thickness to benefit column capacity) was used as the primary column. The initial flow rate was 2ml/min (60cm/s average linear flow velocity) which is slightly below the optimal average linear gas velocity of 83cm/s, due to the flow rate constraint of the TOFMS vacuum system. The oven temperature programming rate was 30°C/min. The secondary column (1.8m, 100μm i.d. with a 0.1μm film thickness) provided a relatively high peak capacity separation, concurrent with a significantly shorter modulation period, P M, than commonly applied with the commercial instrument. With this GC×GC–TOFMS instrumental platform, compounds in the 28 component liquid test mixture provided a ∼7min separation (with a ∼6.5min separation time window), producing average peak widths of ∼600ms full width half maximum (FWHM), resulting in a peak capacity on the primary column of ∼400peaks (at unit resolution). Using a secondary column with a 500ms P M, average peak widths of ∼20ms FWHM were achieved, thus providing a peak capacity of 15peaks on the second dimension. Overall, an ideal orthogonal GC×GC peak capacity of ∼6000peaks (at unit resolution) was achieved (or a β-corrected orthogonal peak capacity of ∼4400, at an average modulation ratio, M R, of ∼2). This corresponds to an ideal orthogonal peak capacity production of ∼1000peaks/min (or ∼700peaks/min, β-corrected). For comparison, standard split/split-less injection techniques with a 1:100 split, when combined with standard GC×GC conditions typically provide a peak capacity production of ∼100peaks/min, hence the instrumental platform we report provides a ∼7-fold to 10-fold improvement.
Highlights
► Peak capacity and peak capacity production are significantly improved for GC×GC–TOFMS. ► A peak capacity of ∼6000 was obtained in ∼6min in a GC×GC–TOFMS separation. ► Primary column peaks were ∼600ms FWHM and secondary column peaks were ∼20ms FWHM. ► Cryo-focusing thermal injection was utilized for a narrow injection onto the primary column. ► The instrument was applied to the separation of the headspace of warm, ground coffee beans.Compounds for expanding the descriptor space for characterizing separation systems
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
Thushara Karunasekara, Colin F. Poole
A combination of gas chromatography and liquid–liquid partitions in totally organic biphasic systems is used to determine descriptor values for compounds of low volatility suitable for characterizing open tubular columns at high temperatures. The descriptor database of varied compounds includes several difficult to determine by conventional techniques due to their low water solubility or stability. The descriptor database facilitates an expansion of the descriptor space and compound variation for characterizing separation systems. As an application the descriptor database is used to determine the system constants for SPB-Octyl, HP-5, Rxi-5Sil MS, Rtx-440, and Rtx-OPP for the temperature range 200–300°C. As an example of the broader affect of temperature on column selectivity the variation of the system constants for Rtx-440 over the temperature range 60–300°C is described in detail. These studies demonstrate the persistence of polar interactions to the highest temperature studied and that at high temperatures selectivity differences persist for moderately polar stationary phases.
Source:Journal of Chromatography A, Volume 1266
Thushara Karunasekara, Colin F. Poole
A combination of gas chromatography and liquid–liquid partitions in totally organic biphasic systems is used to determine descriptor values for compounds of low volatility suitable for characterizing open tubular columns at high temperatures. The descriptor database of varied compounds includes several difficult to determine by conventional techniques due to their low water solubility or stability. The descriptor database facilitates an expansion of the descriptor space and compound variation for characterizing separation systems. As an application the descriptor database is used to determine the system constants for SPB-Octyl, HP-5, Rxi-5Sil MS, Rtx-440, and Rtx-OPP for the temperature range 200–300°C. As an example of the broader affect of temperature on column selectivity the variation of the system constants for Rtx-440 over the temperature range 60–300°C is described in detail. These studies demonstrate the persistence of polar interactions to the highest temperature studied and that at high temperatures selectivity differences persist for moderately polar stationary phases.
Highlights
► Descriptors for compounds of low water solubility and low volatility. ► First time characterization of stationary phases at high temperatures. ► Demonstrates persistence of polar interactions at high temperatures.Compensation for matrix effects in the gas chromatography–mass spectrometry analysis of 186 pesticides in tea matrices using analyte protectants
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
Yan Li, Xi Chen, Chunlin Fan, Guofang Pang
A gas chromatography–mass spectrometry (GC–MS) analytical method was developed for simultaneously determining 186 pesticides in tea matrices using analyte protectants to counteract the matrix-induced effect. The matrix effects were evaluated for green, oolong and black tea, representing unfermented, partially fermented and completely fermented teas respectively and depending on the type of tea, 72%, 94% and 94% of the pesticides presented strong response enhancement effect. Several analyte protectants as well as certain combinations of these protectants were evaluated to check their compensation effects. A mixture of triglycerol and d-ribonic acid-γ-lactone (both at 2mg/mL in the injected samples) was found to be the most effective in improving the chromatographic behavior of the 186 pesticides. More than 96% of the 186 pesticides achieved recoveries within the range of 70–120% when using the selected mixture of analyte protectants. The simple addition of analyte protectants offers a more convenient solution to overcome matrix effects, results in less active sites compared to matrix-matched standardization and can be an effective approach to compensate for matrix effects in the GC–MS analysis of pesticide residues.
Source:Journal of Chromatography A, Volume 1266
Yan Li, Xi Chen, Chunlin Fan, Guofang Pang
A gas chromatography–mass spectrometry (GC–MS) analytical method was developed for simultaneously determining 186 pesticides in tea matrices using analyte protectants to counteract the matrix-induced effect. The matrix effects were evaluated for green, oolong and black tea, representing unfermented, partially fermented and completely fermented teas respectively and depending on the type of tea, 72%, 94% and 94% of the pesticides presented strong response enhancement effect. Several analyte protectants as well as certain combinations of these protectants were evaluated to check their compensation effects. A mixture of triglycerol and d-ribonic acid-γ-lactone (both at 2mg/mL in the injected samples) was found to be the most effective in improving the chromatographic behavior of the 186 pesticides. More than 96% of the 186 pesticides achieved recoveries within the range of 70–120% when using the selected mixture of analyte protectants. The simple addition of analyte protectants offers a more convenient solution to overcome matrix effects, results in less active sites compared to matrix-matched standardization and can be an effective approach to compensate for matrix effects in the GC–MS analysis of pesticide residues.
Highlights
► Most of the pesticides presented strong response enhancement effects in green, oolong and black tea. ► Effects of eleven analyte protectants on compensating the matrix effect were evaluated. ► Mixture of triglycerol and d-ribonic acid-γ-lactone was most effective for the 186 pesticides in tea matrix.High-throughput simultaneous analysis of pesticides by supercritical fluid chromatography/tandem mass spectrometry
09 November 2012,
09:11:23
Publication year:
2012
Source:Journal of Chromatography A, Volume 1266
Megumi Ishibashi, Takashi Ando, Miho Sakai, Atsuki Matsubara, Takato Uchikata, Eiichiro Fukusaki, Takeshi Bamba
Combination techniques such as gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS) are commonly used for pesticide residue analysis, but there is no reported method for the simultaneous analysis of multiple pesticides in a sample using a single instrument. Supercritical fluid chromatography (SFC) offers high resolution at high flow rates and various separation modes and hence may aid the rapid simultaneous analysis of pesticide. We developed an SFC/MS/MS method and analyzed 17 pesticides with a wide range of polarities (log P ow =−4.6 to 7.05) and molecular weights (112.1–888.6) within 11min using a polar-embedded reversed-phase column. To the best of our knowledge, there is no previous report on the SFC analysis of a wide variety of compounds, including highly hydrophilic ones. By SFC, diquat dibromide (log P ow =−4.6), together with cypermethrin (log P ow =6.6) and tralomethrin (log P ow =5.05), could be detected in the presence of various other pesticides using a single mobile phase. SFC/MS allows for the rapid and simultaneous analysis of low concentrations (ng/L levels) of pesticides that typically need to be analyzed by GC/MS and LC/MS separately.
Source:Journal of Chromatography A, Volume 1266
Megumi Ishibashi, Takashi Ando, Miho Sakai, Atsuki Matsubara, Takato Uchikata, Eiichiro Fukusaki, Takeshi Bamba
Combination techniques such as gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS) are commonly used for pesticide residue analysis, but there is no reported method for the simultaneous analysis of multiple pesticides in a sample using a single instrument. Supercritical fluid chromatography (SFC) offers high resolution at high flow rates and various separation modes and hence may aid the rapid simultaneous analysis of pesticide. We developed an SFC/MS/MS method and analyzed 17 pesticides with a wide range of polarities (log P ow =−4.6 to 7.05) and molecular weights (112.1–888.6) within 11min using a polar-embedded reversed-phase column. To the best of our knowledge, there is no previous report on the SFC analysis of a wide variety of compounds, including highly hydrophilic ones. By SFC, diquat dibromide (log P ow =−4.6), together with cypermethrin (log P ow =6.6) and tralomethrin (log P ow =5.05), could be detected in the presence of various other pesticides using a single mobile phase. SFC/MS allows for the rapid and simultaneous analysis of low concentrations (ng/L levels) of pesticides that typically need to be analyzed by GC/MS and LC/MS separately.
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