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Selected papers from the latest issue:
C12-Ag wire as solid-phase microextraction fiber for determination of benzophenone ultraviolet filters in river water
17 June 2013,
14:44:09
Publication date: 12 July
2013
Source:Journal of Chromatography A, Volume 1298
Author(s): Jian Li , Liyun Ma , Minqiong Tang , Li Xu
In the present study, a novel approach for fabrication of solid-phase microextraction (SPME) fiber based on silver wire was proposed. 3-(Mercaptopropyl) trimethoxysilane (MPTS) was self-assembled on the silver wire by the special interaction between Ag and S, producing MPTS-Ag wire. The MPTS-Ag wire was then functionalized with dodecyltrimethoxysilane via sol–gel approach, giving C12-Ag wire. The preparation conditions were systematically optimized. The prepared fiber was then used as the SPME fiber to extract three benzophenone UV filters from the river water. The developed method showed good linearity between 0.005 and 0.200μgmL−1 with regression determination coefficients in the range of 0.9929–0.9988 and detection limits ranging from 0.58 to 1.86ngmL−1. The C12-Ag fiber exhibited good stability and long lifetime, and could be an alternative to the traditional fused silica fiber.
Source:Journal of Chromatography A, Volume 1298
Author(s): Jian Li , Liyun Ma , Minqiong Tang , Li Xu
In the present study, a novel approach for fabrication of solid-phase microextraction (SPME) fiber based on silver wire was proposed. 3-(Mercaptopropyl) trimethoxysilane (MPTS) was self-assembled on the silver wire by the special interaction between Ag and S, producing MPTS-Ag wire. The MPTS-Ag wire was then functionalized with dodecyltrimethoxysilane via sol–gel approach, giving C12-Ag wire. The preparation conditions were systematically optimized. The prepared fiber was then used as the SPME fiber to extract three benzophenone UV filters from the river water. The developed method showed good linearity between 0.005 and 0.200μgmL−1 with regression determination coefficients in the range of 0.9929–0.9988 and detection limits ranging from 0.58 to 1.86ngmL−1. The C12-Ag fiber exhibited good stability and long lifetime, and could be an alternative to the traditional fused silica fiber.
Simultaneous extraction of metabolome and lipidome with methyl tert-butyl ether from a single small tissue sample for ultra-high performance liquid chromatography/mass spectrometry
17 June 2013,
14:44:09
Publication date: 12 July
2013
Source:Journal of Chromatography A, Volume 1298
Author(s): Shili Chen , Miriam Hoene , Jia Li , Yanjie Li , Xinjie Zhao , Hans-Ulrich Häring , Erwin D. Schleicher , Cora Weigert , Guowang Xu , Rainer Lehmann
A common challenge for scientists working with animal tissue or human biopsy samples is the limitation of material and consequently, the difficulty to perform comprehensive metabolic profiling within one experiment. Here, we present a novel approach to simultaneously perform targeted and non-targeted metabolomics as well as lipidomics from one small piece of liver or muscle tissue by ultra-high performance liquid chromatography/mass spectrometry (UHPLC/MS) following a methyl tert-butyl ether (MTBE)-based extraction. Equal relative amounts of the resulting polar and non-polar fractions were pooled, evaporated and reconstituted in the appropriate solvent for UHPLC/MS analysis. This mix was comparable or superior in yield and reproducibility to a standard 80% methanol extraction for the profiling of polar and lipophilic metabolites (free carnitine, acylcarnitines and FFA). The mix was also suitable for non-targeted metabolomics, an easy measure to increase the metabolite coverage by 30% relative to using the polar fraction alone. Lipidomics was performed from an aliquot of the non-polar fraction. This novel strategy could successfully be applied to one mouse soleus muscle with a dry weight of merely 2.5mg. By enabling a simultaneous profiling of lipids and metabolites with mixed polarity while saving material for molecular, biochemical or histological analyses, our approach may open up new perspectives toward a comprehensive investigation of small, valuable tissue samples.
Source:Journal of Chromatography A, Volume 1298
Author(s): Shili Chen , Miriam Hoene , Jia Li , Yanjie Li , Xinjie Zhao , Hans-Ulrich Häring , Erwin D. Schleicher , Cora Weigert , Guowang Xu , Rainer Lehmann
A common challenge for scientists working with animal tissue or human biopsy samples is the limitation of material and consequently, the difficulty to perform comprehensive metabolic profiling within one experiment. Here, we present a novel approach to simultaneously perform targeted and non-targeted metabolomics as well as lipidomics from one small piece of liver or muscle tissue by ultra-high performance liquid chromatography/mass spectrometry (UHPLC/MS) following a methyl tert-butyl ether (MTBE)-based extraction. Equal relative amounts of the resulting polar and non-polar fractions were pooled, evaporated and reconstituted in the appropriate solvent for UHPLC/MS analysis. This mix was comparable or superior in yield and reproducibility to a standard 80% methanol extraction for the profiling of polar and lipophilic metabolites (free carnitine, acylcarnitines and FFA). The mix was also suitable for non-targeted metabolomics, an easy measure to increase the metabolite coverage by 30% relative to using the polar fraction alone. Lipidomics was performed from an aliquot of the non-polar fraction. This novel strategy could successfully be applied to one mouse soleus muscle with a dry weight of merely 2.5mg. By enabling a simultaneous profiling of lipids and metabolites with mixed polarity while saving material for molecular, biochemical or histological analyses, our approach may open up new perspectives toward a comprehensive investigation of small, valuable tissue samples.
Model-based prediction of monoclonal antibody retention in ion-exchange chromatography
17 June 2013,
14:44:09
Publication date: 12 July
2013
Source:Journal of Chromatography A, Volume 1298
Author(s): Bertrand Guélat , Lydia Delegrange , Pascal Valax , Massimo Morbidelli
In order to support a model-based process design in ion-exchange chromatography, an adsorption equilibrium model was adapted to predict the protein retention behavior from the amino acid sequence and from structural information on the resin. It is based on the computation of protein–resin interactions with a colloidal model and accounts for the contribution of each ionizable amino acid to the protein charge. As a verification of the protein charge model, the experimental titration curve of a monoclonal antibody was compared to its predicted net charge. Using this protein charge model in the computation of the protein–resin interactions, it is possible to predict the adsorption equilibrium constant (i.e. retention factor or Henry constant) with an explicit pH and salt dependence. The application of the model-based predictions for an in silico screening of the protein retention on various stationary phases or, alternatively, for the comparison of various monoclonal antibodies on a given cation-exchanger was demonstrated. Furthermore, considering the structural differences between charge variants of a monoclonal antibody, it was possible to predict their individual retention times. The selectivity between the side variants and the main isoform of the monoclonal antibody were computed. The comparison with the experimental data showed that the model was reliable with respect to the identification of the operating conditions maximizing the selectivity, i.e. the most promising conditions for a monoclonal antibody variant separation. Such predictions can be useful in reducing the experimental effort to identify the parameter space.
Source:Journal of Chromatography A, Volume 1298
Author(s): Bertrand Guélat , Lydia Delegrange , Pascal Valax , Massimo Morbidelli
In order to support a model-based process design in ion-exchange chromatography, an adsorption equilibrium model was adapted to predict the protein retention behavior from the amino acid sequence and from structural information on the resin. It is based on the computation of protein–resin interactions with a colloidal model and accounts for the contribution of each ionizable amino acid to the protein charge. As a verification of the protein charge model, the experimental titration curve of a monoclonal antibody was compared to its predicted net charge. Using this protein charge model in the computation of the protein–resin interactions, it is possible to predict the adsorption equilibrium constant (i.e. retention factor or Henry constant) with an explicit pH and salt dependence. The application of the model-based predictions for an in silico screening of the protein retention on various stationary phases or, alternatively, for the comparison of various monoclonal antibodies on a given cation-exchanger was demonstrated. Furthermore, considering the structural differences between charge variants of a monoclonal antibody, it was possible to predict their individual retention times. The selectivity between the side variants and the main isoform of the monoclonal antibody were computed. The comparison with the experimental data showed that the model was reliable with respect to the identification of the operating conditions maximizing the selectivity, i.e. the most promising conditions for a monoclonal antibody variant separation. Such predictions can be useful in reducing the experimental effort to identify the parameter space.
Distributed pore model for bio-molecule chromatography
17 June 2013,
14:44:09
Publication date: 12 July
2013
Source:Journal of Chromatography A, Volume 1298
Author(s): Bertrand Coquebert de Neuville , Abhijit Tarafder , Massimo Morbidelli
One of the main peculiarities in protein chromatography is that the adsorbing proteins and the adsorbent pores have comparable sizes. This has the consequence that the pore accessibility depends not only on the solute size but also on the loading conditions of the adsorbent because protein adsorption significantly reduces the size of the pores. A model that accounts for the pore size distribution of the stationary phase and for the pore shrinkage due to protein adsorption has been developed to describe mass transport and adsorption in the porous particles. This model has been shown to be equivalent to the general rate model (GRM) in the case of processes under highly diluted conditions with little adsorption. This implies that the model parameters determination follows the same procedure as for the classical GRM. The new pore model has been applied and compared to the GRM for the simulation of lysozyme breakthrough experiments and for the prediction of 5% dynamic binding capacity values solely based on static capacity measurements.
Source:Journal of Chromatography A, Volume 1298
Author(s): Bertrand Coquebert de Neuville , Abhijit Tarafder , Massimo Morbidelli
One of the main peculiarities in protein chromatography is that the adsorbing proteins and the adsorbent pores have comparable sizes. This has the consequence that the pore accessibility depends not only on the solute size but also on the loading conditions of the adsorbent because protein adsorption significantly reduces the size of the pores. A model that accounts for the pore size distribution of the stationary phase and for the pore shrinkage due to protein adsorption has been developed to describe mass transport and adsorption in the porous particles. This model has been shown to be equivalent to the general rate model (GRM) in the case of processes under highly diluted conditions with little adsorption. This implies that the model parameters determination follows the same procedure as for the classical GRM. The new pore model has been applied and compared to the GRM for the simulation of lysozyme breakthrough experiments and for the prediction of 5% dynamic binding capacity values solely based on static capacity measurements.
Preparation and evaluation of 1,6-hexanediol ethoxylate diacrylate-based alkyl methacrylate monolithic capillary column for separating small molecules
17 June 2013,
14:44:09
Publication date: 12 July
2013
Source:Journal of Chromatography A, Volume 1298
Author(s): Shu-Ling Lin , Yu-Ru Wu , Tzuen-Yeuan Lin , Ming-Ren Fuh
Due to the high porosity, good thermal stability, and good physical stability at high pressure, polymer monoliths have been successfully utilized as the stationary phases for capillary liquid chromatography (LC) analysis. In this study, we introduced 1,6-hexanediol ethoxylate diacrylate (HEDA) as a cross-linker to prepare alkyl methacrylate monoliths for efficient separation of polar small molecules. HEDA provided additional dipole–dipole interactions between the monolithic stationary phases and polar analytes. For comparison, ethylene dimethacrylate and 1,6-hexanediol dimethacrylate were also utilized as cross-linkers to prepare alkyl methacrylate monoliths. A series of alkyl methacrylate polymeric monoliths were synthesized in fused-silica capillaries using the three different cross-linkers. The porosity, permeability and column efficiency of the synthesized alkyl methacrylate monoliths were characterized. A mixture of phenol derivatives was employed to evaluate the applicability of the prepared monolithic columns for separating small molecules using capillary LC. The HEDA-based alkyl methacrylate monoliths offered the most efficient chromatographic separation for phenol derivatives. Moreover, the capability of applying the novel HEDA-based alkyl methacrylate monolithic columns for potential environmental analysis was demonstrated by separating eight phenylurea herbicides.
Source:Journal of Chromatography A, Volume 1298
Author(s): Shu-Ling Lin , Yu-Ru Wu , Tzuen-Yeuan Lin , Ming-Ren Fuh
Due to the high porosity, good thermal stability, and good physical stability at high pressure, polymer monoliths have been successfully utilized as the stationary phases for capillary liquid chromatography (LC) analysis. In this study, we introduced 1,6-hexanediol ethoxylate diacrylate (HEDA) as a cross-linker to prepare alkyl methacrylate monoliths for efficient separation of polar small molecules. HEDA provided additional dipole–dipole interactions between the monolithic stationary phases and polar analytes. For comparison, ethylene dimethacrylate and 1,6-hexanediol dimethacrylate were also utilized as cross-linkers to prepare alkyl methacrylate monoliths. A series of alkyl methacrylate polymeric monoliths were synthesized in fused-silica capillaries using the three different cross-linkers. The porosity, permeability and column efficiency of the synthesized alkyl methacrylate monoliths were characterized. A mixture of phenol derivatives was employed to evaluate the applicability of the prepared monolithic columns for separating small molecules using capillary LC. The HEDA-based alkyl methacrylate monoliths offered the most efficient chromatographic separation for phenol derivatives. Moreover, the capability of applying the novel HEDA-based alkyl methacrylate monolithic columns for potential environmental analysis was demonstrated by separating eight phenylurea herbicides.
Analysis of immobilized artificial membrane retention factors for both neutral and ionic species
17 June 2013,
14:44:09
Publication date: 12 July
2013
Source:Journal of Chromatography A, Volume 1298
Author(s): Michael H. Abraham , William E. Acree Jr. , Alfred Fahr , Xiangli Liu
Retention data on an immobilised artificial membrane have been taken from the work of Li et al. and from Liu et al., and have been correlated with a set of descriptors that includes descriptors for ionized species, that is anions from deprotonated acids and cations from protonated bases. Log k(IAM) values can be predicted for acids or bases that are partially ionized at the experimental pH and log k(IAM) values for acids and bases can be predicted as a function of the fraction present as the ionized species, equivalent to prediction as a function of pH. It is shown that anions reduce the value of log k(IAM) by about 1.1log units but that cations have almost no effect by comparison to the neutral species. By comparison to non-polar solvents, carboxylate anions and protonated base cations are considerably stabilized by both water and the IAM phase to about 6–8log units and so the rather small influence of anions (−1.1log unit) and cations (−0.1log unit) on log k(IAM) is due to substantial cancellation of these stabilization effects. Indeed, the effect of change of phase from water to IAM on the neutral species is at least as large as the effect of change of phase on the ionic species.
Source:Journal of Chromatography A, Volume 1298
Author(s): Michael H. Abraham , William E. Acree Jr. , Alfred Fahr , Xiangli Liu
Retention data on an immobilised artificial membrane have been taken from the work of Li et al. and from Liu et al., and have been correlated with a set of descriptors that includes descriptors for ionized species, that is anions from deprotonated acids and cations from protonated bases. Log k(IAM) values can be predicted for acids or bases that are partially ionized at the experimental pH and log k(IAM) values for acids and bases can be predicted as a function of the fraction present as the ionized species, equivalent to prediction as a function of pH. It is shown that anions reduce the value of log k(IAM) by about 1.1log units but that cations have almost no effect by comparison to the neutral species. By comparison to non-polar solvents, carboxylate anions and protonated base cations are considerably stabilized by both water and the IAM phase to about 6–8log units and so the rather small influence of anions (−1.1log unit) and cations (−0.1log unit) on log k(IAM) is due to substantial cancellation of these stabilization effects. Indeed, the effect of change of phase from water to IAM on the neutral species is at least as large as the effect of change of phase on the ionic species.
Direct quantification of bacterial molybdenum and iron metallophores with ultra-high-performance liquid chromatography coupled to time-of-flight mass spectrometry
17 June 2013,
14:44:09
Publication date: 12 July
2013
Source:Journal of Chromatography A, Volume 1298
Author(s): Michael Deicke , Jean-Philippe Bellenger , Thomas Wichard
Metallophores are a unique class of organic ligands released, for example, by nitrogen fixing bacteria in their environment in order to recruit the micronutrients molybdenum (Mo) and iron (Fe). Mo and Fe are essential cofactors of nitrogenase that reduces atmospheric nitrogen into bioavailable ammonium. Upon release, these bacterial metallophores bind to both metal cations and oxo-anions in the extracellular medium increasing the bioavailability of the metals to the nitrogen fixers, which can subsequently recruit the complexes. The efficient quantification of those metal complexes is crucial for the understanding of the homeostasis of the metal cofactors of nitrogenase (e.g., Fe and Mo), the dynamics of nitrogen fixation and the nitrogen cycle. A novel direct ultra-high-performance liquid chromatography coupled to a time-of-flight mass spectrometer (UHPLC-ToF-MS) was developed to quantify and monitor the production of Fe and Mo complexes of the catecholate metallophores protochelin (Prot) and azotochelin (Azo) in the growth medium of the nitrogen fixer and model organism Azotobacter vinelandii. Chromatographic separations were carried on a reversed C18-phase with a mobile phase ramped from water to acetonitrile spiked with 1mmol/L ammonium acetate (pH 6.6) to achieve stability of the metal complexes. Linearity for Mo-protochelin and Fe-protochelin was found at the concentration range between 5.0×10−8 and 9.0×10−7 mol/L with a limit of detection of 2.0×10−8 and 3.0×10−8 mol/L, respectively. The coefficient of variation of the procedure is in the range from 1.5 to 3.4%. The validation has hence demonstrated that the UHPLC-ToF-MS methodology is a fast, precise, specific, robust, and sensitive approach allowing the direct measurement of metallophores in growth medium without any sample preparation. The UHPLC-ToF-MS methodology was applied to the analysis of metallophores in our laboratory. Under lower Mo concentration, the Mo-protochelin concentration peaks in the middle lag phase, while the Fe-protochelin concentration rises to two maxima at the beginning of the exponential phase and during the stationary phase. The results indicate that the production of metallophores is highly dynamic throughout the growth and has to be monitored with high sensitivity and temporal resolution.
Source:Journal of Chromatography A, Volume 1298
Author(s): Michael Deicke , Jean-Philippe Bellenger , Thomas Wichard
Metallophores are a unique class of organic ligands released, for example, by nitrogen fixing bacteria in their environment in order to recruit the micronutrients molybdenum (Mo) and iron (Fe). Mo and Fe are essential cofactors of nitrogenase that reduces atmospheric nitrogen into bioavailable ammonium. Upon release, these bacterial metallophores bind to both metal cations and oxo-anions in the extracellular medium increasing the bioavailability of the metals to the nitrogen fixers, which can subsequently recruit the complexes. The efficient quantification of those metal complexes is crucial for the understanding of the homeostasis of the metal cofactors of nitrogenase (e.g., Fe and Mo), the dynamics of nitrogen fixation and the nitrogen cycle. A novel direct ultra-high-performance liquid chromatography coupled to a time-of-flight mass spectrometer (UHPLC-ToF-MS) was developed to quantify and monitor the production of Fe and Mo complexes of the catecholate metallophores protochelin (Prot) and azotochelin (Azo) in the growth medium of the nitrogen fixer and model organism Azotobacter vinelandii. Chromatographic separations were carried on a reversed C18-phase with a mobile phase ramped from water to acetonitrile spiked with 1mmol/L ammonium acetate (pH 6.6) to achieve stability of the metal complexes. Linearity for Mo-protochelin and Fe-protochelin was found at the concentration range between 5.0×10−8 and 9.0×10−7 mol/L with a limit of detection of 2.0×10−8 and 3.0×10−8 mol/L, respectively. The coefficient of variation of the procedure is in the range from 1.5 to 3.4%. The validation has hence demonstrated that the UHPLC-ToF-MS methodology is a fast, precise, specific, robust, and sensitive approach allowing the direct measurement of metallophores in growth medium without any sample preparation. The UHPLC-ToF-MS methodology was applied to the analysis of metallophores in our laboratory. Under lower Mo concentration, the Mo-protochelin concentration peaks in the middle lag phase, while the Fe-protochelin concentration rises to two maxima at the beginning of the exponential phase and during the stationary phase. The results indicate that the production of metallophores is highly dynamic throughout the growth and has to be monitored with high sensitivity and temporal resolution.
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