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Selected papers from the latest issue:
Gas chromatography/mass spectrometry comprehensive analysis of organophosphorus, brominated flame retardants, by-products and formulation intermediates in water
14 May 2012,
23:16:24
Publication year:
2012
Source:Journal of Chromatography A, Volume 1241
Joyce Cristale, Jordi Quintana, Roser Chaler, Francesc Ventura, Silvia Lacorte
A multiresidue method based on gas chromatography coupled to quadrupole mass spectrometry was developed to determine organophosphorus flame retardants, polybromodiphenyl ethers (BDEs 28, 47, 99, 100, 153, 154, 183 and 209), new brominated flame retardants, bromophenols, bromoanilines, bromotoluenes and bromoanisoles in water. Two ionization techniques (electron ionization – EI, and electron capture negative ionization – ECNI) and two acquisition modes (selected ion monitoring – SIM, and selected reaction monitoring – SRM) were compared as regards to mass spectral characterization, sensitivity and quantification capabilities. The highest sensitivity, at expenses of identification capacity, was obtained by GC–ECNI-MS/SIM for most of the compounds analyzed, mainly for PBDEs and decabromodiphenyl ethane while GC–EI-MS/MS in SRM was the most selective technique and permitted the identification of target compounds at the pg level, and identification capabilities increased when real samples were analyzed. This method was further used to evaluate the presence and behavior of flame retardants within a drinking water treatment facility. Organophosphorus flame retardants were the only compounds detected in influent waters at levels of 0.32–0.03μgL−1, and their elimination throughout the different treatment stages was evaluated.
Source:Journal of Chromatography A, Volume 1241
Joyce Cristale, Jordi Quintana, Roser Chaler, Francesc Ventura, Silvia Lacorte
A multiresidue method based on gas chromatography coupled to quadrupole mass spectrometry was developed to determine organophosphorus flame retardants, polybromodiphenyl ethers (BDEs 28, 47, 99, 100, 153, 154, 183 and 209), new brominated flame retardants, bromophenols, bromoanilines, bromotoluenes and bromoanisoles in water. Two ionization techniques (electron ionization – EI, and electron capture negative ionization – ECNI) and two acquisition modes (selected ion monitoring – SIM, and selected reaction monitoring – SRM) were compared as regards to mass spectral characterization, sensitivity and quantification capabilities. The highest sensitivity, at expenses of identification capacity, was obtained by GC–ECNI-MS/SIM for most of the compounds analyzed, mainly for PBDEs and decabromodiphenyl ethane while GC–EI-MS/MS in SRM was the most selective technique and permitted the identification of target compounds at the pg level, and identification capabilities increased when real samples were analyzed. This method was further used to evaluate the presence and behavior of flame retardants within a drinking water treatment facility. Organophosphorus flame retardants were the only compounds detected in influent waters at levels of 0.32–0.03μgL−1, and their elimination throughout the different treatment stages was evaluated.
Dynamic liquid–liquid–solid microextraction based on molecularly imprinted polymer filaments on-line coupling to high performance liquid chromatography for direct analysis of estrogens in complex samples
14 May 2012,
23:16:24
Publication year:
2012
Source:Journal of Chromatography A, Volume 1241
Qisheng Zhong, Yufei Hu, Yuling Hu, Gongke Li
A novel sample preparation technique termed dynamic liquid–liquid–solid microextraction (DLLSME) was developed and on-line coupled to high performance liquid chromatography (HPLC) for direct extraction, desorption, and analysis of trace estrogens in complex samples. The DLLSME consists of the aqueous donor phase, the organic medium phase and the molecularly imprinted polymer filaments (MIPFs) as solid acceptor phase. The organic solvent with lesser density was directly added on top of the aqueous sample, and the dynamic extraction was performed by circulating the organic solvent through the MIPFs inserted into a PEEK tube which served as an extraction and desorption chamber. Afterwards, the extracted analytes on the MIPFs were on-line desorbed and then introduced into the HPLC for analysis. To evaluate the feasibility of the on-line system, a new DLLSME-HPLC method was developed for the analysis of five estrogens in aqueous samples by using 17β-estradiol MIPFs as the solid phase. Under the optimized conditions, the enrichment factors of 51–70, limits of detection of 0.08–0.25μg/L and precision within 4.5–6.9% were achieved. Furthermore, the proposed method was applied to the analysis of real samples including urine, milk and skin toner, satisfactory recovery (81.9–99.8%) and reproducibility (4.1–7.9%) were obtained. Especially, 0.59μg/L of 17β-estradiol was determined in female urine sample. The DLLSME offers an attractive alternative for direct analysis of trace analytes in aqueous samples and could potentially be extended to other adsorptive materials.
Source:Journal of Chromatography A, Volume 1241
Qisheng Zhong, Yufei Hu, Yuling Hu, Gongke Li
A novel sample preparation technique termed dynamic liquid–liquid–solid microextraction (DLLSME) was developed and on-line coupled to high performance liquid chromatography (HPLC) for direct extraction, desorption, and analysis of trace estrogens in complex samples. The DLLSME consists of the aqueous donor phase, the organic medium phase and the molecularly imprinted polymer filaments (MIPFs) as solid acceptor phase. The organic solvent with lesser density was directly added on top of the aqueous sample, and the dynamic extraction was performed by circulating the organic solvent through the MIPFs inserted into a PEEK tube which served as an extraction and desorption chamber. Afterwards, the extracted analytes on the MIPFs were on-line desorbed and then introduced into the HPLC for analysis. To evaluate the feasibility of the on-line system, a new DLLSME-HPLC method was developed for the analysis of five estrogens in aqueous samples by using 17β-estradiol MIPFs as the solid phase. Under the optimized conditions, the enrichment factors of 51–70, limits of detection of 0.08–0.25μg/L and precision within 4.5–6.9% were achieved. Furthermore, the proposed method was applied to the analysis of real samples including urine, milk and skin toner, satisfactory recovery (81.9–99.8%) and reproducibility (4.1–7.9%) were obtained. Especially, 0.59μg/L of 17β-estradiol was determined in female urine sample. The DLLSME offers an attractive alternative for direct analysis of trace analytes in aqueous samples and could potentially be extended to other adsorptive materials.
Determination of alkylphenols and phthalate esters in vegetables and migration studies from their packages by means of stir bar sorptive extraction coupled to gas chromatography–mass spectrometry
14 May 2012,
23:16:24
Publication year:
2012
Source:Journal of Chromatography A, Volume 1241
J.I. Cacho, N. Campillo, P. Viñas, M. Hernández-Córdoba
This paper describes a method for the determination of three alkylphenols (APs), 4-tert-octylphenol (tOP), 4-n-octylphenol (OP) and 4-nonylphenol (NP), and six phthalate esters (PEs), dimethylphthalate (DMP), diethylphthalate (DEP), di-n-butylphthalate (DBP), n-butylbenzylphthalate (BBP), di-2-ethylhexylphthalate (DEHP) and di-n-octylphthalate (DOP), in vegetables using stir bar sorptive extraction (SBSE) in combination with thermal desorption–gas chromatography–mass spectrometry (TD–GC–MS). Ultrasonic radiation was used to extract the analytes from the solid food matrix, and the extract obtained was preconcentrated by SBSE. The different parameters affecting both stages were carefully optimized. The method was applied to analyze commercial vegetables, in the form of plastic packed salads and canned greens, as well as the corresponding filling liquids of the canned food. Quantification of the samples was carried out against aqueous standards using an internal standard (anthracene). The analysis of a 2g vegetable sample provided detection limits between 12.7 and 105.8pgg−1 for OP and DEHP, respectively. Migration studies from the plastic packages of the vegetables samples analyzed were carried out. DEP, DBP and DEHP were found to have migrated from the bags to the simulant and the same compounds were quantified in lettuce, corn salad, arugula, parsley and chard, at concentration levels in the 8–51ngg−1 range. However, OP and NP were found in only two vegetable samples and one filling liquid, but neither was detected in any package. The proposed method provided recoveries of 83–118%.
Source:Journal of Chromatography A, Volume 1241
J.I. Cacho, N. Campillo, P. Viñas, M. Hernández-Córdoba
This paper describes a method for the determination of three alkylphenols (APs), 4-tert-octylphenol (tOP), 4-n-octylphenol (OP) and 4-nonylphenol (NP), and six phthalate esters (PEs), dimethylphthalate (DMP), diethylphthalate (DEP), di-n-butylphthalate (DBP), n-butylbenzylphthalate (BBP), di-2-ethylhexylphthalate (DEHP) and di-n-octylphthalate (DOP), in vegetables using stir bar sorptive extraction (SBSE) in combination with thermal desorption–gas chromatography–mass spectrometry (TD–GC–MS). Ultrasonic radiation was used to extract the analytes from the solid food matrix, and the extract obtained was preconcentrated by SBSE. The different parameters affecting both stages were carefully optimized. The method was applied to analyze commercial vegetables, in the form of plastic packed salads and canned greens, as well as the corresponding filling liquids of the canned food. Quantification of the samples was carried out against aqueous standards using an internal standard (anthracene). The analysis of a 2g vegetable sample provided detection limits between 12.7 and 105.8pgg−1 for OP and DEHP, respectively. Migration studies from the plastic packages of the vegetables samples analyzed were carried out. DEP, DBP and DEHP were found to have migrated from the bags to the simulant and the same compounds were quantified in lettuce, corn salad, arugula, parsley and chard, at concentration levels in the 8–51ngg−1 range. However, OP and NP were found in only two vegetable samples and one filling liquid, but neither was detected in any package. The proposed method provided recoveries of 83–118%.
Analysis of common and emerging brominated flame retardants in house dust using ultrasonic assisted solvent extraction and on-line sample preparation via column switching with liquid chromatography–mass spectrometry
14 May 2012,
23:16:24
Publication year:
2012
Source:Journal of Chromatography A, Volume 1241
E.K. Kopp, H. Fromme, W. Völkel
Brominated flame retardants (BFRs) are persistent and widespread chemicals. Therefore human beings are exposed to BFRs. House dust may be one source of exposure and contains a lot of xenobiotics in relatively high concentrations. In contrast to common GC–MS based methods here an online LC–MS/MS method is presented to quantify 16 BFRs in dust using ultrasonic solvent extraction as a single sample work up step. LOQ from 0.6 (tetrabromobisphenol A) to 80 (polybrominated diphenylethers (BDE 28) ng/g dust were achieved. Data for accuracy, precision and recovery are presented and are comparable to common LC–MS/MS methods in different matrices. In addition 5 real house dust samples were analyzed with high concentration (535ng/g) for bis(2-ethyl-1-hexyl)tetrabromophthalate which is a novel alternative BFRs to replace common BDE's.
Source:Journal of Chromatography A, Volume 1241
E.K. Kopp, H. Fromme, W. Völkel
Brominated flame retardants (BFRs) are persistent and widespread chemicals. Therefore human beings are exposed to BFRs. House dust may be one source of exposure and contains a lot of xenobiotics in relatively high concentrations. In contrast to common GC–MS based methods here an online LC–MS/MS method is presented to quantify 16 BFRs in dust using ultrasonic solvent extraction as a single sample work up step. LOQ from 0.6 (tetrabromobisphenol A) to 80 (polybrominated diphenylethers (BDE 28) ng/g dust were achieved. Data for accuracy, precision and recovery are presented and are comparable to common LC–MS/MS methods in different matrices. In addition 5 real house dust samples were analyzed with high concentration (535ng/g) for bis(2-ethyl-1-hexyl)tetrabromophthalate which is a novel alternative BFRs to replace common BDE's.
Risk–benefit evaluation of on-line high-performance liquid chromatography analysis for pooling decisions in large-scale chromatography
14 May 2012,
23:16:24
Publication year:
2012
Source:Journal of Chromatography A, Volume 1241
Oliver Kaltenbrunner, Yuefeng Lu, Ashutosh Sharma, Ken Lawson, Tim Tressel
In the production of a human therapeutic protein from inclusion bodies, product related impurities of very similar size and charge to the product are created as byproducts of the refold process. Their removal is usually challenging even when using chromatography with high performance resins and elution by shallow linear gradients. Additionally, performing this type of separation for commercial production adds increased complexity. To maximize productivity, columns are loaded so high that product elution profiles are not well separated from the impurities and pooling decisions are challenging. In this paper, conventional UV pooling based on fractionation or predefined absorbance based criteria will be compared to pooling based on fast on-line HPLC analytic. The development and implementation in a GMP process will be shown for a specific challenging separation by hydrophobic interaction chromatography. The different approaches have their unique complexities, timelines, uncertainties, and risks during development and implementation as well as during manufacturing. This study presents a probabilistic framework for quantitative comparison of two processes with unequal variability and uncertainty to evaluate the potential benefits of a PAT technology for its routine use in GMP Bioprocess manufacturing.
Source:Journal of Chromatography A, Volume 1241
Oliver Kaltenbrunner, Yuefeng Lu, Ashutosh Sharma, Ken Lawson, Tim Tressel
In the production of a human therapeutic protein from inclusion bodies, product related impurities of very similar size and charge to the product are created as byproducts of the refold process. Their removal is usually challenging even when using chromatography with high performance resins and elution by shallow linear gradients. Additionally, performing this type of separation for commercial production adds increased complexity. To maximize productivity, columns are loaded so high that product elution profiles are not well separated from the impurities and pooling decisions are challenging. In this paper, conventional UV pooling based on fractionation or predefined absorbance based criteria will be compared to pooling based on fast on-line HPLC analytic. The development and implementation in a GMP process will be shown for a specific challenging separation by hydrophobic interaction chromatography. The different approaches have their unique complexities, timelines, uncertainties, and risks during development and implementation as well as during manufacturing. This study presents a probabilistic framework for quantitative comparison of two processes with unequal variability and uncertainty to evaluate the potential benefits of a PAT technology for its routine use in GMP Bioprocess manufacturing.
Analysis of multiple quaternary ammonium compounds in the brain using tandem capillary column separation and high resolution mass spectrometric detection
14 May 2012,
23:16:24
Publication year:
2012
Source:Journal of Chromatography A, Volume 1241
Sara Falasca, Filomena Petruzziello, Robert Kretz, Gregor Rainer, Xiaozhe Zhang
Endogenous quaternary ammonium compounds are involved in various physiological processes in the central nervous system. In the present study, eleven quaternary ammonium compounds, including acetylcholine, choline, carnitine, acetylcarnitine and seven other acylcarnitines of low polarity, were analyzed from brain extracts using a two dimension capillary liquid chromatography–Fourier transform mass spectrometry method. To deal with their large difference in hydrophobicities, tandem coupling between reversed phase and hydrophilic interaction chromatography columns was used to separate all the targeted quaternary ammonium compounds. Using high accuracy mass spectrometry in selected ion monitoring mode, all the compounds could be detected from each brain sample with high selectivity. The developed method was applied for the relative quantification of these quaternary ammonium compounds in three different brain regions of tree shrews: prefrontal cortex, striatum, and hippocampus. The comparative analysis showed that quaternary ammonium compounds were differentially distributed across the three brain areas. The analytical method proved to be highly sensitive and reliable for simultaneous determination of all the targeted analytes from brain samples.
Source:Journal of Chromatography A, Volume 1241
Sara Falasca, Filomena Petruzziello, Robert Kretz, Gregor Rainer, Xiaozhe Zhang
Endogenous quaternary ammonium compounds are involved in various physiological processes in the central nervous system. In the present study, eleven quaternary ammonium compounds, including acetylcholine, choline, carnitine, acetylcarnitine and seven other acylcarnitines of low polarity, were analyzed from brain extracts using a two dimension capillary liquid chromatography–Fourier transform mass spectrometry method. To deal with their large difference in hydrophobicities, tandem coupling between reversed phase and hydrophilic interaction chromatography columns was used to separate all the targeted quaternary ammonium compounds. Using high accuracy mass spectrometry in selected ion monitoring mode, all the compounds could be detected from each brain sample with high selectivity. The developed method was applied for the relative quantification of these quaternary ammonium compounds in three different brain regions of tree shrews: prefrontal cortex, striatum, and hippocampus. The comparative analysis showed that quaternary ammonium compounds were differentially distributed across the three brain areas. The analytical method proved to be highly sensitive and reliable for simultaneous determination of all the targeted analytes from brain samples.
Liquid chromatography–tandem mass spectrometry method for the quantification of mycophenolic acid and its phenolic glucuronide in saliva and plasma using a standardized saliva collection device
14 May 2012,
23:16:24
Publication year:
2012
Source:Journal of Chromatography A, Volume 1241
Martin H.J. Wiesen, Fedja Farowski, Markus Feldkötter, Bernd Hoppe, Carsten Müller
A liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed for simultaneous quantification of mycophenolic acid (MPA) and its phenolic glucuronide (MPAG) in saliva and plasma. Saliva was collected and processed using a standardized commercially available collection device. Sample preparation comprised of protein precipitation with acetonitrile and subsequent centrifugation, followed by evaporation and reconstitution with mobile phase. A labeled isotope of MPA was used as internal standard, and chromatographic separation was achieved on a C18 column with an isocratic flow. LC–MS/MS detection was performed using a triple-stage quadrupole mass spectrometer working in selected reaction monitoring mode with positive electrospray ionization (ESI). The analytes were quantified in a single run within 2min. For saliva, linearity was demonstrated over the concentration range of 5.0 to 400.0ng/ml for both MPA and MPAG, and from 0.08 to 20.00μg/ml for MPA and 0.4 to 100.0μg/ml for MPAG in plasma. The lower limits of quantification for MPA and MPAG were 0.07 and 0.80ng/ml in saliva, and 0.002 and 0.009μg/ml in plasma, respectively. Inter- and intra-day precisions expressed as relative standard deviation (RSD) and accuracies were less than 15%. The recoveries for MPA and MPAG from the collection device's swab were higher than 90%. Sample stability was confirmed for bench times up to 24h at room temperature. The method was validated according to International Conference on Harmonization (ICH) guidelines Q2 (R1) Validation of Analytical Procedures. The applicability of the method was tested in a renal pediatric patient. Based on a limited sampling strategy, MPA saliva and plasma concentrations were found in good agreement with each other. We suggest that the described method is suitable to analyze saliva and plasma samples of small volumes for therapeutic drug monitoring (TDM) and pharmacokinetic studies in pediatric patients.
Source:Journal of Chromatography A, Volume 1241
Martin H.J. Wiesen, Fedja Farowski, Markus Feldkötter, Bernd Hoppe, Carsten Müller
A liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed for simultaneous quantification of mycophenolic acid (MPA) and its phenolic glucuronide (MPAG) in saliva and plasma. Saliva was collected and processed using a standardized commercially available collection device. Sample preparation comprised of protein precipitation with acetonitrile and subsequent centrifugation, followed by evaporation and reconstitution with mobile phase. A labeled isotope of MPA was used as internal standard, and chromatographic separation was achieved on a C18 column with an isocratic flow. LC–MS/MS detection was performed using a triple-stage quadrupole mass spectrometer working in selected reaction monitoring mode with positive electrospray ionization (ESI). The analytes were quantified in a single run within 2min. For saliva, linearity was demonstrated over the concentration range of 5.0 to 400.0ng/ml for both MPA and MPAG, and from 0.08 to 20.00μg/ml for MPA and 0.4 to 100.0μg/ml for MPAG in plasma. The lower limits of quantification for MPA and MPAG were 0.07 and 0.80ng/ml in saliva, and 0.002 and 0.009μg/ml in plasma, respectively. Inter- and intra-day precisions expressed as relative standard deviation (RSD) and accuracies were less than 15%. The recoveries for MPA and MPAG from the collection device's swab were higher than 90%. Sample stability was confirmed for bench times up to 24h at room temperature. The method was validated according to International Conference on Harmonization (ICH) guidelines Q2 (R1) Validation of Analytical Procedures. The applicability of the method was tested in a renal pediatric patient. Based on a limited sampling strategy, MPA saliva and plasma concentrations were found in good agreement with each other. We suggest that the described method is suitable to analyze saliva and plasma samples of small volumes for therapeutic drug monitoring (TDM) and pharmacokinetic studies in pediatric patients.
Enantioseparation and chiral recognition mechanism of new chiral derivatives of xanthones on macrocyclic antibiotic stationary phases
14 May 2012,
23:16:24
Publication year:
2012
Source:Journal of Chromatography A, Volume 1241
Carla Fernandes, Maria Elizabeth Tiritan, Quezia Cass, Visvaldas Kairys, Miguel Xavier Fernandes, Madalena Pinto
A chiral HPLC method using four macrocyclic antibiotic chiral stationary phases (CSPs) has been investigated for determination of the enantiomeric purity of fourteen new chiral derivatives of xanthones (CDXs). The separations were performed with the CSPs Chirobiotic T, Chirobiotic TAG, Chirobiotic V and Chirobiotic R under multimodal elution conditions (normal-phase, reversed-phase and polar ionic mode). The analyses were performed at room temperature in isocratic mode and UV and CD detection at a wavelength of 254nm. The best enantioselectivity and resolution were achieved on Chirobiotic R and Chirobiotic T CSPs, under normal elution conditions, with R S ranging from 1.25 to 2.50 and from 0.78 to 2.06, respectively. The optimized chromatographic conditions allowed the determination of the enantiomeric ratio of eight CDXs, always higher than 99%. In order to better understand the chromatographic behavior at a molecular level, and the structural features associated with the chiral recognition mechanism, computational studies by molecular docking were carried out using VDock. These studies shed light on the mechanisms involved in the enantioseparation for this important class of chiral compounds.
Source:Journal of Chromatography A, Volume 1241
Carla Fernandes, Maria Elizabeth Tiritan, Quezia Cass, Visvaldas Kairys, Miguel Xavier Fernandes, Madalena Pinto
A chiral HPLC method using four macrocyclic antibiotic chiral stationary phases (CSPs) has been investigated for determination of the enantiomeric purity of fourteen new chiral derivatives of xanthones (CDXs). The separations were performed with the CSPs Chirobiotic T, Chirobiotic TAG, Chirobiotic V and Chirobiotic R under multimodal elution conditions (normal-phase, reversed-phase and polar ionic mode). The analyses were performed at room temperature in isocratic mode and UV and CD detection at a wavelength of 254nm. The best enantioselectivity and resolution were achieved on Chirobiotic R and Chirobiotic T CSPs, under normal elution conditions, with R S ranging from 1.25 to 2.50 and from 0.78 to 2.06, respectively. The optimized chromatographic conditions allowed the determination of the enantiomeric ratio of eight CDXs, always higher than 99%. In order to better understand the chromatographic behavior at a molecular level, and the structural features associated with the chiral recognition mechanism, computational studies by molecular docking were carried out using VDock. These studies shed light on the mechanisms involved in the enantioseparation for this important class of chiral compounds.
The obstruction factor in size-exclusion chromatography. 2. The interparticle, intraparticle, and total obstruction factors
14 May 2012,
23:16:24
Publication year:
2012
Source:Journal of Chromatography A, Volume 1241
Dustin J. Richard, André M. Striegel
“Obstruction factor” is a generic rubric under which are usually gathered the interparticle, intraparticle, stationary phase, and total obstruction factors, γ e , γ p , γ s , and γ t , respectively. These, in turn, affect longitudinal diffusion and stationary, mobile phase, and stagnant mobile phase mass transfer. We conclude here our investigation into the various obstruction factors operative in size-exclusion chromatography (SEC). Stop-flow experiments were employed to determine either the interparticle (for analytes with K SEC =0) or the total (for analytes with K SEC >0) obstruction factor, and these results were combined with those from variable-flow-rate experiments which provided the intraparticle obstruction factor. Because of minimal enthalpic interactions between the analytes and stationary phase, in SEC γ s ≈0, which allows for isolation of the other obstruction factors. A relationship between γ t , γ e , and γ p was proposed for SEC, based on previous independent work and dependent upon the various column porosities. This relationship was extended to hydrodynamic chromatography, a technique in which, ideally, both γ s and γ p are equal to zero.
Source:Journal of Chromatography A, Volume 1241
Dustin J. Richard, André M. Striegel
“Obstruction factor” is a generic rubric under which are usually gathered the interparticle, intraparticle, stationary phase, and total obstruction factors, γ e , γ p , γ s , and γ t , respectively. These, in turn, affect longitudinal diffusion and stationary, mobile phase, and stagnant mobile phase mass transfer. We conclude here our investigation into the various obstruction factors operative in size-exclusion chromatography (SEC). Stop-flow experiments were employed to determine either the interparticle (for analytes with K SEC =0) or the total (for analytes with K SEC >0) obstruction factor, and these results were combined with those from variable-flow-rate experiments which provided the intraparticle obstruction factor. Because of minimal enthalpic interactions between the analytes and stationary phase, in SEC γ s ≈0, which allows for isolation of the other obstruction factors. A relationship between γ t , γ e , and γ p was proposed for SEC, based on previous independent work and dependent upon the various column porosities. This relationship was extended to hydrodynamic chromatography, a technique in which, ideally, both γ s and γ p are equal to zero.
Gas–liquid chromatography-obtained differences in the dissolution enthalpy between two positional isomers in a polar stationary phase: A measure of the inter- or intramolecular hydrogen bond energy?
14 May 2012,
23:16:24
Publication year:
2012
Source:Journal of Chromatography A, Volume 1241
Evgenii E. Fedorov, Oleg E. Makarov, Alexei N. Pankratov, Vyacheslav S. Grinev
Previous GLC work with several 2- and 4-substituted phenols and anilines, as well as with a pyrrolizidine alcohol, had determined the difference between the heats of dissolution of two positional isomers in a strong polar stationary liquid phase; one of these isomers forms an intramolecular hydrogen bond (intra-HB) and the other has no such bond for steric reasons. The energies of the intermolecular hydrogen bonds (inter-HBs), ΔH inter-HB, formed by the 1,2- and 1,4-isomers with the molecules of a polar phase had been assumed approximately equal, so the difference between them could be ignored. The same assumption had been made for the energies of nonspecific interactions (NSIs), ΔH NSI. It had been concluded that the found difference can be considered as an intra-HB energy (enthalpy), ΔH intra-HB, when the energies (enthalpies) of inter-HBs formed by the 1,2- and 1,4-isomers under study with the molecules of a polar phase are much greater in absolute value than ΔH intra-HB. And, conversely, when |ΔH intra-HB|>|ΔH inter-HB|, an inter-HB enthalpy will result. With the same assumptions, we here obtained an extended thermodynamic equation and corrected this above conclusion on the basis of a general consideration of the dissolution thermodynamics for two isomers of a molecule in a polar phase. Account was taken of the coefficients of isomer partitioning between the liquid and the gaseous phase at the experimental temperature. The conclusion made previously was adjusted for ΔH NSI and formulated as follows: The GLC method determines the intra-HB energy at |ΔH intra-HB|≤|ΔH inter-HB +ΔH NSI|. If |ΔH intra-HB|>|ΔH inter-HB +ΔH NSI|, the method yields the values of ΔH inter-HB +ΔH NSI. This new conclusion was illustrated with virtual (numerical) experiments in which various ΔH intra-HB, ΔH inter-HB, and ΔH NSI values were postulated and results were obtained that would have been achieved by GLC if it had been done. Using a capillary column with the PEG 20M stationary phase, we measured the differences between the heats of dissolution for six pairs of isomers of phenolic compounds and for seven pairs of disubstituted benzene derivatives, which have similar structures but cannot form an intra-HB. The benzene derivatives served to make an approximate experimental estimate of the difference between the energies of NSIs of the isomers under study with a polar phase, ΔH NSI.
Source:Journal of Chromatography A, Volume 1241
Evgenii E. Fedorov, Oleg E. Makarov, Alexei N. Pankratov, Vyacheslav S. Grinev
Previous GLC work with several 2- and 4-substituted phenols and anilines, as well as with a pyrrolizidine alcohol, had determined the difference between the heats of dissolution of two positional isomers in a strong polar stationary liquid phase; one of these isomers forms an intramolecular hydrogen bond (intra-HB) and the other has no such bond for steric reasons. The energies of the intermolecular hydrogen bonds (inter-HBs), ΔH inter-HB, formed by the 1,2- and 1,4-isomers with the molecules of a polar phase had been assumed approximately equal, so the difference between them could be ignored. The same assumption had been made for the energies of nonspecific interactions (NSIs), ΔH NSI. It had been concluded that the found difference can be considered as an intra-HB energy (enthalpy), ΔH intra-HB, when the energies (enthalpies) of inter-HBs formed by the 1,2- and 1,4-isomers under study with the molecules of a polar phase are much greater in absolute value than ΔH intra-HB. And, conversely, when |ΔH intra-HB|>|ΔH inter-HB|, an inter-HB enthalpy will result. With the same assumptions, we here obtained an extended thermodynamic equation and corrected this above conclusion on the basis of a general consideration of the dissolution thermodynamics for two isomers of a molecule in a polar phase. Account was taken of the coefficients of isomer partitioning between the liquid and the gaseous phase at the experimental temperature. The conclusion made previously was adjusted for ΔH NSI and formulated as follows: The GLC method determines the intra-HB energy at |ΔH intra-HB|≤|ΔH inter-HB +ΔH NSI|. If |ΔH intra-HB|>|ΔH inter-HB +ΔH NSI|, the method yields the values of ΔH inter-HB +ΔH NSI. This new conclusion was illustrated with virtual (numerical) experiments in which various ΔH intra-HB, ΔH inter-HB, and ΔH NSI values were postulated and results were obtained that would have been achieved by GLC if it had been done. Using a capillary column with the PEG 20M stationary phase, we measured the differences between the heats of dissolution for six pairs of isomers of phenolic compounds and for seven pairs of disubstituted benzene derivatives, which have similar structures but cannot form an intra-HB. The benzene derivatives served to make an approximate experimental estimate of the difference between the energies of NSIs of the isomers under study with a polar phase, ΔH NSI.
Gas chromatography coupled to mass spectrometry analysis of volatiles, sugars, organic acids and aminoacids in Valencia Late orange juice and reliability of the Automated Mass Spectral Deconvolution and Identification System for their automatic identification and quantification
14 May 2012,
23:16:24
Publication year:
2012
Source:Journal of Chromatography A, Volume 1241
Manuela Cerdán-Calero, José María Sendra, Enrique Sentandreu
Neutral volatiles and non-volatile polar compounds (sugars, organics acids and aminoacids) present in Valencia Late orange juice have been analysed by Gas Chromatography coupled to Mass Spectrometry (GC–MS). Before analysis, the neutral volatiles have been extracted by Headspace-Solid Phase Microextraction (HS-SPME), and the non-volatile polar compounds have been transformed to their corresponding volatile trimethylsilyl (TMS) derivatives. From the resulting raw GC–MS data files, the reliability of the Automated Mass Spectral Deconvolution and Identification System (AMDIS) to perform accurate identification and quantification of the compounds present in the sample has been tested. Hence, both raw GC–MS data files have been processed automatically by using AMDIS and manually by using Xcalibur™, the manufacturer's data processing software for the GC–MS platform used. Results indicate that the reliability of AMDIS for accurate identification and quantification of the compounds present in the sample strongly depends on a number of operational settings, for both the MS and AMDIS, which must be optimized for the particular type of assayed sample. After optimization of these settings, AMDIS and Xcalibur™ yield practically the same results. A total of 85 volatiles and 22 polar compounds have been identified and quantified in Valencia Late orange juice.
Source:Journal of Chromatography A, Volume 1241
Manuela Cerdán-Calero, José María Sendra, Enrique Sentandreu
Neutral volatiles and non-volatile polar compounds (sugars, organics acids and aminoacids) present in Valencia Late orange juice have been analysed by Gas Chromatography coupled to Mass Spectrometry (GC–MS). Before analysis, the neutral volatiles have been extracted by Headspace-Solid Phase Microextraction (HS-SPME), and the non-volatile polar compounds have been transformed to their corresponding volatile trimethylsilyl (TMS) derivatives. From the resulting raw GC–MS data files, the reliability of the Automated Mass Spectral Deconvolution and Identification System (AMDIS) to perform accurate identification and quantification of the compounds present in the sample has been tested. Hence, both raw GC–MS data files have been processed automatically by using AMDIS and manually by using Xcalibur™, the manufacturer's data processing software for the GC–MS platform used. Results indicate that the reliability of AMDIS for accurate identification and quantification of the compounds present in the sample strongly depends on a number of operational settings, for both the MS and AMDIS, which must be optimized for the particular type of assayed sample. After optimization of these settings, AMDIS and Xcalibur™ yield practically the same results. A total of 85 volatiles and 22 polar compounds have been identified and quantified in Valencia Late orange juice.
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