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Selected papers from the latest issue:
Development and application of chiral crown ethers as selectors for chiral separation in high-performance liquid chromatography and nuclear magnetic resonance spectroscopy
14 January 2013,
01:18:17
25 January 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
Chiral crown ethers have been widely used in the resolution of various chiral compounds containing a primary amino group. Covalently bonded chiral stationary phases derived from (18-crown-6)-2,3,11,12-tetracarboxylic acid (18-C-6-TA) were developed in our groups and utilized for the resolution for several types of analytes. By use of NMR spectroscopy, chiral discrimination studies were performed for α-amino acids and their esters using 18-C-6-TA. Here, advances in the development and application of chiral stationary phases and chiral solvating agents using 18-C-6-TA for enantiomer resolution are described in relationship to recent chiral recognition mechanism studies.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
Chiral crown ethers have been widely used in the resolution of various chiral compounds containing a primary amino group. Covalently bonded chiral stationary phases derived from (18-crown-6)-2,3,11,12-tetracarboxylic acid (18-C-6-TA) were developed in our groups and utilized for the resolution for several types of analytes. By use of NMR spectroscopy, chiral discrimination studies were performed for α-amino acids and their esters using 18-C-6-TA. Here, advances in the development and application of chiral stationary phases and chiral solvating agents using 18-C-6-TA for enantiomer resolution are described in relationship to recent chiral recognition mechanism studies.
Highlights
► 18-C-6-TA was found to be one of the most effective chiral selectors. ► Advances in the application of using 18-C-6-TA is described. ► (+)- and (−)-CSP 1 based on 18-C-6-TA has been successfully commercialized.Cryogelation of molecularly imprinted nanoparticles: A macroporous structure as affinity chromatography column for removal of β-blockers from complex samples
14 January 2013,
01:18:17
25 January 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
In this work, a new macroporous molecularly imprinted cryogel (MIP composite cryogel) was synthesized by glutaraldehyde cross-linking reaction of poly(vinyl alcohol) (PVA) particles and amino-modified molecularly imprinted core–shell nanoparticles. The MIP core–shell nanoparticles were prepared using propranolol as a template by one-pot precipitation polymerization with sequential monomer addition. The characteristics of the MIP composite cryogel were studied by scanning electron microscopy (SEM) and texture analyzer. The macroporous structure of the composite (with the pore size varying from a few micrometers to 100μm) enabled high mass transfer of particulate-containing fluids. In a solid phase extraction (SPE) process, the efficiency and selectivity of the MIP composite cryogel were investigated, where the cryogel was used as an affinity matrix to remove propranolol from aqueous solution as well as from complex plasma sample without prior protein precipitation. The MIP composite cryogel maintained high selectivity and stability and could be used repeatedly after regeneration.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
In this work, a new macroporous molecularly imprinted cryogel (MIP composite cryogel) was synthesized by glutaraldehyde cross-linking reaction of poly(vinyl alcohol) (PVA) particles and amino-modified molecularly imprinted core–shell nanoparticles. The MIP core–shell nanoparticles were prepared using propranolol as a template by one-pot precipitation polymerization with sequential monomer addition. The characteristics of the MIP composite cryogel were studied by scanning electron microscopy (SEM) and texture analyzer. The macroporous structure of the composite (with the pore size varying from a few micrometers to 100μm) enabled high mass transfer of particulate-containing fluids. In a solid phase extraction (SPE) process, the efficiency and selectivity of the MIP composite cryogel were investigated, where the cryogel was used as an affinity matrix to remove propranolol from aqueous solution as well as from complex plasma sample without prior protein precipitation. The MIP composite cryogel maintained high selectivity and stability and could be used repeatedly after regeneration.
Highlights
► Preparation of composite cryogel with amino-modified MIP nanoparticles. ► Unique combination of high selectivity and highly porous interconnected structure. ► Stationary phase as affinity matrix for separation of targets from complex media. ► New solid phase extraction adsorbent for efficient removal of β-blockers.Computational and experimental investigation of molecular imprinted polymers for selective extraction of dimethoate and its metabolite omethoate from olive oil
14 January 2013,
01:18:17
25 January 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
This work presents the development of molecularly imprinted polymers (MIPs) for the selective extraction of dimethoate from olive oil. Computational simulations allowed selecting itaconic acid as the monomer showing the highest affinity towards dimethoate. Experimental validation confirmed modelling predictions and showed that the polymer based on IA as functional monomer and omethoate as template molecule displays the highest selectivity for the structurally similar pesticides dimethoate, omethoate and monocrotophos. Molecularly imprinted solid phase extraction (MISPE) method was developed and applied to the clean-up of olive oil extracts. It was found that the most suitable solvents for loading, washing and elution step were respectively hexane, hexane-dichloromethane (85:15%) and methanol. The developed MIPSE was successfully applied to extraction of dimethoate from olive oil, with recovery rates up to 94%. The limits of detection and quantification of the described method were respectively 0.012 and 0.05μgg−1.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
This work presents the development of molecularly imprinted polymers (MIPs) for the selective extraction of dimethoate from olive oil. Computational simulations allowed selecting itaconic acid as the monomer showing the highest affinity towards dimethoate. Experimental validation confirmed modelling predictions and showed that the polymer based on IA as functional monomer and omethoate as template molecule displays the highest selectivity for the structurally similar pesticides dimethoate, omethoate and monocrotophos. Molecularly imprinted solid phase extraction (MISPE) method was developed and applied to the clean-up of olive oil extracts. It was found that the most suitable solvents for loading, washing and elution step were respectively hexane, hexane-dichloromethane (85:15%) and methanol. The developed MIPSE was successfully applied to extraction of dimethoate from olive oil, with recovery rates up to 94%. The limits of detection and quantification of the described method were respectively 0.012 and 0.05μgg−1.
Highlights
► Development of molecular imprinted polymer (MIP), based on molecular modelling for dimethoate and its metabolite omethoate. ► Optimization of protocol molecularly imprinted solid phase extraction (MISPE). ► Application of the optimized protocol for extraction from real sample (olive oil). ► Validation of the developed system of extraction by comparison with extraction using conventional methods (C18 column).Quantitative multi-residue method for determination antibiotics in chicken meat using turbulent flow chromatography coupled to liquid chromatography–tandem mass spectrometry
14 January 2013,
01:18:17
25 January 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
A multi-class method for identification and quantification of 36 antibiotics from seven different chemical classes (aminoglycosides, macrolides, lincosamides, sulfonamides, tetracyclines, quinolones and trimethoprim) has been developed by using liquid chromatography–mass spectrometry. The method was optimised for detection of antibiotics in chicken meat. Sample preparation including extraction with a mixture of acetonitrile:2% trichloroacetic acid (45:55, v/v), centrifugation and filtration was followed by on-line clean-up using turbulent flow chromatography. Using this automated on-line technique enabled a larger number of samples to be analysed per day than with a traditional clean-up technique (e.g. solid phase extraction). The optimised method was validated according to the European Commission Directive 2002/657/EC. In-house validation was performed by fortifying the blank matrix at three levels 0.5, 1.0 and 1.5 MRL (maximum residue limit), or respectively, at concentrations as low as possible for substances without an MRL. Precision in terms of repeatability standard deviation ranged from 3 to 28% and recovery values were between 80 and 120% in most cases. All calculated validation parameters including CCα and CCβ were in the compliance with the legislative requirements.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
A multi-class method for identification and quantification of 36 antibiotics from seven different chemical classes (aminoglycosides, macrolides, lincosamides, sulfonamides, tetracyclines, quinolones and trimethoprim) has been developed by using liquid chromatography–mass spectrometry. The method was optimised for detection of antibiotics in chicken meat. Sample preparation including extraction with a mixture of acetonitrile:2% trichloroacetic acid (45:55, v/v), centrifugation and filtration was followed by on-line clean-up using turbulent flow chromatography. Using this automated on-line technique enabled a larger number of samples to be analysed per day than with a traditional clean-up technique (e.g. solid phase extraction). The optimised method was validated according to the European Commission Directive 2002/657/EC. In-house validation was performed by fortifying the blank matrix at three levels 0.5, 1.0 and 1.5 MRL (maximum residue limit), or respectively, at concentrations as low as possible for substances without an MRL. Precision in terms of repeatability standard deviation ranged from 3 to 28% and recovery values were between 80 and 120% in most cases. All calculated validation parameters including CCα and CCβ were in the compliance with the legislative requirements.
Highlights
► Multi-residue LC–MS/MS method for 7 different classes of antibiotics in chicken meat. ► Method validated according to the EU Commission Decision 2002/657/EC. ► On-line sample clean-up using turbo flow technology was employed. ► Significant reduction in sample treatment time compared to conventional methods.Low-density solvent-based vortex-assisted surfactant-enhanced-emulsification liquid–liquid microextraction combined with gas chromatography–mass spectrometry for the fast determination of phthalate esters in bottled water
14 January 2013,
01:18:17
25 January 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
For the first time, a novel low-density solvent-based vortex-assisted surfactant-enhanced-emulsification liquid–liquid microextraction (LDS–VSLLME) was developed for the fast, simple and efficient determination of six phthalate esters (PEs) in bottled water samples followed by gas chromatography–mass spectrometry (GC–MS). In the extraction procedure, the aqueous sample solution was injected into a mixture of extraction solvent (toluene) and surfactant (cetyltrimethyl ammonium bromide), which were placed in a glass tube with conical bottom, to form an emulsion by the assistance of vortex agitation. After extraction and phase separation by centrifugation, and removal of the spent sample, the toluene extract was collected and analyzed by GC–MS. The addition of surfactant enhanced the dispersion of extraction solvent in aqueous sample and was also favorable for the mass transfer of the analytes from the aqueous sample to the extraction solvent. Moreover, using a relatively less toxic surfactant as the emulsifier agent overcame the disadvantages of traditional organic dispersive solvents that are usually highly toxic and expensive and might conceivably decrease extraction efficiency to some extent since they are not as effective as surfactants themselves in generating an emulsion. With the aid of surfactant and vortex agitation to achieve good organic extraction solvent dispersion, extraction equilibrium was achieved within 1min, indicating it was a fast sample preparation technique. Another prominent feature of the method was the simple procedure to collect a less dense than water solvent by a microsyringe. After extraction and phase separation, the aqueous sample was removed using a 5-mL syringe, thus leaving behind the extract, which was retrieved easily. This novel method simplifies the use of low-density solvents in DLLME. Under the optimized conditions, the proposed method provided good linearity in the range of 0.05–25μg/L, low limits of detection (8–25ng/L) and good enrichment factors up to 290. The proposed method was successfully applied to the extraction of PEs in bottled water samples as a fast, efficient, and convenient method.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
For the first time, a novel low-density solvent-based vortex-assisted surfactant-enhanced-emulsification liquid–liquid microextraction (LDS–VSLLME) was developed for the fast, simple and efficient determination of six phthalate esters (PEs) in bottled water samples followed by gas chromatography–mass spectrometry (GC–MS). In the extraction procedure, the aqueous sample solution was injected into a mixture of extraction solvent (toluene) and surfactant (cetyltrimethyl ammonium bromide), which were placed in a glass tube with conical bottom, to form an emulsion by the assistance of vortex agitation. After extraction and phase separation by centrifugation, and removal of the spent sample, the toluene extract was collected and analyzed by GC–MS. The addition of surfactant enhanced the dispersion of extraction solvent in aqueous sample and was also favorable for the mass transfer of the analytes from the aqueous sample to the extraction solvent. Moreover, using a relatively less toxic surfactant as the emulsifier agent overcame the disadvantages of traditional organic dispersive solvents that are usually highly toxic and expensive and might conceivably decrease extraction efficiency to some extent since they are not as effective as surfactants themselves in generating an emulsion. With the aid of surfactant and vortex agitation to achieve good organic extraction solvent dispersion, extraction equilibrium was achieved within 1min, indicating it was a fast sample preparation technique. Another prominent feature of the method was the simple procedure to collect a less dense than water solvent by a microsyringe. After extraction and phase separation, the aqueous sample was removed using a 5-mL syringe, thus leaving behind the extract, which was retrieved easily. This novel method simplifies the use of low-density solvents in DLLME. Under the optimized conditions, the proposed method provided good linearity in the range of 0.05–25μg/L, low limits of detection (8–25ng/L) and good enrichment factors up to 290. The proposed method was successfully applied to the extraction of PEs in bottled water samples as a fast, efficient, and convenient method.
Highlights
► LDS–VSLLME–GC–MS was applied to the determination of PEs. ► Low density and less toxic organic solvent toluene was used as extractant. ► Good extraction solvent dispersion was achieved by relatively less toxic surfactant combined with vortex agitation. ► Fast extraction time (within 1min) and high extraction efficiency with good enrichment factors up to 290 were achieved. ► The low-density organic solvent collection procedure was simple and fast.Sample pretreatment optimization for the analysis of short chain chlorinated paraffins in soil with gas chromatography–electron capture negative ion-mass spectrometry
14 January 2013,
01:18:17
25 January 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
Accurately quantifying short chain chlorinated paraffins (SCCPs) in soil samples with gas chromatograph coupled with electron capture negative ionization mass spectrometry (GC–ECNI-MS) is difficult because many other polychlorinated pollutants are present in the sample matrices. These pollutants (e.g., polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and toxaphene) can cause serious interferences during SCCPs analysis with GC–MS. Four main columns packed with different adsorbents, including silica gel, Florisil and alumina, were investigated in this study to determine their performance for separating interfering pollutants from SCCPs. These experimental results suggest that the optimum cleanup procedure uses a silica gel column and a multilayer silica gel–Florisil composite column. This procedure completely separated 22 PCB congeners, 23 OCPs and three toxaphene congeners from SCCPs. However, p,p′-DDD, cis-nonachlor and o,p′-DDD were not completely removed and only 53% of the total toxaphene was removed. This optimized method was successfully and effectively applied for removing interfering pollutants from real soil samples. SCCPs in 17 soil samples from different land use areas within a suburban region were analyzed with the established method. The concentrations of SCCPs in these samples were between 7 and 541ngg−1 (mean: 84ngg−1). Similar homologue SCCPs patterns were observed between the soil samples collected from different land use areas. In addition, lower chlorinated (Cl6/7) C10- and C11- SCCPs were the dominant congeners.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
Accurately quantifying short chain chlorinated paraffins (SCCPs) in soil samples with gas chromatograph coupled with electron capture negative ionization mass spectrometry (GC–ECNI-MS) is difficult because many other polychlorinated pollutants are present in the sample matrices. These pollutants (e.g., polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and toxaphene) can cause serious interferences during SCCPs analysis with GC–MS. Four main columns packed with different adsorbents, including silica gel, Florisil and alumina, were investigated in this study to determine their performance for separating interfering pollutants from SCCPs. These experimental results suggest that the optimum cleanup procedure uses a silica gel column and a multilayer silica gel–Florisil composite column. This procedure completely separated 22 PCB congeners, 23 OCPs and three toxaphene congeners from SCCPs. However, p,p′-DDD, cis-nonachlor and o,p′-DDD were not completely removed and only 53% of the total toxaphene was removed. This optimized method was successfully and effectively applied for removing interfering pollutants from real soil samples. SCCPs in 17 soil samples from different land use areas within a suburban region were analyzed with the established method. The concentrations of SCCPs in these samples were between 7 and 541ngg−1 (mean: 84ngg−1). Similar homologue SCCPs patterns were observed between the soil samples collected from different land use areas. In addition, lower chlorinated (Cl6/7) C10- and C11- SCCPs were the dominant congeners.
Highlights
► Establish a two-step cleanup method for accurate analysis of SCCPs in soil. ► The method has good ability to remove known and unknown interferents from SCCPs. ► Obtain preliminary data on SCCPs in soil from Guangzhou area, South China.Development of novel molecularly imprinted magnetic solid-phase extraction materials based on magnetic carbon nanotubes and their application for the determination of gatifloxacin in serum samples coupled with high performance liquid chromatography
14 January 2013,
01:18:17
25 January 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
A novel composite imprinted material, on the basis of magnetic carbon nanotubes (MCNTs)-incorporated layer using gatifloxacin as a template, methacrylic acid as a functional monomer, and ethylene glycol dimethacrylate as a cross-linker, was successfully synthesized by a surface imprinting technique. Adsorption dynamics and a Scatchard adsorption model were employed to evaluate the adsorption process. The results showed that magnetic carbon nanotubes molecularly imprinted polymers (MCNTs@MIP) displayed a rapid dynamic adsorption and a high adsorption capacity of 192.7μg/mg toward GTFX. Applied MCNTs@MIP as a sorbent, a magnetic solid phase extraction method coupled with high performance liquid chromatography (MSPE-HPLC) was developed for the determination of GTFX in serum samples. The recoveries from 79.1±4.8% to 85.3±4.2% were obtained. MCNTs@MIP can not only be collected and separated fast by external magnetic field but also have high surface-to-volume ratio, outstanding mechanical properties and specific recognition toward template molecule. In addition, the MCNTs@MIP could be regenerated, which could be used for five cycles with lost of less than 7.8% of its recovery on average. These analytical results of serum samples display that the proposed method based on MCNTs@MIP is applicable for fast and selective extraction of therapeutic agents from biological fluids.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
A novel composite imprinted material, on the basis of magnetic carbon nanotubes (MCNTs)-incorporated layer using gatifloxacin as a template, methacrylic acid as a functional monomer, and ethylene glycol dimethacrylate as a cross-linker, was successfully synthesized by a surface imprinting technique. Adsorption dynamics and a Scatchard adsorption model were employed to evaluate the adsorption process. The results showed that magnetic carbon nanotubes molecularly imprinted polymers (MCNTs@MIP) displayed a rapid dynamic adsorption and a high adsorption capacity of 192.7μg/mg toward GTFX. Applied MCNTs@MIP as a sorbent, a magnetic solid phase extraction method coupled with high performance liquid chromatography (MSPE-HPLC) was developed for the determination of GTFX in serum samples. The recoveries from 79.1±4.8% to 85.3±4.2% were obtained. MCNTs@MIP can not only be collected and separated fast by external magnetic field but also have high surface-to-volume ratio, outstanding mechanical properties and specific recognition toward template molecule. In addition, the MCNTs@MIP could be regenerated, which could be used for five cycles with lost of less than 7.8% of its recovery on average. These analytical results of serum samples display that the proposed method based on MCNTs@MIP is applicable for fast and selective extraction of therapeutic agents from biological fluids.
Highlights
► A novel method for the highly selective recognition of GTFX was developed. ► Attaching Fe3O4 nanoparticles to carbon nanotubes by a simple solvothermal process. ► Synthesizing MIP on the surface of magnetic carbon nanotubes. ► The composites combined the advantages of Fe3O4 nanoparticles and carbon nanotubes. ► The method is applicable for extraction of therapeutic agents from biological fluids.Selection of operating parameters on the basis of hydrodynamics in centrifugal partition chromatography for the purification of nybomycin derivatives
14 January 2013,
01:18:17
25 January 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
The selection of solvent systems in centrifugal partition chromatography (CPC) is the most critical point in setting up a separation. Therefore, lots of research was done on the topic in the last decades. But the selection of suitable operating parameters (mobile phase flow rate, rotational speed and mode of operation) with respect to hydrodynamics and pressure drop limit in CPC is still mainly driven by experience of the chromatographer. In this work we used hydrodynamic analysis for the prediction of most suitable operating parameters. After selection of different solvent systems with respect to partition coefficients for the target compound the hydrodynamics were visualized. Based on flow pattern and retention the operating parameters were selected for the purification runs of nybomycin derivatives that were carried out with a 200ml FCPC® rotor. The results have proven that the selection of optimized operating parameters by analysis of hydrodynamics only is possible. As the hydrodynamics are predictable by the physical properties of the solvent system the optimized operating parameters can be estimated, too. Additionally, we found that dispersion and especially retention are improved if the less viscous phase is mobile.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
The selection of solvent systems in centrifugal partition chromatography (CPC) is the most critical point in setting up a separation. Therefore, lots of research was done on the topic in the last decades. But the selection of suitable operating parameters (mobile phase flow rate, rotational speed and mode of operation) with respect to hydrodynamics and pressure drop limit in CPC is still mainly driven by experience of the chromatographer. In this work we used hydrodynamic analysis for the prediction of most suitable operating parameters. After selection of different solvent systems with respect to partition coefficients for the target compound the hydrodynamics were visualized. Based on flow pattern and retention the operating parameters were selected for the purification runs of nybomycin derivatives that were carried out with a 200ml FCPC® rotor. The results have proven that the selection of optimized operating parameters by analysis of hydrodynamics only is possible. As the hydrodynamics are predictable by the physical properties of the solvent system the optimized operating parameters can be estimated, too. Additionally, we found that dispersion and especially retention are improved if the less viscous phase is mobile.
Highlights
► First detailed flow visualization of ascending mode in CPC. ► Increased retention if less viscous phase is mobile phase. ► Most suitable volume flow was predictable by hydrodynamics. ► Hydrodynamic efficiency strongly dependent on interfacial tension. ► Optimized operating conditions can be estimated by physical properties only.Hydrodynamic and dispersion behavior in a non-porous silica monolith through fluid dynamic study of a computational mimic reconstructed from sub-micro-tomographic scans
14 January 2013,
01:18:17
25 January 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
An analysis of the transport properties of the bulk homogeneous core of a commercially available silica monolith (Chromolith®) is presented via direct numerical simulations in a topological model reconstructed from 3D nanotomographic scans at isotropic resolutions of 390nm, 290nm and 190nm. The pore and skeleton size distributions were calculated from image analysis and a representative unit cell from each resolution was reconstructed to simulate the hydrodynamic transport properties using Computational Fluid Dynamics (CFD). A 30μm×30μm×30μm unit cell extracted at 190nm resolution was found to be representative of hydrodynamic permeability. Numerical peak parking simulations yielded an axial external obstruction factor (γ e) of 0.8. Mass transfer characteristics of a large non-penetrating molecule (BSA) were evaluated under non-retained conditions so as to elucidate the eddy dispersion contribution to total HETP. Transverse and axial dispersion length scales in the reconstructed model were resolved and related to the structural heterogeneities in the silica monolith. Deviations of simulated HETP from experimental measurements were attributed to a transcolumn dispersion contribution, which amounted to about 90% of the total HETP. The presented approach provides great scope to analyze the contributions of pore network topology to separation performance of silica monoliths (and other porous media) in HPLC applications. A significant reduction in simulation time and memory resources has been observed due to the lower scanning resolution, without significant loss in prediction accuracy.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
An analysis of the transport properties of the bulk homogeneous core of a commercially available silica monolith (Chromolith®) is presented via direct numerical simulations in a topological model reconstructed from 3D nanotomographic scans at isotropic resolutions of 390nm, 290nm and 190nm. The pore and skeleton size distributions were calculated from image analysis and a representative unit cell from each resolution was reconstructed to simulate the hydrodynamic transport properties using Computational Fluid Dynamics (CFD). A 30μm×30μm×30μm unit cell extracted at 190nm resolution was found to be representative of hydrodynamic permeability. Numerical peak parking simulations yielded an axial external obstruction factor (γ e) of 0.8. Mass transfer characteristics of a large non-penetrating molecule (BSA) were evaluated under non-retained conditions so as to elucidate the eddy dispersion contribution to total HETP. Transverse and axial dispersion length scales in the reconstructed model were resolved and related to the structural heterogeneities in the silica monolith. Deviations of simulated HETP from experimental measurements were attributed to a transcolumn dispersion contribution, which amounted to about 90% of the total HETP. The presented approach provides great scope to analyze the contributions of pore network topology to separation performance of silica monoliths (and other porous media) in HPLC applications. A significant reduction in simulation time and memory resources has been observed due to the lower scanning resolution, without significant loss in prediction accuracy.
Highlights
► Macropore network of a silica monolith is scanned at three isotropic resolutions. ► 30μm cube at 190nm resolution is representative of porosity and hydrodynamics. ► Dispersion simulations allude to a detrimental transcolumn dispersion contribution. ► Lower scanning resolution does not adversely affect accuracy of model.Comparing two models of gradient elution in counter-current chromatography
14 January 2013,
01:18:17
25 January 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
Gradient change of mobile phase composition is commonly used in liquid chromatography to shorten analysis duration. Gradient elution is possible in counter-current chromatography if it is demonstrated that the mobile phase composition changes are not associated with liquid stationary phase composition changes. Also, the solute distribution ratios in initial (1) and final (2) eluting systems must be known. If the solute distribution ratios during the changing mobile phase composition are modeled, the full gradient separation can be modeled using classical equations of liquid chromatography. Another approach allowed modeling empirically the gradient step. It considered the decreasing volume of mobile phase 1 and the increasing volume of mobile phase 2 used at each gradient time to derive a very simple equation. The two equations were compared computing the retention volumes of five test solutes. A remarkable agreement was observed considering the very different mathematical expressions of the two models. The step-gradient method was also modeled and its results compared to those of the linear gradient method.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
Gradient change of mobile phase composition is commonly used in liquid chromatography to shorten analysis duration. Gradient elution is possible in counter-current chromatography if it is demonstrated that the mobile phase composition changes are not associated with liquid stationary phase composition changes. Also, the solute distribution ratios in initial (1) and final (2) eluting systems must be known. If the solute distribution ratios during the changing mobile phase composition are modeled, the full gradient separation can be modeled using classical equations of liquid chromatography. Another approach allowed modeling empirically the gradient step. It considered the decreasing volume of mobile phase 1 and the increasing volume of mobile phase 2 used at each gradient time to derive a very simple equation. The two equations were compared computing the retention volumes of five test solutes. A remarkable agreement was observed considering the very different mathematical expressions of the two models. The step-gradient method was also modeled and its results compared to those of the linear gradient method.
Highlights
► Full mathematical developments of two models for linear gradient separations in CCC. ► Modeling of the step-gradient procedure. ► Comparison of the results produced by the two different linear gradient models. ► Comparison between linear and step-gradient results.Analysis of amino acid–water interactions by partitioning in aqueous two-phase systems. I—Amino acids with non-polar side-chains
14 January 2013,
01:18:17
25 January 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
Partition ratios of 10 l-amino acids with non-polar side chains (Gly, Ala, Val, nor-Val, Ile, Leu, nor-Leu, Phe, Trp and Pro) were measured in ten different polymer/polymer aqueous two-phase systems (ATPS) containing 0.15M NaCl in 0.01M phosphate buffer, pH 7.4. The solute-specific coefficients representing the solute dipole–dipole, hydrogen bonding and electrostatic interactions with aqueous environment for the compounds examined were determined by the multiple linear regression analysis using the modified linear solvation energy relationship equation. It is shown that linear combinations of these coefficients are correlated with the amino acid lipophilicity/hydrophobicity scales reported in the literature. The results obtained imply that the solute-specific coefficients may be used as solute descriptors for quantitative structure–property relationship (QSPR) analysis.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
Partition ratios of 10 l-amino acids with non-polar side chains (Gly, Ala, Val, nor-Val, Ile, Leu, nor-Leu, Phe, Trp and Pro) were measured in ten different polymer/polymer aqueous two-phase systems (ATPS) containing 0.15M NaCl in 0.01M phosphate buffer, pH 7.4. The solute-specific coefficients representing the solute dipole–dipole, hydrogen bonding and electrostatic interactions with aqueous environment for the compounds examined were determined by the multiple linear regression analysis using the modified linear solvation energy relationship equation. It is shown that linear combinations of these coefficients are correlated with the amino acid lipophilicity/hydrophobicity scales reported in the literature. The results obtained imply that the solute-specific coefficients may be used as solute descriptors for quantitative structure–property relationship (QSPR) analysis.
Highlights
► Partition ratios of 10 l-amino acids were measured in 10 ATPS. ► Using the solvatochromic approach solute-specific coefficients are obtained. ► The coefficients obtained are correlated with different lipophilicity/hydrophobicity scales. ► They may be used for quantitative structure–property relationship (QSPR) analysis.A novel solid-phase extraction for the concentration of sweeteners in water and analysis by ion-pair liquid chromatography–triple quadrupole mass spectrometry
14 January 2013,
01:18:17
25 January 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
A highly sensitive method for the simultaneous trace (ng/L) quantification of seven commonly used artificial sweeteners in a variety of water samples using solid-phase extraction and ion-pair high-performance liquid chromatography (HPLC) triple quadrupole mass spectrometer with an electrospray ionization source (ESI-MS) in negative ion multiple reaction monitoring mode was developed. Ten solid phase extraction (SPE) cartridges were tested to evaluate their applicability for the pre-concentration of the analytes, and their loading and eluting parameters were optimized. Satisfactory recoveries (77–99%) of all of the studied sweeteners were obtained using a Poly-Sery PWAX cartridge with 25mM sodium acetate solution (pH 4) as wash buffer and methanol containing 1mM tris (hydroxymethyl) amino methane (TRIS) as eluent. The method is sound and does not require pH adjustment or buffering of water samples. The HPLC separation was performed on an Athena C18-WP column with water and acetonitrile, both containing 5mM ammonium acetate and 1mM TRIS as mobile phases, in gradient elution mode. The linearity, precision, and accuracy of the method were evaluated, and good reproducibility was obtained. Method quantification limits varied between 0.4 and 7.5ng/L for different water samples. The post-extraction spike method was applied to assess matrix effects, and quantification was achieved using internal standard calibration to overcome the unavoidable matrix effects during ESI-MS analysis. The method was applied to the analysis of thirteen water samples from Tianjin, China, including wastewater, tap water, surface water, and groundwater. The method described here is time-saving, accurate and precise, and is suitable for monitoring artificial sweeteners in different water matrices.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
A highly sensitive method for the simultaneous trace (ng/L) quantification of seven commonly used artificial sweeteners in a variety of water samples using solid-phase extraction and ion-pair high-performance liquid chromatography (HPLC) triple quadrupole mass spectrometer with an electrospray ionization source (ESI-MS) in negative ion multiple reaction monitoring mode was developed. Ten solid phase extraction (SPE) cartridges were tested to evaluate their applicability for the pre-concentration of the analytes, and their loading and eluting parameters were optimized. Satisfactory recoveries (77–99%) of all of the studied sweeteners were obtained using a Poly-Sery PWAX cartridge with 25mM sodium acetate solution (pH 4) as wash buffer and methanol containing 1mM tris (hydroxymethyl) amino methane (TRIS) as eluent. The method is sound and does not require pH adjustment or buffering of water samples. The HPLC separation was performed on an Athena C18-WP column with water and acetonitrile, both containing 5mM ammonium acetate and 1mM TRIS as mobile phases, in gradient elution mode. The linearity, precision, and accuracy of the method were evaluated, and good reproducibility was obtained. Method quantification limits varied between 0.4 and 7.5ng/L for different water samples. The post-extraction spike method was applied to assess matrix effects, and quantification was achieved using internal standard calibration to overcome the unavoidable matrix effects during ESI-MS analysis. The method was applied to the analysis of thirteen water samples from Tianjin, China, including wastewater, tap water, surface water, and groundwater. The method described here is time-saving, accurate and precise, and is suitable for monitoring artificial sweeteners in different water matrices.
Highlights
► A novel SPE procedure for the extraction of artificial sweeteners was developed. ► Satisfactory recoveries were obtained without pH adjustment of the samples. ► A sensitive method for the quantification of artificial sweeteners was developed. ► The method was applied for the analysis of thirteen water samples from China. ► Artificial sweeteners occurred ubiquitously in the investigated samples.Cross-linker effects on the separation efficiency on (poly)methacrylate capillary monolithic columns. Part I. Reversed-phase liquid chromatography
14 January 2013,
01:18:17
25 January 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
We synthesized 8 polymethacrylate monolithic capillary columns using laurylmethacrylate functional monomer and various cross-linking monomers differing in the polarity and size. The efficiency of monolithic columns for low-molecular compounds significantly improved with increasing number of repeat non-polar methylene groups in the cross-linker molecules, correlating with greater proportion of small pores with size less than 50nm. The best efficiency with HETP=25μm for alkylbenzenes was achieved for columns prepared using hexamethylene dimethacrylate (HEDMA). Columns prepared with polar (poly)oxyethylene dimethacrylate cross-linkers show also improved efficiency with increasing chain length and generally better performance in comparison to the (poly)methylene dimethacrylate cross-linkers of comparable size, however with less apparent effects of the chain lengths on the pore distribution. The monolithic columns prepared with tetraoxyethylene dimethacrylate (TeEDMA) showed the best efficiency of all the columns tested, corresponding to HETP=15μm (approx. 70,000 theoretical plates/m), show excellent column-to-column reproducibility with standard deviations of 2.5% in retention times, good permeability and low mass transfer resistance, so that is suitable for fast separation of low-molecular compounds in 2min or less. By modification of the fused-silica capillary inner walls pre-treatment procedure, very good long-term stability was achieved even in 0.5mm i.d. capillary format. The TeEDMA column can be also used for size-exclusion chromatography of lower non-polar synthetic polymers, whereas it is less suitable for separations of proteins than the HEDMA column.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
We synthesized 8 polymethacrylate monolithic capillary columns using laurylmethacrylate functional monomer and various cross-linking monomers differing in the polarity and size. The efficiency of monolithic columns for low-molecular compounds significantly improved with increasing number of repeat non-polar methylene groups in the cross-linker molecules, correlating with greater proportion of small pores with size less than 50nm. The best efficiency with HETP=25μm for alkylbenzenes was achieved for columns prepared using hexamethylene dimethacrylate (HEDMA). Columns prepared with polar (poly)oxyethylene dimethacrylate cross-linkers show also improved efficiency with increasing chain length and generally better performance in comparison to the (poly)methylene dimethacrylate cross-linkers of comparable size, however with less apparent effects of the chain lengths on the pore distribution. The monolithic columns prepared with tetraoxyethylene dimethacrylate (TeEDMA) showed the best efficiency of all the columns tested, corresponding to HETP=15μm (approx. 70,000 theoretical plates/m), show excellent column-to-column reproducibility with standard deviations of 2.5% in retention times, good permeability and low mass transfer resistance, so that is suitable for fast separation of low-molecular compounds in 2min or less. By modification of the fused-silica capillary inner walls pre-treatment procedure, very good long-term stability was achieved even in 0.5mm i.d. capillary format. The TeEDMA column can be also used for size-exclusion chromatography of lower non-polar synthetic polymers, whereas it is less suitable for separations of proteins than the HEDMA column.
Highlights
► We prepared monolithic polymethacrylate capillary columns using various cross-linkers. ► The column efficiency improves with increasing length and polarity of cross-linkers. ► 70,000 theoretical plates/m were achieved for isocratic separation of small molecules. ► The preparation of columns shows excellent column-to-column reproducibility. ► Polymerization conditions can be tuned for separations of small molecules or polymers.Separation of one-pot procedure released O-glycans as 1-phenyl-3-methyl-5-pyrazolone derivatives by hydrophilic interaction and reversed-phase liquid chromatography followed by identification using electrospray mass spectrometry and tandem mass spectrometry
14 January 2013,
01:18:17
25 January 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
Qualitative and quantitative analysis of naturally-occurring complex glycans is essential for glycomics, which focuses on the studies of structure–function correlations of saccharides. We previously reported a one-pot procedure for the non-reductive release from glycoproteins and in situ labeling with 1-phenyl-3-methyl-5-pyrazolone (PMP) of O-glycans (C. Wang et al., Proteomics 11 (2011) 4229). Here we describe an HPLC-based O-glycan analytical strategy that combines a range of techniques including the one-pot procedure, independent separation by hydrophilic interaction liquid chromatography (HILIC) and reversed-phase high-performance liquid chromatography (RP-HPLC) and identification by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). The complex mixtures of both neutral and sialylated O-glycans as bis-PMP derivatives released from glycoproteins using the one-pot procedure could be well separated by HILIC based on their size or by RP-HPLC depending on the type of linkage and their resulting three-dimensional (3D) structure, and their structure could be characterized by the ESI-MS and MS/MS analysis of the eluted glycan fractions. The validity of the current strategy was confirmed by the analysis of O-glycans released by the one-pot procedure from some standard glycoproteins, including porcine stomach mucin (PSM), bovine submaxillary mucin (BSM) and bovine fetuin. The applicability of the current method to complex biological samples was also demonstrated by the analysis of mucin-type glycans from fetal bovine serum (FBS) and frog egg–jelly coat (FEC). This strategy, a powerful analytical tool that features the combination of different techniques, is useful for the qualitative and quantitative O-glycan analysis of more complex biological samples and has a potential for constructing an O-glycan analysis and structure database.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
Qualitative and quantitative analysis of naturally-occurring complex glycans is essential for glycomics, which focuses on the studies of structure–function correlations of saccharides. We previously reported a one-pot procedure for the non-reductive release from glycoproteins and in situ labeling with 1-phenyl-3-methyl-5-pyrazolone (PMP) of O-glycans (C. Wang et al., Proteomics 11 (2011) 4229). Here we describe an HPLC-based O-glycan analytical strategy that combines a range of techniques including the one-pot procedure, independent separation by hydrophilic interaction liquid chromatography (HILIC) and reversed-phase high-performance liquid chromatography (RP-HPLC) and identification by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). The complex mixtures of both neutral and sialylated O-glycans as bis-PMP derivatives released from glycoproteins using the one-pot procedure could be well separated by HILIC based on their size or by RP-HPLC depending on the type of linkage and their resulting three-dimensional (3D) structure, and their structure could be characterized by the ESI-MS and MS/MS analysis of the eluted glycan fractions. The validity of the current strategy was confirmed by the analysis of O-glycans released by the one-pot procedure from some standard glycoproteins, including porcine stomach mucin (PSM), bovine submaxillary mucin (BSM) and bovine fetuin. The applicability of the current method to complex biological samples was also demonstrated by the analysis of mucin-type glycans from fetal bovine serum (FBS) and frog egg–jelly coat (FEC). This strategy, a powerful analytical tool that features the combination of different techniques, is useful for the qualitative and quantitative O-glycan analysis of more complex biological samples and has a potential for constructing an O-glycan analysis and structure database.
Highlights
► The current strategy is powerful due to the combination of different techniques. ► PMP derivatives of O-glycans are separated by HILIC depending on their size. ► PMP derivatives of O-glycans are separated by RP-HPLC based on their 3D-structure. ► This strategy has advantages over conventional O-glycan analysis methods. ► This strategy could be utilized for constructing an O-glycan analysis database.Quantification aspects of constant pressure (ultra) high pressure liquid chromatography using mass-sensitive detectors with a nebulizing interface
14 January 2013,
01:18:17
25 January 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
The present contribution investigates the quantitation aspects of mass-sensitive detectors with nebulizing interface (ESI-MSD, ELSD, CAD) in the constant pressure gradient elution mode. In this operation mode, the pressure is controlled and maintained at a set value and the liquid flow rate will vary according to the inverse mobile phase viscosity. As the pressure is continuously kept at the allowable maximum during the entire gradient run, the average liquid flow rate is higher compared to that in the conventional constant flow rate operation mode, thus shortening the analysis time. The following three mass-sensitive detectors were investigated: mass spectrometry detector (MS), evaporative light scattering detector (ELSD) and charged aerosol detector (CAD) and a wide variety of samples (phenones, polyaromatic hydrocarbons, wine, cocoa butter) has been considered. It was found that the nebulizing efficiency of the LC-interfaces of the three detectors under consideration changes with the increasing liquid flow rate. For the MS, the increasing flow rate leads to a lower peak area whereas for the ELSD the peak area increases compared to the constant flow rate mode. The peak area obtained with a CAD is rather insensitive to the liquid flow rate. The reproducibility of the peak area remains similar in both modes, although variation in system permeability compromises the ‘long-term’ reproducibility. This problem can however be overcome by running a flow rate program with an optimized flow rate and composition profile obtained from the constant pressure mode. In this case, the quantification remains reproducibile, despite any occuring variations of the system permeability. Furthermore, the same fragmentation pattern (MS) has been found in the constant pressure mode compared to the customary constant flow rate mode.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1274
The present contribution investigates the quantitation aspects of mass-sensitive detectors with nebulizing interface (ESI-MSD, ELSD, CAD) in the constant pressure gradient elution mode. In this operation mode, the pressure is controlled and maintained at a set value and the liquid flow rate will vary according to the inverse mobile phase viscosity. As the pressure is continuously kept at the allowable maximum during the entire gradient run, the average liquid flow rate is higher compared to that in the conventional constant flow rate operation mode, thus shortening the analysis time. The following three mass-sensitive detectors were investigated: mass spectrometry detector (MS), evaporative light scattering detector (ELSD) and charged aerosol detector (CAD) and a wide variety of samples (phenones, polyaromatic hydrocarbons, wine, cocoa butter) has been considered. It was found that the nebulizing efficiency of the LC-interfaces of the three detectors under consideration changes with the increasing liquid flow rate. For the MS, the increasing flow rate leads to a lower peak area whereas for the ELSD the peak area increases compared to the constant flow rate mode. The peak area obtained with a CAD is rather insensitive to the liquid flow rate. The reproducibility of the peak area remains similar in both modes, although variation in system permeability compromises the ‘long-term’ reproducibility. This problem can however be overcome by running a flow rate program with an optimized flow rate and composition profile obtained from the constant pressure mode. In this case, the quantification remains reproducibile, despite any occuring variations of the system permeability. Furthermore, the same fragmentation pattern (MS) has been found in the constant pressure mode compared to the customary constant flow rate mode.
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