A new
issue of this journal has just been published. To see abstracts of the papers
it contains (with links through to the full papers) click here:
Selected papers from the latest issue:
The van Deemter equation: Assumptions, limits, and adjustment to modern high performance liquid chromatography
18 July 2013,
09:11:36
Publication date: 9 August
2013
Source:Journal of Chromatography A, Volume 1302
Author(s): Fabrice Gritti , Georges Guiochon
The fundamental assumptions of the van Deemter height equivalent to a theoretical plate (HETP) equation were formulated nearly 60 years ago in its rigorous final mathematical derivation in 1956. The limit of applicability of this classical theory of band broadening in chromatographic columns is discussed on the basis of accurate measurements of diffusion coefficients (in the bulk, in particles, and in column beds), of peak moments in both RPLC and HILIC, on the recent numerical solution of the Navier–Stokes equation and on the results of the simulation of the advection–diffusion transport in the bulk region of computer-generated random packed beds. A result of this discussion is that serious errors are made in the interpretations of the mass transfer mechanism in HILIC and RPLC that are based on the use of the original van Deemter expressions of the longitudinal diffusion coefficient through packed bed, of the mass transfer resistance in the mobile phase, and of the mass transfer resistance in the stationary phase. These errors are discussed and quantitatively assessed. Physically acceptable and relevant expressions are proposed to account for the true mass transfer mechanism in packed columns.
Source:Journal of Chromatography A, Volume 1302
Author(s): Fabrice Gritti , Georges Guiochon
The fundamental assumptions of the van Deemter height equivalent to a theoretical plate (HETP) equation were formulated nearly 60 years ago in its rigorous final mathematical derivation in 1956. The limit of applicability of this classical theory of band broadening in chromatographic columns is discussed on the basis of accurate measurements of diffusion coefficients (in the bulk, in particles, and in column beds), of peak moments in both RPLC and HILIC, on the recent numerical solution of the Navier–Stokes equation and on the results of the simulation of the advection–diffusion transport in the bulk region of computer-generated random packed beds. A result of this discussion is that serious errors are made in the interpretations of the mass transfer mechanism in HILIC and RPLC that are based on the use of the original van Deemter expressions of the longitudinal diffusion coefficient through packed bed, of the mass transfer resistance in the mobile phase, and of the mass transfer resistance in the stationary phase. These errors are discussed and quantitatively assessed. Physically acceptable and relevant expressions are proposed to account for the true mass transfer mechanism in packed columns.
Solvent-impregnated agarose gel liquid phase microextraction of polycyclic aromatic hydrocarbons in water
18 July 2013,
09:11:36
Publication date: 9 August
2013
Source:Journal of Chromatography A, Volume 1302
Author(s): Saw Hong Loh , Mohd Marsin Sanagi , Wan Aini Wan Ibrahim , Mohamed Noor Hasan
A new microextraction procedure termed agarose gel liquid phase microextraction (AG-LPME) combined with gas chromatography–mass spectrometry (GC–MS) was developed for the determination of selected polycyclic aromatic hydrocarbons (PAHs) in water. The technique utilized an agarose gel disc impregnated with the acceptor phase (1-octanol). The extraction procedure was performed by allowing the solvent-impregnated agarose gel disc to tumble freely in the stirred sample solution. After extraction, the agarose gel disc was removed and subjected to centrifugation to disrupt its framework and to release the impregnated solvent, which was subsequently withdrawn and injected into the GC–MS for analysis. Under optimized extraction conditions, the new method offered high enrichment factors (89–177), trace level LODs (9–14ngL−1) and efficient extraction with good relative recoveries in the range of 93.3–108.2% for spiked drinking water samples. AG-LPME did not exhibit any problems related to solvent dissolution, and it provided high extraction efficiencies that were comparable to those of hollow fiber liquid phase microextraction (HF-LPME) and significantly higher than those of agarose film liquid phase microextraction (AF-LPME). This technique employed a microextraction format and utilized an environmentally compatible solvent holder that supported the green chemistry concept.
Source:Journal of Chromatography A, Volume 1302
Author(s): Saw Hong Loh , Mohd Marsin Sanagi , Wan Aini Wan Ibrahim , Mohamed Noor Hasan
A new microextraction procedure termed agarose gel liquid phase microextraction (AG-LPME) combined with gas chromatography–mass spectrometry (GC–MS) was developed for the determination of selected polycyclic aromatic hydrocarbons (PAHs) in water. The technique utilized an agarose gel disc impregnated with the acceptor phase (1-octanol). The extraction procedure was performed by allowing the solvent-impregnated agarose gel disc to tumble freely in the stirred sample solution. After extraction, the agarose gel disc was removed and subjected to centrifugation to disrupt its framework and to release the impregnated solvent, which was subsequently withdrawn and injected into the GC–MS for analysis. Under optimized extraction conditions, the new method offered high enrichment factors (89–177), trace level LODs (9–14ngL−1) and efficient extraction with good relative recoveries in the range of 93.3–108.2% for spiked drinking water samples. AG-LPME did not exhibit any problems related to solvent dissolution, and it provided high extraction efficiencies that were comparable to those of hollow fiber liquid phase microextraction (HF-LPME) and significantly higher than those of agarose film liquid phase microextraction (AF-LPME). This technique employed a microextraction format and utilized an environmentally compatible solvent holder that supported the green chemistry concept.
Ultrasound-assisted dispersive liquid–liquid microextraction plus simultaneous silylation for rapid determination of salicylate and benzophenone-type ultraviolet filters in aqueous samples
18 July 2013,
09:11:36
Publication date: 9 August
2013
Source:Journal of Chromatography A, Volume 1302
Author(s): Jen-Wen Wu , Hsin-Chang Chen , Wang-Hsien Ding
A rapid procedure, using minimal amounts of solvent, for the reliable determination of five salicylate and benzophenone-type ultraviolet (UV) filters: ethylhexyl salicylate (EHS), 3,3,5-trimethyl-cyclohexyl salicylate (HMS), 2-hydroxy-4-methoxybenzophenone (BP-3), 2,4-dihydroxy-benzophenone (BP-1) and 2,2′-dihydroxy-4-methoxybenzophenone (BP-8), in aqueous samples is described. The method involves an ultrasound-assisted dispersive liquid–liquid microextraction (UA-DLLME) plus simultaneous silylation prior to their determination by gas chromatography–mass spectrometry (GC–MS). The parameters affecting the extraction and derivatization efficiency of the target UV filters from aqueous samples were systematically investigated and the conditions optimized. The optimal silylation and extraction conditions involved the rapid injection of a mixture of 750μL of acetone (as a dispersant), 15μL of tetrachloroethylene (as an extractant), and 20μL of BSTFA (as a derivatizing agent) into a 10-mL volume of aqueous samples (pH 7.0) containing 0.5g of sodium chloride in a glass tube with a conical bottom. After ultrasonication for 2.0min and centrifugation at 5000rpm (10min), the sedimented phase 5.0μL was directly introduced into the GC–MS. The limits of quantitation (LOQs) were less than 6ng/L. The precision for these analytes, as indicated by the relative standard deviations (RSDs), was less than 9% for both intra- and inter-day analysis. Accuracy, expressed as the mean extraction recovery, was between 74 and 92%. The method was then applied to environmental aqueous samples, using a standard addition method, showing the occurrence of BP-3 in samples of both river water and municipal wastewater treatment plant (MWTP) effluents.
Source:Journal of Chromatography A, Volume 1302
Author(s): Jen-Wen Wu , Hsin-Chang Chen , Wang-Hsien Ding
A rapid procedure, using minimal amounts of solvent, for the reliable determination of five salicylate and benzophenone-type ultraviolet (UV) filters: ethylhexyl salicylate (EHS), 3,3,5-trimethyl-cyclohexyl salicylate (HMS), 2-hydroxy-4-methoxybenzophenone (BP-3), 2,4-dihydroxy-benzophenone (BP-1) and 2,2′-dihydroxy-4-methoxybenzophenone (BP-8), in aqueous samples is described. The method involves an ultrasound-assisted dispersive liquid–liquid microextraction (UA-DLLME) plus simultaneous silylation prior to their determination by gas chromatography–mass spectrometry (GC–MS). The parameters affecting the extraction and derivatization efficiency of the target UV filters from aqueous samples were systematically investigated and the conditions optimized. The optimal silylation and extraction conditions involved the rapid injection of a mixture of 750μL of acetone (as a dispersant), 15μL of tetrachloroethylene (as an extractant), and 20μL of BSTFA (as a derivatizing agent) into a 10-mL volume of aqueous samples (pH 7.0) containing 0.5g of sodium chloride in a glass tube with a conical bottom. After ultrasonication for 2.0min and centrifugation at 5000rpm (10min), the sedimented phase 5.0μL was directly introduced into the GC–MS. The limits of quantitation (LOQs) were less than 6ng/L. The precision for these analytes, as indicated by the relative standard deviations (RSDs), was less than 9% for both intra- and inter-day analysis. Accuracy, expressed as the mean extraction recovery, was between 74 and 92%. The method was then applied to environmental aqueous samples, using a standard addition method, showing the occurrence of BP-3 in samples of both river water and municipal wastewater treatment plant (MWTP) effluents.
Hyperbranched polymers containing stereocontorted cores as on-line solid-phase microextraction adsorbent for polycyclic aromatic hydrocarbons
18 July 2013,
09:11:36
Publication date: 9 August
2013
Source:Journal of Chromatography A, Volume 1302
Author(s): Xingmei Guan , Chuande Zhao , Xiaoyan Liu , Haixia Zhang
A polymer monolith column was prepared using click chemistry for on-line solid phase microextraction of polycyclic aromatic hydrocarbons (PAHs), using 2,2′,7,7′-tetraethynyl-9,9′-spirobifluorene(TES) and 1,4-bis(6-azidoalkoxy)benzene (BAB) as monomers, and Cu(PPh3)3Br as the catalyst. The polymer with spirocyclic cross-links was porous and presented an appropriate interspace of PAHs. Enrichment of PAHs, in the range of 100 to more than 1000 times, was due to the π–π stacking interaction and the effect of small size. The factors affecting the on-line microextraction efficiency were optimized, and the analytical conditions were evaluated to ensure reliability.
Source:Journal of Chromatography A, Volume 1302
Author(s): Xingmei Guan , Chuande Zhao , Xiaoyan Liu , Haixia Zhang
A polymer monolith column was prepared using click chemistry for on-line solid phase microextraction of polycyclic aromatic hydrocarbons (PAHs), using 2,2′,7,7′-tetraethynyl-9,9′-spirobifluorene(TES) and 1,4-bis(6-azidoalkoxy)benzene (BAB) as monomers, and Cu(PPh3)3Br as the catalyst. The polymer with spirocyclic cross-links was porous and presented an appropriate interspace of PAHs. Enrichment of PAHs, in the range of 100 to more than 1000 times, was due to the π–π stacking interaction and the effect of small size. The factors affecting the on-line microextraction efficiency were optimized, and the analytical conditions were evaluated to ensure reliability.
Targeting high-performance liquid chromatography–high-resolution mass spectrometry–solid-phase extraction–nuclear magnetic resonance analysis with high-resolution radical scavenging profiles—Bioactive secondary metabolites from the endophytic fungus Penicillium namyslowskii
18 July 2013,
09:11:36
Publication date: 9 August
2013
Source:Journal of Chromatography A, Volume 1302
Author(s): Sileshi G. Wubshet , Nils T. Nyberg , Mysore V. Tejesvi , Anna Maria Pirttilä , Marena Kajula , Sampo Mattila , Dan Staerk
The high-resolution radical scavenging profile of an extract of the endophytic fungus Penicillium namyslowskii was used to target analysis by high-performance liquid chromatography–high-resolution mass spectrometry–solid-phase extraction–nuclear magnetic resonance spectroscopy, i.e., HPLC–HRMS–SPE–NMR, for identification of anti-oxidative secondary metabolites. This revealed the two chromatographic peaks with the highest relative response in the radical scavenging profile to be griseophenone C and peniprequinolone. The HPLC–HRMS–SPE–NMR analysis was performed in the tube-transfer mode using a cryogenically cooled NMR probe designed for 1.7mm NMR tubes. To further explore the potential of the above HPLC–HRMS–SPE–NMR platform for analysis of endophytic extracts, six peaks displaying no radical scavenging activity were also analyzed. This allowed unambiguous identification of six metabolites, i.e., dechlorogriseofulvin, dechlorodehydrogriseofulvin, griseofulvin, dehydrogriseofulvin, mevastatin acid, and mevastatin. The high mass sensitivity of the 1.7mm cryogenically cooled NMR probe allowed for the first time acquisition of direct detected 13C NMR spectra of fungal metabolites, i.e., dechlorogriseofulvin and griseofulvin, directly from crude extract via HPLC–HRMS–SPE–NMR. Dechlorodehydrogriseofulvin was reported for the first time from nature.
Source:Journal of Chromatography A, Volume 1302
Author(s): Sileshi G. Wubshet , Nils T. Nyberg , Mysore V. Tejesvi , Anna Maria Pirttilä , Marena Kajula , Sampo Mattila , Dan Staerk
The high-resolution radical scavenging profile of an extract of the endophytic fungus Penicillium namyslowskii was used to target analysis by high-performance liquid chromatography–high-resolution mass spectrometry–solid-phase extraction–nuclear magnetic resonance spectroscopy, i.e., HPLC–HRMS–SPE–NMR, for identification of anti-oxidative secondary metabolites. This revealed the two chromatographic peaks with the highest relative response in the radical scavenging profile to be griseophenone C and peniprequinolone. The HPLC–HRMS–SPE–NMR analysis was performed in the tube-transfer mode using a cryogenically cooled NMR probe designed for 1.7mm NMR tubes. To further explore the potential of the above HPLC–HRMS–SPE–NMR platform for analysis of endophytic extracts, six peaks displaying no radical scavenging activity were also analyzed. This allowed unambiguous identification of six metabolites, i.e., dechlorogriseofulvin, dechlorodehydrogriseofulvin, griseofulvin, dehydrogriseofulvin, mevastatin acid, and mevastatin. The high mass sensitivity of the 1.7mm cryogenically cooled NMR probe allowed for the first time acquisition of direct detected 13C NMR spectra of fungal metabolites, i.e., dechlorogriseofulvin and griseofulvin, directly from crude extract via HPLC–HRMS–SPE–NMR. Dechlorodehydrogriseofulvin was reported for the first time from nature.
Binding and elution behavior of small deoxyribonucleic acid fragments on a strong anion-exchanger multimodal chromatography resin
18 July 2013,
09:11:36
Publication date: 9 August
2013
Source:Journal of Chromatography A, Volume 1302
Author(s): Tiago Matos , João A. Queiroz , Leif Bülow
The separation behavior of small single-stranded from double-stranded DNA molecules has been determined on a multimodal (mixed-mode) chromatography system. The resin used is a strong anion exchanger which also modulates hydrophobic recognition. The intrinsic differences between single- and double-stranded DNAs concerning charge, hydrophobicity and three-dimensional structure render this form of MMC suitable for separation of the different nucleic acid molecules. All DNAs tested bound strongly to the resin and they could be eluted with increasing NaCl concentrations. Each homopolymeric ssDNA sample resulted in a base-specific elution pattern when using a linear NaCl gradient. The elution order was poly(dA)<poly(dC)<poly(dG)<poly(dT) and this order was dependent on the secondary structure of the molecule. Such differences were not observed for small double-stranded DNAs. Due to the more hydrophobic nature of single-stranded DNA molecules they could be separated from double-stranded DNAs.
Source:Journal of Chromatography A, Volume 1302
Author(s): Tiago Matos , João A. Queiroz , Leif Bülow
The separation behavior of small single-stranded from double-stranded DNA molecules has been determined on a multimodal (mixed-mode) chromatography system. The resin used is a strong anion exchanger which also modulates hydrophobic recognition. The intrinsic differences between single- and double-stranded DNAs concerning charge, hydrophobicity and three-dimensional structure render this form of MMC suitable for separation of the different nucleic acid molecules. All DNAs tested bound strongly to the resin and they could be eluted with increasing NaCl concentrations. Each homopolymeric ssDNA sample resulted in a base-specific elution pattern when using a linear NaCl gradient. The elution order was poly(dA)<poly(dC)<poly(dG)<poly(dT) and this order was dependent on the secondary structure of the molecule. Such differences were not observed for small double-stranded DNAs. Due to the more hydrophobic nature of single-stranded DNA molecules they could be separated from double-stranded DNAs.
Optimizing selectivity during reversed-phase high performance liquid chromatography method development: Prioritizing experimental conditions
18 July 2013,
09:11:36
Publication date: 9 August
2013
Source:Journal of Chromatography A, Volume 1302
Author(s): Lloyd R. Snyder , John W. Dolan
Several different conditions can be varied to improve selectivity for reversed-phase chromatography (RPC). A reexamination of literature data suggests that changes in selectivity due to a change of column or mobile phase pH are largely replicated by changes in temperature or mobile phase composition (concentrations of acetonitrile and/or methanol). This suggests a reconsideration of the role of mobile phase pH and the column during method development.
Source:Journal of Chromatography A, Volume 1302
Author(s): Lloyd R. Snyder , John W. Dolan
Several different conditions can be varied to improve selectivity for reversed-phase chromatography (RPC). A reexamination of literature data suggests that changes in selectivity due to a change of column or mobile phase pH are largely replicated by changes in temperature or mobile phase composition (concentrations of acetonitrile and/or methanol). This suggests a reconsideration of the role of mobile phase pH and the column during method development.
Mass transfer mechanism in hydrophilic interaction chromatography
18 July 2013,
09:11:36
Publication date: 9 August
2013
Source:Journal of Chromatography A, Volume 1302
Author(s): Fabrice Gritti , Georges Guiochon
The mass transfer mechanism in HILIC was investigated in depth. The reduced heights equivalent to a theoretical plate (HETP) of five low molecular weigh compounds with retention factors of −0.05 (slight exclusion from the surface due to the presence of a water-rich layer in which naphthalene is insoluble) to 3.64 were measured at room temperature for a 4.6mm×100mm column packed with 3.5μm 140Å XBridge HILIC particles in a wide range of flow velocities. The mobile phase was a buffered acetonitrile–water mixture (92.5/7.5, v/v). Using a physically reliable model of effective diffusion in binary composite media (Torquato's model), the longitudinal diffusion and solid–liquid mass transfer resistance reduced HETP terms were measured. The reduced short-range eddy dispersion HETP was taken from the literature data. The long-range reduced HETP was directly measured from the subtraction of these HETP terms to the overall HETP measured from moment analysis. In contrast to RPLC, the plots of the reduced HETP versus the reduced velocity depend weakly on the retention factor, due to the constant, low intra-particle diffusivity observed in HILIC. So, the reduced longitudinal diffusion HETP is smaller and the reduced solid–liquid mass transfer resistance HETP is larger in HILIC than in RPLC. Whereas border effects can be concealed in RPLC for retained analytes due to fast radial equilibration across the column diameter, a residual long-range eddy dispersion term persists in 4.6mm I.D. HILIC columns, even at very slow flow rates. Experiments show that the minor differences in the long-range eddy dispersion term between analytes having different retention factors is directly correlated to the reciprocal of their bulk diffusion coefficient. The performance of HILIC columns packed with fine particles is then more sensitive to the inlet sample distribution and to the outlet sample collection than RPLC columns due to the relatively poor radial mixing controlled by lateral diffusion.
Source:Journal of Chromatography A, Volume 1302
Author(s): Fabrice Gritti , Georges Guiochon
The mass transfer mechanism in HILIC was investigated in depth. The reduced heights equivalent to a theoretical plate (HETP) of five low molecular weigh compounds with retention factors of −0.05 (slight exclusion from the surface due to the presence of a water-rich layer in which naphthalene is insoluble) to 3.64 were measured at room temperature for a 4.6mm×100mm column packed with 3.5μm 140Å XBridge HILIC particles in a wide range of flow velocities. The mobile phase was a buffered acetonitrile–water mixture (92.5/7.5, v/v). Using a physically reliable model of effective diffusion in binary composite media (Torquato's model), the longitudinal diffusion and solid–liquid mass transfer resistance reduced HETP terms were measured. The reduced short-range eddy dispersion HETP was taken from the literature data. The long-range reduced HETP was directly measured from the subtraction of these HETP terms to the overall HETP measured from moment analysis. In contrast to RPLC, the plots of the reduced HETP versus the reduced velocity depend weakly on the retention factor, due to the constant, low intra-particle diffusivity observed in HILIC. So, the reduced longitudinal diffusion HETP is smaller and the reduced solid–liquid mass transfer resistance HETP is larger in HILIC than in RPLC. Whereas border effects can be concealed in RPLC for retained analytes due to fast radial equilibration across the column diameter, a residual long-range eddy dispersion term persists in 4.6mm I.D. HILIC columns, even at very slow flow rates. Experiments show that the minor differences in the long-range eddy dispersion term between analytes having different retention factors is directly correlated to the reciprocal of their bulk diffusion coefficient. The performance of HILIC columns packed with fine particles is then more sensitive to the inlet sample distribution and to the outlet sample collection than RPLC columns due to the relatively poor radial mixing controlled by lateral diffusion.
A new metabolomic workflow for early detection of Alzheimer's disease
18 July 2013,
09:11:36
Publication date: 9 August
2013
Source:Journal of Chromatography A, Volume 1302
Author(s): Clara Ibáñez , Carolina Simó , Dinesh K. Barupal , Oliver Fiehn , Miia Kivipelto , Angel Cedazo-Mínguez , Alejandro Cifuentes
Alzheimer's disease (AD) is the most prevalent cause of dementia among older people. Although AD probably starts 20–30 years before first clinical symptoms become noticeable, nowadays it cannot be diagnosed accurately in its early stages. In this work, we present a new MS-based metabolomic approach based on the use of ultra-high performance liquid chromatography–time-of-flight mass spectrometry (UHPLC–TOF MS) to investigate cerebrospinal fluid (CSF) samples from patients with different AD stages. With the aim to obtain wide metabolome coverage two different chromatographic separation modes, namely reversed phase (RP) and hydrophilic interaction chromatography (HILIC), were used. RP/UHPLC–MS and HILIC/UHPLC–MS methods were optimized and applied to analyze CSF samples from 75 patients related to AD progression. Significant metabolic differences in CSF samples from subjects with different cognitive status related to AD progression were detected using this methodology, obtaining a group of potential biomarkers together with a classification model by means of a multivariate statistical analysis. The proposed model predicted the development of AD with an accuracy of 98.7% and specificity and sensitivity values above of 95%.
Source:Journal of Chromatography A, Volume 1302
Author(s): Clara Ibáñez , Carolina Simó , Dinesh K. Barupal , Oliver Fiehn , Miia Kivipelto , Angel Cedazo-Mínguez , Alejandro Cifuentes
Alzheimer's disease (AD) is the most prevalent cause of dementia among older people. Although AD probably starts 20–30 years before first clinical symptoms become noticeable, nowadays it cannot be diagnosed accurately in its early stages. In this work, we present a new MS-based metabolomic approach based on the use of ultra-high performance liquid chromatography–time-of-flight mass spectrometry (UHPLC–TOF MS) to investigate cerebrospinal fluid (CSF) samples from patients with different AD stages. With the aim to obtain wide metabolome coverage two different chromatographic separation modes, namely reversed phase (RP) and hydrophilic interaction chromatography (HILIC), were used. RP/UHPLC–MS and HILIC/UHPLC–MS methods were optimized and applied to analyze CSF samples from 75 patients related to AD progression. Significant metabolic differences in CSF samples from subjects with different cognitive status related to AD progression were detected using this methodology, obtaining a group of potential biomarkers together with a classification model by means of a multivariate statistical analysis. The proposed model predicted the development of AD with an accuracy of 98.7% and specificity and sensitivity values above of 95%.
Chromatographic background drift correction coupled with parallel factor analysis to resolve coelution problems in three-dimensional chromatographic data: Quantification of eleven antibiotics in tap water samples by high-performance liquid chromatography coupled with a diode array detector
18 July 2013,
09:11:36
Publication date: 9 August
2013
Source:Journal of Chromatography A, Volume 1302
Author(s): Yong-Jie Yu , Hai-Long Wu , Hai-Yan Fu , Juan Zhao , Yuan-Na Li , Shu-Fang Li , Chao Kang , Ru-Qin Yu
Chromatographic background drift correction has been an important field of research in chromatographic analysis. In the present work, orthogonal spectral space projection for background drift correction of three-dimensional chromatographic data was described in detail and combined with parallel factor analysis (PARAFAC) to resolve overlapped chromatographic peaks and obtain the second-order advantage. This strategy was verified by simulated chromatographic data and afforded significant improvement in quantitative results. Finally, this strategy was successfully utilized to quantify eleven antibiotics in tap water samples. Compared with the traditional methodology of introducing excessive factors for the PARAFAC model to eliminate the effect of background drift, clear improvement in the quantitative performance of PARAFAC was observed after background drift correction by orthogonal spectral space projection.
Source:Journal of Chromatography A, Volume 1302
Author(s): Yong-Jie Yu , Hai-Long Wu , Hai-Yan Fu , Juan Zhao , Yuan-Na Li , Shu-Fang Li , Chao Kang , Ru-Qin Yu
Chromatographic background drift correction has been an important field of research in chromatographic analysis. In the present work, orthogonal spectral space projection for background drift correction of three-dimensional chromatographic data was described in detail and combined with parallel factor analysis (PARAFAC) to resolve overlapped chromatographic peaks and obtain the second-order advantage. This strategy was verified by simulated chromatographic data and afforded significant improvement in quantitative results. Finally, this strategy was successfully utilized to quantify eleven antibiotics in tap water samples. Compared with the traditional methodology of introducing excessive factors for the PARAFAC model to eliminate the effect of background drift, clear improvement in the quantitative performance of PARAFAC was observed after background drift correction by orthogonal spectral space projection.
Preparation and chromatographic evaluation of a novel phosphate ester-bonded stationary phase with complexation and hydrophobic interactions retention mechanism
18 July 2013,
09:11:36
Publication date: 9 August
2013
Source:Journal of Chromatography A, Volume 1302
Author(s): Xiao-Dong Cheng , Xi-Tian Peng , Qiong-Wei Yu , Bi-Feng Yuan , Yu-Qi Feng
The present study described the preparation of a novel phosphate ester-bonded silica (PES) stationary phase based on “thiol-ene” click chemistry. The composition of the surface grafts of PES stationary phase was determined by elemental analysis and solid state 31P MAS NMR. Due to its hydrophilic phosphate-ester groups and short hydrophobic alkyl chains, the PES stationary phase exhibited dual retention mechanism via complexation and hydrophobic interactions with phenols. Benefiting from this special interaction mechanism, the newly synthesized PES stationary phase showed better selectivity in the separation of phenols compared to commercial octadecylsilyl-bonded silica (C18) columns. Furthermore, the separations of 10 nucleosides and nucleobases on the PES stationary phase were achieved in both reversed-phase liquid chromatography (RPLC) mode and hydrophilic interaction liquid chromatography (HILIC) mode.
Source:Journal of Chromatography A, Volume 1302
Author(s): Xiao-Dong Cheng , Xi-Tian Peng , Qiong-Wei Yu , Bi-Feng Yuan , Yu-Qi Feng
The present study described the preparation of a novel phosphate ester-bonded silica (PES) stationary phase based on “thiol-ene” click chemistry. The composition of the surface grafts of PES stationary phase was determined by elemental analysis and solid state 31P MAS NMR. Due to its hydrophilic phosphate-ester groups and short hydrophobic alkyl chains, the PES stationary phase exhibited dual retention mechanism via complexation and hydrophobic interactions with phenols. Benefiting from this special interaction mechanism, the newly synthesized PES stationary phase showed better selectivity in the separation of phenols compared to commercial octadecylsilyl-bonded silica (C18) columns. Furthermore, the separations of 10 nucleosides and nucleobases on the PES stationary phase were achieved in both reversed-phase liquid chromatography (RPLC) mode and hydrophilic interaction liquid chromatography (HILIC) mode.
Fast determination of perfluorocompounds in packaging by focused ultrasound solid–liquid extraction and liquid chromatography coupled to quadrupole-time of flight mass spectrometry
18 July 2013,
09:11:36
Publication date: 9 August
2013
Source:Journal of Chromatography A, Volume 1302
Author(s): Cristina Moreta , María Teresa Tena
A focused ultrasound solid–liquid extraction (FUSLE) and liquid chromatography (HPLC) coupled to quadrupole-time of flight mass spectrometry (QTOF-MS/MS) based method is proposed to determine six perfluorocarboxylic acids (PFCA) and perfluorooctane sulfonate (PFOS) in food-contact packaging. FUSLE, a simple, inexpensive and fast extraction technique, has been carried out with just 8mL of ethanol in one cycle of only 10s. The whole method presented good repeatability and intermediate precision, with RSDs below 11% and 15%, respectively; limits of detection, with values between 0.5ng/g and 2.2ng/g, and successful recovery values, around 100% in all cases. The developed method has been validated and applied to the analysis of real food-contact packaging samples. FUSLE results have been compared to those obtained with pressurized liquid extraction (PLE) and no significant differences between them have been found. PFAA were detected in all the packaging samples analyzed, in a concentration range between 4ng/g and 29ng/g, being PFHpA (perfluoroheptanoic acid) the most abundant of them.
Source:Journal of Chromatography A, Volume 1302
Author(s): Cristina Moreta , María Teresa Tena
A focused ultrasound solid–liquid extraction (FUSLE) and liquid chromatography (HPLC) coupled to quadrupole-time of flight mass spectrometry (QTOF-MS/MS) based method is proposed to determine six perfluorocarboxylic acids (PFCA) and perfluorooctane sulfonate (PFOS) in food-contact packaging. FUSLE, a simple, inexpensive and fast extraction technique, has been carried out with just 8mL of ethanol in one cycle of only 10s. The whole method presented good repeatability and intermediate precision, with RSDs below 11% and 15%, respectively; limits of detection, with values between 0.5ng/g and 2.2ng/g, and successful recovery values, around 100% in all cases. The developed method has been validated and applied to the analysis of real food-contact packaging samples. FUSLE results have been compared to those obtained with pressurized liquid extraction (PLE) and no significant differences between them have been found. PFAA were detected in all the packaging samples analyzed, in a concentration range between 4ng/g and 29ng/g, being PFHpA (perfluoroheptanoic acid) the most abundant of them.
Rapid screening of drugs of abuse in human urine by high-performance liquid chromatography coupled with high resolution and high mass accuracy hybrid linear ion trap-Orbitrap mass spectrometry
18 July 2013,
09:11:36
Publication date: 9 August
2013
Source:Journal of Chromatography A, Volume 1302
Author(s): Xiaowen Li , Baohua Shen , Zheng Jiang , Yi Huang , Xianyi Zhuo
A novel analytical toxicology method has been developed for the analysis of drugs of abuse in human urine by using a high resolution and high mass accuracy hybrid linear ion trap-Orbitrap mass spectrometer (LTQ-Orbitrap-MS). This method allows for the detection of different drugs of abuse, including amphetamines, cocaine, opiate alkaloids, cannabinoids, hallucinogens and their metabolites. After solid-phase extraction with Oasis HLB cartridges, spiked urine samples were analysed by HPLC/LTQ-Orbitrap-MS using an electrospray interface in positive ionisation mode, with resolving power of 30,000 full width at half maximum (FWHM). Gradient elution off of a Hypersil Gold PFP column (50mm×2.1mm) allowed to resolve 65 target compounds and 3 internal standards in a total chromatographic run time of 20min. Validation of this method consisted of confirmation of identity, selectivity, linearity, limit of detection (LOD), lowest limits of quantification (LLOQ), accuracy, precision, extraction recovery and matrix effect. The regression coefficients (r 2) for the calibration curves (LLOQ – 100ng/mL) in the study were ≥0.99. The LODs for 65 validated compounds were better than 5ng/ml except for 4 compounds. The relative standard deviation (RSD), which was used to estimate repeatability at three concentrations, was always less than 15%. The recovery of extraction and matrix effects were above 50 and 70%, respectively. Mass accuracy was always better than 2ppm, corresponding to a maximum mass error of 0.8 millimass units (mmu). The accurate masses of characteristic fragments were obtained by collisional experiments for a more reliable identification of the analytes. Automated data analysis and reporting were performed using ToxID software with an exact mass database. This procedure was then successfully applied to analyse drugs of abuse in a real urine sample from subject who was assumed to be drug addict.
Source:Journal of Chromatography A, Volume 1302
Author(s): Xiaowen Li , Baohua Shen , Zheng Jiang , Yi Huang , Xianyi Zhuo
A novel analytical toxicology method has been developed for the analysis of drugs of abuse in human urine by using a high resolution and high mass accuracy hybrid linear ion trap-Orbitrap mass spectrometer (LTQ-Orbitrap-MS). This method allows for the detection of different drugs of abuse, including amphetamines, cocaine, opiate alkaloids, cannabinoids, hallucinogens and their metabolites. After solid-phase extraction with Oasis HLB cartridges, spiked urine samples were analysed by HPLC/LTQ-Orbitrap-MS using an electrospray interface in positive ionisation mode, with resolving power of 30,000 full width at half maximum (FWHM). Gradient elution off of a Hypersil Gold PFP column (50mm×2.1mm) allowed to resolve 65 target compounds and 3 internal standards in a total chromatographic run time of 20min. Validation of this method consisted of confirmation of identity, selectivity, linearity, limit of detection (LOD), lowest limits of quantification (LLOQ), accuracy, precision, extraction recovery and matrix effect. The regression coefficients (r 2) for the calibration curves (LLOQ – 100ng/mL) in the study were ≥0.99. The LODs for 65 validated compounds were better than 5ng/ml except for 4 compounds. The relative standard deviation (RSD), which was used to estimate repeatability at three concentrations, was always less than 15%. The recovery of extraction and matrix effects were above 50 and 70%, respectively. Mass accuracy was always better than 2ppm, corresponding to a maximum mass error of 0.8 millimass units (mmu). The accurate masses of characteristic fragments were obtained by collisional experiments for a more reliable identification of the analytes. Automated data analysis and reporting were performed using ToxID software with an exact mass database. This procedure was then successfully applied to analyse drugs of abuse in a real urine sample from subject who was assumed to be drug addict.
Analysis of wax esters by silver-ion high-performance liquid chromatography–tandem mass spectrometry
18 July 2013,
09:11:36
Publication date: 9 August
2013
Source:Journal of Chromatography A, Volume 1302
Author(s): Vladimír Vrkoslav , Klára Urbanová , Matina Háková , Josef Cvačka
Wax esters (WEs), esters of long-chain fatty acids and long-chain alcohols, were analysed by Ag-HPLC/APCI-MS/MS. Two ChromSpher Lipids columns connected in series (a total length of 50cm) and hexane–2-propanol–acetonitrile mobile phases were used to achieve good separation of the molecular species. The chromatographic behaviour of WEs was studied under optimised conditions: retention increased with the number of double bonds and with the temperature (15–35°C); retention times were affected by the double-bond position, trans isomers eluted earlier than cis isomers, and the WEs were partially separated depending on the aliphatic-chain length. The WEs provided simple APCI spectra with [M+H]+ ions, the MS/MS spectra showed fragments, which allowed their identification. The method was applied for an analysis of the WE mixtures from jojoba oil and human hair and the results were compared with analogous data from an optimised RP-HPLC system.
Source:Journal of Chromatography A, Volume 1302
Author(s): Vladimír Vrkoslav , Klára Urbanová , Matina Háková , Josef Cvačka
Wax esters (WEs), esters of long-chain fatty acids and long-chain alcohols, were analysed by Ag-HPLC/APCI-MS/MS. Two ChromSpher Lipids columns connected in series (a total length of 50cm) and hexane–2-propanol–acetonitrile mobile phases were used to achieve good separation of the molecular species. The chromatographic behaviour of WEs was studied under optimised conditions: retention increased with the number of double bonds and with the temperature (15–35°C); retention times were affected by the double-bond position, trans isomers eluted earlier than cis isomers, and the WEs were partially separated depending on the aliphatic-chain length. The WEs provided simple APCI spectra with [M+H]+ ions, the MS/MS spectra showed fragments, which allowed their identification. The method was applied for an analysis of the WE mixtures from jojoba oil and human hair and the results were compared with analogous data from an optimised RP-HPLC system.
Measurement of activity coefficients of mixtures by head-space gas chromatography: General procedure
18 July 2013,
09:11:36
Publication date: 9 August
2013
Source:Journal of Chromatography A, Volume 1302
Author(s): Patricia Luis , Christine Wouters , Bart Van der Bruggen , Stanley I. Sandler
Head-space gas chromatography (HS-GC) is an applicable method to perform vapor–liquid equilibrium measurements and determine activity coefficients. However, the reproducibility of the data may be conditioned by the experimental procedure concerning to the automated pressure-balanced system. The study developed in this work shows that a minimum volume of liquid in the vial is necessary to ensure the reliability of the activity coefficients since it may become a parameter that influences the magnitude of the peak areas: the helium introduced during the pressurization step may produce significant variations of the results when too small volume of liquid is selected. The minimum volume required should thus be evaluated prior to obtain experimentally the concentration in the vapor phase and the activity coefficients. In this work, the mixture acetonitrile–toluene is taken as example, requiring a sample volume of more than 5mL (about more than 25% of the vial volume). The vapor–liquid equilibrium and activity coefficients of mixtures at different concentrations (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 molar fraction) and four temperatures (35, 45, 55 and 70°C) have been determined. Relative standard deviations (RSD) lower than 5% have been obtained, indicating the good reproducibility of the method when a sample volume larger than 5mL is used. Finally, a general procedure to measure activity coefficients by means of pressure-balanced head-space gas chromatography is proposed.
Source:Journal of Chromatography A, Volume 1302
Author(s): Patricia Luis , Christine Wouters , Bart Van der Bruggen , Stanley I. Sandler
Head-space gas chromatography (HS-GC) is an applicable method to perform vapor–liquid equilibrium measurements and determine activity coefficients. However, the reproducibility of the data may be conditioned by the experimental procedure concerning to the automated pressure-balanced system. The study developed in this work shows that a minimum volume of liquid in the vial is necessary to ensure the reliability of the activity coefficients since it may become a parameter that influences the magnitude of the peak areas: the helium introduced during the pressurization step may produce significant variations of the results when too small volume of liquid is selected. The minimum volume required should thus be evaluated prior to obtain experimentally the concentration in the vapor phase and the activity coefficients. In this work, the mixture acetonitrile–toluene is taken as example, requiring a sample volume of more than 5mL (about more than 25% of the vial volume). The vapor–liquid equilibrium and activity coefficients of mixtures at different concentrations (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 molar fraction) and four temperatures (35, 45, 55 and 70°C) have been determined. Relative standard deviations (RSD) lower than 5% have been obtained, indicating the good reproducibility of the method when a sample volume larger than 5mL is used. Finally, a general procedure to measure activity coefficients by means of pressure-balanced head-space gas chromatography is proposed.
No comments:
Post a Comment