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Selected papers from the latest issue:
Hollow-fiber liquid-phase microextraction of amphetamine-type stimulants in human hair samples
20 August 2012,
11:28:59
Publication year:
2012
Source:Journal of Chromatography A, Volume 1254
Lorena do Nascimento Pantaleão, Beatriz Aparecida Passos Bismara Paranhos, Mauricio Yonamine
A fast method was optimized and validated in order to quantify amphetamine-type stimulants (amphetamine, AMP; methamphetamine, MAMP; fenproporex, FPX; 3,4-methylenedioxymethamphetamine, MDMA; and 3,4-methylenedioxyamphetamine, MDA) in human hair samples. The method was based in an initial procedure of decontamination of hair samples (50mg) with dichloromethane, followed by alkaline hydrolysis and extraction of the amphetamines using hollow-fiber liquid-phase micro extraction (HF-LPME) in the three-phase mode. Gas chromatography–mass spectrometry (GC–MS) was used for identification and quantification of the analytes. The LoQs obtained for all amphetamines (around 0.05ng/mg) were below the cut-off value (0.2ng/mg) established by the Society of Hair Testing (SoHT). The method showed to be simple and precise. The intra-day and inter-day precisions were within 10.6% and 11.4%, respectively, with the use of only two deuterated internal standards (AMP-d5 and MDMA-d5). By using the weighted least squares linear regression (1/x 2), the accuracy of the method was satisfied in the lower concentration levels (accuracy values better than 87%). Hair samples collected from six volunteers who reported regular use of amphetamines were submitted to the developed method. Drug detection was observed in all samples of the volunteers.
Source:Journal of Chromatography A, Volume 1254
Lorena do Nascimento Pantaleão, Beatriz Aparecida Passos Bismara Paranhos, Mauricio Yonamine
A fast method was optimized and validated in order to quantify amphetamine-type stimulants (amphetamine, AMP; methamphetamine, MAMP; fenproporex, FPX; 3,4-methylenedioxymethamphetamine, MDMA; and 3,4-methylenedioxyamphetamine, MDA) in human hair samples. The method was based in an initial procedure of decontamination of hair samples (50mg) with dichloromethane, followed by alkaline hydrolysis and extraction of the amphetamines using hollow-fiber liquid-phase micro extraction (HF-LPME) in the three-phase mode. Gas chromatography–mass spectrometry (GC–MS) was used for identification and quantification of the analytes. The LoQs obtained for all amphetamines (around 0.05ng/mg) were below the cut-off value (0.2ng/mg) established by the Society of Hair Testing (SoHT). The method showed to be simple and precise. The intra-day and inter-day precisions were within 10.6% and 11.4%, respectively, with the use of only two deuterated internal standards (AMP-d5 and MDMA-d5). By using the weighted least squares linear regression (1/x 2), the accuracy of the method was satisfied in the lower concentration levels (accuracy values better than 87%). Hair samples collected from six volunteers who reported regular use of amphetamines were submitted to the developed method. Drug detection was observed in all samples of the volunteers.
Highlights
► This is the first study that reported the determination of amphetamines in hair samples by means of HF-LPME. ► Little volume of organic solvent is required for sample preparation. ► This paper provided data for the analysis of fenproporex in real human hair samples.Hydrophilic immobilized trypsin reactor with magnetic graphene oxide as support for high efficient proteome digestion
20 August 2012,
11:28:59
Publication year:
2012
Source:Journal of Chromatography A, Volume 1254
Bo Jiang, Kaiguang Yang, Qun Zhao, Qi Wu, Zhen Liang, Lihua Zhang, Xiaojun Peng, Yukui Zhang
In this paper, magnetic Fe3O4 nanoparticles modified graphene oxide nanocomposites (GO–CO–NH–Fe3O4) were prepared by covalent bonding, via the reaction between the amino groups of fuctionalized Fe3O4 and the carboxylic groups of GO, confirmed by Fourier-transform infrared spectra, Raman spectroscopy, and transmission electron microscopy. With GO–CO–NH–Fe3O4 as a novel substrate, trypsin was immobilized via π–π stacking and hydrogen bonding interaction, and the binding capacity of trypsin reached as high as 0.275mg/mg. Since GO–CO–NH–Fe3O4 worked as not only support for enzyme immobilization, but also as an excellent microwave irradiation absorber, the digestion efficiency could be further improved with microwave assistance. By such an immobilized enzymatic reactor (IMER), standard proteins could be efficiently digested within 15s, with sequence coverages comparable or better than those obtained by conventional in-solution digestion (12h). Since trypsin was immobilized under mild conditions, the enzymatic activity of IMER preserved at least for a month. In addition, due to the good hydrophilicity of GO, no peptide residue was observed in the sequent digestion of bovine serum albumin and myoglobin. To further confirm the efficiency of such an IMER for proteome analysis, it was applied to digest proteins extracted from rat liver, followed by nanoRPLC–ESI-MS/MS analysis. With only 5min microwave-assisted digestion, in 3 parallel runs, totally 456 protein groups were identified, comparable to that obtained by 12h in-solution digestion, indicating the great potential of IMERs with GO–CO–NH–Fe3O4 as the support for high throughput proteome study.
Source:Journal of Chromatography A, Volume 1254
Bo Jiang, Kaiguang Yang, Qun Zhao, Qi Wu, Zhen Liang, Lihua Zhang, Xiaojun Peng, Yukui Zhang
In this paper, magnetic Fe3O4 nanoparticles modified graphene oxide nanocomposites (GO–CO–NH–Fe3O4) were prepared by covalent bonding, via the reaction between the amino groups of fuctionalized Fe3O4 and the carboxylic groups of GO, confirmed by Fourier-transform infrared spectra, Raman spectroscopy, and transmission electron microscopy. With GO–CO–NH–Fe3O4 as a novel substrate, trypsin was immobilized via π–π stacking and hydrogen bonding interaction, and the binding capacity of trypsin reached as high as 0.275mg/mg. Since GO–CO–NH–Fe3O4 worked as not only support for enzyme immobilization, but also as an excellent microwave irradiation absorber, the digestion efficiency could be further improved with microwave assistance. By such an immobilized enzymatic reactor (IMER), standard proteins could be efficiently digested within 15s, with sequence coverages comparable or better than those obtained by conventional in-solution digestion (12h). Since trypsin was immobilized under mild conditions, the enzymatic activity of IMER preserved at least for a month. In addition, due to the good hydrophilicity of GO, no peptide residue was observed in the sequent digestion of bovine serum albumin and myoglobin. To further confirm the efficiency of such an IMER for proteome analysis, it was applied to digest proteins extracted from rat liver, followed by nanoRPLC–ESI-MS/MS analysis. With only 5min microwave-assisted digestion, in 3 parallel runs, totally 456 protein groups were identified, comparable to that obtained by 12h in-solution digestion, indicating the great potential of IMERs with GO–CO–NH–Fe3O4 as the support for high throughput proteome study.
Highlights
► GO–CO–NH–Fe3O4 nanocomposites were prepared by a facile covalent bonding. ► GO–CO–NH–Fe3O4 nanocomposites were used as trypsin immobilization substrate. ► Such an IMER showed advantages of high efficiency and low residue. ► Such an IMER was successfully applied to the digestion of rat liver samples.Innovative microwave-assisted oximation and silylation procedures for metabolomic analysis of plasma samples using gas chromatography–mass spectrometry
20 August 2012,
11:28:59
Publication year:
2012
Source:Journal of Chromatography A, Volume 1254
Zhanying Hong, Zebin Lin, Yue Liu, Guangguo Tan, Ziyang Lou, Zhenyu Zhu, Yifeng Chai, Guorong Fan, Junping Zhang, Liming Zhang
Analysis of plasma metabolomic samples by gas chromatography–mass spectrometry always requires comprehensive pretreatment including oximation and silylation. Although heating block (HB) is a commonly used method, it is time consuming. This study describes an extremely time-effective microwave-assisted (MA) oximation and silylation approach for metabolomic study of plasma samples. The Box–Behnken design was employed to optimize the MA conditions by means of oximation at 65W for 100s and then silylation through 180s incubation with 230W microwave irradiation. The results showed that microwave irradiation decreased the sample preparation time from approximately 180min to 5min without loss of information for the metabolites in plasma samples. Both the HB method and the developed MA method were applied in plasma metabolomic study of sulfur mustard intoxication. Partial least-squares discriminant analysis (PLS-DA) was used to globally understand the metabolic changes, and multi-criteria assessment was used to select the most significant and reliable variables as potential biomarkers. The data obtained by the MA method were in good correlation with the HB method. Compared with HB method, the newly developed MA oximation and silylation of plasma metabolome samples was more efficient and time-effective and may prove to be an attractive alternative for high-throughput sample preparation in plasma metabolomics.
Source:Journal of Chromatography A, Volume 1254
Zhanying Hong, Zebin Lin, Yue Liu, Guangguo Tan, Ziyang Lou, Zhenyu Zhu, Yifeng Chai, Guorong Fan, Junping Zhang, Liming Zhang
Analysis of plasma metabolomic samples by gas chromatography–mass spectrometry always requires comprehensive pretreatment including oximation and silylation. Although heating block (HB) is a commonly used method, it is time consuming. This study describes an extremely time-effective microwave-assisted (MA) oximation and silylation approach for metabolomic study of plasma samples. The Box–Behnken design was employed to optimize the MA conditions by means of oximation at 65W for 100s and then silylation through 180s incubation with 230W microwave irradiation. The results showed that microwave irradiation decreased the sample preparation time from approximately 180min to 5min without loss of information for the metabolites in plasma samples. Both the HB method and the developed MA method were applied in plasma metabolomic study of sulfur mustard intoxication. Partial least-squares discriminant analysis (PLS-DA) was used to globally understand the metabolic changes, and multi-criteria assessment was used to select the most significant and reliable variables as potential biomarkers. The data obtained by the MA method were in good correlation with the HB method. Compared with HB method, the newly developed MA oximation and silylation of plasma metabolome samples was more efficient and time-effective and may prove to be an attractive alternative for high-throughput sample preparation in plasma metabolomics.
Highlights
► Microwave-assisted oximation and silylation for plasma metabolomic was conducted. ► Box–Behnken design was employed to optimize the microwave-assisted conditions. ► Metabolomic approach was used to discover the sulfur mustard intoxication biomarkers. ► The optimized microwave-assisted method improved the time efficiency about 36 times.Magnetic retrieval of ionic liquids: Fast dispersive liquid–liquid microextraction for the determination of benzoylurea insecticides in environmental water samples
20 August 2012,
11:28:59
Publication year:
2012
Source:Journal of Chromatography A, Volume 1254
Jiaheng Zhang, Min Li, Miyi Yang, Bing Peng, Yubo Li, Wenfeng Zhou, Haixiang Gao, Runhua Lu
A novel, rapid ionic liquid dispersive liquid–liquid microextraction (IL-DLLME) technique combined with magnetic retrieval (MR-IL-DLLME) has been developed and used to analyze five benzoylurea insecticides (BUs) in environmental water samples. This procedure was based on the magnetic retrieval of the ionic liquid using unmodified magnetic nanoparticles (MNPs). In this experiment, the fine ionic liquid droplets formed in aqueous samples functioned as an extractant for the extraction of BUs; after the extraction process was completed, Fe3O4 MNPs were added as a carrier to retrieve and separate the ionic liquid from the sample solution. After the supernatant was removed, the ionic liquid was desorbed using acetonitrile and subsequently injected directly into an HPLC system for analysis. The optimum experimental parameters are as follows: 20mg of Fe3O4 (20nm) as magnetic sorbents; 70μL of [C6MIM][PF6] as the extraction solvent; 300μL of acetonitrile as the disperser solvent; a vortex extraction time of 90s with the vortex agitator set at 2800rpm and no ionic strength. Under the optimized conditions, good linearity was obtained with correlation coefficients (r) greater than 0.9981. The repeatability and reproducibility of the proposed method were found to be good, and the limits of detection ranged from 0.05μgL−1 to 0.15μgL−1. The proposed method was then successfully used for the rapid determination of BUs in real water samples. The recoveries of five BUs at two spiked levels ranged from 79.8 to 91.7% with RSDs less than 6.0%.
Source:Journal of Chromatography A, Volume 1254
Jiaheng Zhang, Min Li, Miyi Yang, Bing Peng, Yubo Li, Wenfeng Zhou, Haixiang Gao, Runhua Lu
A novel, rapid ionic liquid dispersive liquid–liquid microextraction (IL-DLLME) technique combined with magnetic retrieval (MR-IL-DLLME) has been developed and used to analyze five benzoylurea insecticides (BUs) in environmental water samples. This procedure was based on the magnetic retrieval of the ionic liquid using unmodified magnetic nanoparticles (MNPs). In this experiment, the fine ionic liquid droplets formed in aqueous samples functioned as an extractant for the extraction of BUs; after the extraction process was completed, Fe3O4 MNPs were added as a carrier to retrieve and separate the ionic liquid from the sample solution. After the supernatant was removed, the ionic liquid was desorbed using acetonitrile and subsequently injected directly into an HPLC system for analysis. The optimum experimental parameters are as follows: 20mg of Fe3O4 (20nm) as magnetic sorbents; 70μL of [C6MIM][PF6] as the extraction solvent; 300μL of acetonitrile as the disperser solvent; a vortex extraction time of 90s with the vortex agitator set at 2800rpm and no ionic strength. Under the optimized conditions, good linearity was obtained with correlation coefficients (r) greater than 0.9981. The repeatability and reproducibility of the proposed method were found to be good, and the limits of detection ranged from 0.05μgL−1 to 0.15μgL−1. The proposed method was then successfully used for the rapid determination of BUs in real water samples. The recoveries of five BUs at two spiked levels ranged from 79.8 to 91.7% with RSDs less than 6.0%.
Highlights
► A novel approach (MR-IL-DLLME) was developed. ► [C6MIM][PF6] was chosen as extractant and absorbed by Fe3O4 magnetic nanoparticles. ► The method exceptionally accelerates the sample preparation, extraction was completed within 5min. ► The method was applied for benzoylurea insecticides in real water samples.Overload behavior and apparent efficiencies in chromatography
20 August 2012,
11:28:59
Publication year:
2012
Source:Journal of Chromatography A, Volume 1254
Fabrice Gritti, Georges Guiochon
Over the last 50 years, many analysts have attempted to analyze column overloading by measuring the drop of the column HETP with increasing sample size and to predict elution band profiles from overloaded columns by combining the influences of the thermodynamic overloading and of axial dispersion, using a simplistic perturbation model. This approach violates the principle of mass conservation. The results of the predictions do not agree with those of exact calculations made with the equilibrium-dispersive (ED) model of chromatography for constant axial dispersion. The plots of the reduced apparent column efficiency N/N kin , versus the injected concentration, log C 0, or the injected mass, log m 0, may provide useful information only regarding the onset of overloading of any particular column but they are meaningless to compare the overloading behavior of columns packed with different packing materials, unless the columns used satisfy impractical requirements (same efficiency, same retention factors, and sample sizes used proportional to the volume of stationary phase in the column).
Source:Journal of Chromatography A, Volume 1254
Fabrice Gritti, Georges Guiochon
Over the last 50 years, many analysts have attempted to analyze column overloading by measuring the drop of the column HETP with increasing sample size and to predict elution band profiles from overloaded columns by combining the influences of the thermodynamic overloading and of axial dispersion, using a simplistic perturbation model. This approach violates the principle of mass conservation. The results of the predictions do not agree with those of exact calculations made with the equilibrium-dispersive (ED) model of chromatography for constant axial dispersion. The plots of the reduced apparent column efficiency N/N kin , versus the injected concentration, log C 0, or the injected mass, log m 0, may provide useful information only regarding the onset of overloading of any particular column but they are meaningless to compare the overloading behavior of columns packed with different packing materials, unless the columns used satisfy impractical requirements (same efficiency, same retention factors, and sample sizes used proportional to the volume of stationary phase in the column).
Highlights
► Elution band profiles change shape progressively when the sample size is increased. ► A dispersive convolution of a thermodynamic profile may model the evolution of these profiles. ► The sum of the band variances of these two terms does not provide the variance of the elution profile. ► Because in nonlinear chromatography, these two variances are not additive. ► Only knowledge of the adsorbent saturation capacity informs on the degree of column overloading.More accurate matrix-matched quantification using standard superposition method for herbal medicines
20 August 2012,
11:28:59
Publication year:
2012
Source:Journal of Chromatography A, Volume 1254
Ying Liu, Xiao-Wei Shi, E-Hu Liu, Long-Sheng Sheng, Lian-Wen Qi, Ping Li
Various analytical technologies have been developed for quantitative determination of marker compounds in herbal medicines (HMs). One important issue is matrix effects that must be addressed in method validation for different detections. Unlike biological fluids, blank matrix samples for calibration are usually unavailable for HMs. In this work, practical approaches for minimizing matrix effects in HMs analysis were proposed. The matrix effects in quantitative analysis of five saponins from Panax notoginseng were assessed using high-performance liquid chromatography (HPLC). Matrix components were found to interfere with the ionization of target analytes when mass spectrometry (MS) detection were employed. To compensate the matrix signal suppression/enhancement, two matrix-matched methods, standard addition method with the target-knockout extract and standard superposition method with a HM extract were developed and tested in this work. The results showed that the standard superposition method is simple and practical for overcoming matrix effects for quantitative analysis of HMs. Moreover, the interference components were observed to interfere with light scattering of target analytes when evaporative light scattering detection (ELSD) was utilized for quantitative analysis of HMs but was not indicated when Ultraviolet detection (UV) were employed. Thus, the issue of interference effects should be addressed and minimized for quantitative HPLC–ELSD and HPLC–MS methodologies for quality control of HMs.
Source:Journal of Chromatography A, Volume 1254
Ying Liu, Xiao-Wei Shi, E-Hu Liu, Long-Sheng Sheng, Lian-Wen Qi, Ping Li
Various analytical technologies have been developed for quantitative determination of marker compounds in herbal medicines (HMs). One important issue is matrix effects that must be addressed in method validation for different detections. Unlike biological fluids, blank matrix samples for calibration are usually unavailable for HMs. In this work, practical approaches for minimizing matrix effects in HMs analysis were proposed. The matrix effects in quantitative analysis of five saponins from Panax notoginseng were assessed using high-performance liquid chromatography (HPLC). Matrix components were found to interfere with the ionization of target analytes when mass spectrometry (MS) detection were employed. To compensate the matrix signal suppression/enhancement, two matrix-matched methods, standard addition method with the target-knockout extract and standard superposition method with a HM extract were developed and tested in this work. The results showed that the standard superposition method is simple and practical for overcoming matrix effects for quantitative analysis of HMs. Moreover, the interference components were observed to interfere with light scattering of target analytes when evaporative light scattering detection (ELSD) was utilized for quantitative analysis of HMs but was not indicated when Ultraviolet detection (UV) were employed. Thus, the issue of interference effects should be addressed and minimized for quantitative HPLC–ELSD and HPLC–MS methodologies for quality control of HMs.
Highlights
► Accurate quantification is important for quality control of herbal medicines. ► Blank matrix sample is usually unavailable for herbal medicines. ► Standard superposition method was developed for quantitative determination for HMs. ► Matrix components interfered with the ionization and light scattering of analytes. ► Standard superposition method is simple and practical for overcoming matrix effects.Effect of background correction on peak detection and quantification in online comprehensive two-dimensional liquid chromatography using diode array detection
20 August 2012,
11:28:59
Publication year:
2012
Source:Journal of Chromatography A, Volume 1254
Robert C. Allen, Mallory G. John, Sarah C. Rutan, Marcelo R. Filgueira, Peter W. Carr
A singular value decomposition-based background correction (SVD-BC) technique is proposed for the reduction of background contributions in online comprehensive two-dimensional liquid chromatography (LC×LC) data. The SVD-BC technique was compared to simply subtracting a blank chromatogram from a sample chromatogram and to a previously reported background correction technique for one dimensional chromatography, which uses an asymmetric weighted least squares (AWLS) approach. AWLS was the only background correction technique to completely remove the background artifacts from the samples as evaluated by visual inspection. However, the SVD-BC technique greatly reduced or eliminated the background artifacts as well and preserved the peak intensity better than AWLS. The loss in peak intensity by AWLS resulted in lower peak counts at the detection thresholds established using standards samples. However, the SVD-BC technique was found to introduce noise which led to detection of false peaks at the lower detection thresholds. As a result, the AWLS technique gave more precise peak counts than the SVD-BC technique, particularly at the lower detection thresholds. While the AWLS technique resulted in more consistent percent residual standard deviation values, a statistical improvement in peak quantification after background correction was not found regardless of the background correction technique used.
Source:Journal of Chromatography A, Volume 1254
Robert C. Allen, Mallory G. John, Sarah C. Rutan, Marcelo R. Filgueira, Peter W. Carr
A singular value decomposition-based background correction (SVD-BC) technique is proposed for the reduction of background contributions in online comprehensive two-dimensional liquid chromatography (LC×LC) data. The SVD-BC technique was compared to simply subtracting a blank chromatogram from a sample chromatogram and to a previously reported background correction technique for one dimensional chromatography, which uses an asymmetric weighted least squares (AWLS) approach. AWLS was the only background correction technique to completely remove the background artifacts from the samples as evaluated by visual inspection. However, the SVD-BC technique greatly reduced or eliminated the background artifacts as well and preserved the peak intensity better than AWLS. The loss in peak intensity by AWLS resulted in lower peak counts at the detection thresholds established using standards samples. However, the SVD-BC technique was found to introduce noise which led to detection of false peaks at the lower detection thresholds. As a result, the AWLS technique gave more precise peak counts than the SVD-BC technique, particularly at the lower detection thresholds. While the AWLS technique resulted in more consistent percent residual standard deviation values, a statistical improvement in peak quantification after background correction was not found regardless of the background correction technique used.
Highlights
► We compare three background correction techniques for LC×LC-DAD data. ► We compare two peak detection methods for LC×LC-DAD data after background correction. ► The AWLS technique was the only technique to completely remove the background artifacts. ► The derivative based detection approach detected more peaks than the drain algorithm. ► A significant improvement in quantification was not found after background correction.Evaporative light scattering detector in normal-phase high-performance liquid chromatography determination of FAME oxidation products
20 August 2012,
11:28:59
Publication year:
2012
Source:Journal of Chromatography A, Volume 1254
Arturo Morales, Susana Marmesat, M. Carmen Dobarganes, Gloria Márquez-Ruiz, Joaquín Velasco
The use of an ELS detector in NP-HPLC for quantitative analysis of oxidation products in FAME obtained from oils is evaluated in this study. The results obtained have shown that the ELS detector enables the quantitative determination of the hydroperoxides of oleic and linoleic acid methyl esters as a whole, and connected in series with a UV detector makes it possible to determine both groups of compounds by difference, providing useful complementary information. The limits of detection (LOD) and quantification (LOQ) found for hydroperoxides were respectively 2.5 and 5.7μgmL−1 and precision of quantitation expressed as coefficient of variation was lower than 10%. Due to a low sensitivity the ELS detector shows limitations to determine the low contents of secondary oxidation products in the direct analysis of FAME oxidized at low or moderate temperature. Analysis of FAME samples obtained either from high linoleic sunflower oil (HLSO) or high oleic sunflower oil (HOSO) and oxidized at 80°C showed that only ketodienes formed from methyl linoleate can be determined in samples with relatively high oxidation, being the LOD and LOQ 0.2 and 0.4mg/g FAME, respectively, at the analytical conditions applied. The ELS detector also enabled the determination of methyl cis-9,10-epoxystearate and methyl trans-9,10-epoxystearate, which were resolved at the chromatographic conditions applied. Results showed that these compounds, which are formed from methyl oleate, were not detected in the high-linoleic sample, but occurred at non-negligible levels in the oxidized FAME obtained from HOSO.
Source:Journal of Chromatography A, Volume 1254
Arturo Morales, Susana Marmesat, M. Carmen Dobarganes, Gloria Márquez-Ruiz, Joaquín Velasco
The use of an ELS detector in NP-HPLC for quantitative analysis of oxidation products in FAME obtained from oils is evaluated in this study. The results obtained have shown that the ELS detector enables the quantitative determination of the hydroperoxides of oleic and linoleic acid methyl esters as a whole, and connected in series with a UV detector makes it possible to determine both groups of compounds by difference, providing useful complementary information. The limits of detection (LOD) and quantification (LOQ) found for hydroperoxides were respectively 2.5 and 5.7μgmL−1 and precision of quantitation expressed as coefficient of variation was lower than 10%. Due to a low sensitivity the ELS detector shows limitations to determine the low contents of secondary oxidation products in the direct analysis of FAME oxidized at low or moderate temperature. Analysis of FAME samples obtained either from high linoleic sunflower oil (HLSO) or high oleic sunflower oil (HOSO) and oxidized at 80°C showed that only ketodienes formed from methyl linoleate can be determined in samples with relatively high oxidation, being the LOD and LOQ 0.2 and 0.4mg/g FAME, respectively, at the analytical conditions applied. The ELS detector also enabled the determination of methyl cis-9,10-epoxystearate and methyl trans-9,10-epoxystearate, which were resolved at the chromatographic conditions applied. Results showed that these compounds, which are formed from methyl oleate, were not detected in the high-linoleic sample, but occurred at non-negligible levels in the oxidized FAME obtained from HOSO.
Highlights
► Coupling of ELS in NP-HPLC–UV provides useful complementary analytical information in the analysis of FAME oxidation products. ► Quantitative analysis of hydroperoxides of linoleic and oleic acid in oxidized samples of FAME. ► Quantitative analysis of monoepoxides formed from oleic acid methyl ester by NP-HPLC-ELS. ► Formation of monoepoxides at moderate temperature (80°C) at levels of mg/g in FAME derived from monounsaturated oils. ► Detection of monoepoxides in lipids is an indication of significant oxidation of oleic acid.On influence of sample loading conditions on peak shape and separation efficiency in preparative isocratic counter-current chromatography
20 August 2012,
11:28:59
Publication year:
2012
Source:Journal of Chromatography A, Volume 1254
Artak E. Kostanyan
The cell model theory of CCC is extended to develop analytical solutions for various sample loading conditions (non-impulse loading with separate feed stream and with the mobile phase flow, impulse and non-impulse periodic loading). Equations are presented allowing the simulation of the chromatograms for various sample loading conditions. These equations can help to predict the influence of sample loading conditions on the separation of a given feed mixture and select a suitable compromise between the productivity and the resolution in the isocratic preparative and production CCC separations. It is shown that: when the sample loading time is about 2% of the mean residence time, the effect of loading time can be neglected; the loading time about 20% of the mean residence time seems to be quite acceptable; proper selection of the conditions for the sample loading can allow increasing the productivity by an order of magnitude ensuring, a desirable separation.
Source:Journal of Chromatography A, Volume 1254
Artak E. Kostanyan
The cell model theory of CCC is extended to develop analytical solutions for various sample loading conditions (non-impulse loading with separate feed stream and with the mobile phase flow, impulse and non-impulse periodic loading). Equations are presented allowing the simulation of the chromatograms for various sample loading conditions. These equations can help to predict the influence of sample loading conditions on the separation of a given feed mixture and select a suitable compromise between the productivity and the resolution in the isocratic preparative and production CCC separations. It is shown that: when the sample loading time is about 2% of the mean residence time, the effect of loading time can be neglected; the loading time about 20% of the mean residence time seems to be quite acceptable; proper selection of the conditions for the sample loading can allow increasing the productivity by an order of magnitude ensuring, a desirable separation.
Highlights
► Analytical solutions for various sample loading conditions have been developed. ► Equations are presented allowing the simulation of the chromatograms. ► Suitable compromise between the productivity and the resolution can be selected.Multi-residue determination of pharmaceutical and personal care products in vegetables
20 August 2012,
11:28:59
Publication year:
2012
Source:Journal of Chromatography A, Volume 1254
Xiaoqin Wu, Jeremy Landon Conkle, Jay Gan
Treated wastewater irrigation and biosolid amendment are increasingly practiced worldwide and contamination of plants, especially produces that may be consumed raw by humans, by pharmaceutical and personal care products (PPCPs), is an emerging concern. A sensitive method was developed for the simultaneous measurement of 19 frequently-occurring PPCPs in vegetables using high-performance liquid chromatography–electrospray ionization tandem mass spectrometry (HPLC–ESI–MS/MS) for detection, combined with ultrasonic extraction and solid phase extraction (SPE) cleanup for sample preparation. Deuterated standards were used as surrogates to quantify corresponding analytes. The corrected recoveries ranged between 87.1 and 123.5% for iceberg lettuce, with intra- and inter-day variations less than 20%, and the method detection limits (MDLs) in the range of 0.04–3.0ngg−1 dry weight (dw). The corrected recoveries were equally good when the method was used on celery, tomato, carrot, broccoli, bell pepper and spinach. The method was further applied to examine uptake of PPCPs by iceberg lettuce and spinach grown in hydroponic solutions containing each PPCP at 500ngL−1. Twelve PPCPs were detected in lettuce leaves with concentrations from 0.2 to 28.7ngg−1 dw, while 11 PPCPs were detected in spinach leaves at 0.04–34.0ngg−1 dw. Given the diverse chemical structures of PPCPs considered in this study, this method may be used for screening PPCP residues in vegetables and other plants impacted by treated wastewater or biosolids, and to estimate potential human exposure via dietary uptake.
Source:Journal of Chromatography A, Volume 1254
Xiaoqin Wu, Jeremy Landon Conkle, Jay Gan
Treated wastewater irrigation and biosolid amendment are increasingly practiced worldwide and contamination of plants, especially produces that may be consumed raw by humans, by pharmaceutical and personal care products (PPCPs), is an emerging concern. A sensitive method was developed for the simultaneous measurement of 19 frequently-occurring PPCPs in vegetables using high-performance liquid chromatography–electrospray ionization tandem mass spectrometry (HPLC–ESI–MS/MS) for detection, combined with ultrasonic extraction and solid phase extraction (SPE) cleanup for sample preparation. Deuterated standards were used as surrogates to quantify corresponding analytes. The corrected recoveries ranged between 87.1 and 123.5% for iceberg lettuce, with intra- and inter-day variations less than 20%, and the method detection limits (MDLs) in the range of 0.04–3.0ngg−1 dry weight (dw). The corrected recoveries were equally good when the method was used on celery, tomato, carrot, broccoli, bell pepper and spinach. The method was further applied to examine uptake of PPCPs by iceberg lettuce and spinach grown in hydroponic solutions containing each PPCP at 500ngL−1. Twelve PPCPs were detected in lettuce leaves with concentrations from 0.2 to 28.7ngg−1 dw, while 11 PPCPs were detected in spinach leaves at 0.04–34.0ngg−1 dw. Given the diverse chemical structures of PPCPs considered in this study, this method may be used for screening PPCP residues in vegetables and other plants impacted by treated wastewater or biosolids, and to estimate potential human exposure via dietary uptake.
Highlights
► We develop a method for the simultaneous measurement of 19 PPCPs in vegetables. ► The corrected recoveries are good for iceberg lettuce and the other six vegetables. ► The method detection limits are in the range of 0.04–3.0ngg−1 dw. ► Many PPCPs can be taken up by lettuce and spinach grown in hydroponic solutions.Allergic asthma exhaled breath metabolome: A challenge for comprehensive two-dimensional gas chromatography
20 August 2012,
11:28:59
Publication year:
2012
Source:Journal of Chromatography A, Volume 1254
M. Caldeira, R. Perestrelo, A.S. Barros, M.J. Bilelo, A. Morête, J.S. Câmara, S.M. Rocha
Allergic asthma represents an important public health issue, most common in the paediatric population, characterized by airway inflammation that may lead to changes in volatiles secreted via the lungs. Thus, exhaled breath has potential to be a matrix with relevant metabolomic information to characterize this disease. Progress in biochemistry, health sciences and related areas depends on instrumental advances, and a high throughput and sensitive equipment such as comprehensive two-dimensional gas chromatography–time of flight mass spectrometry (GC×GC–ToFMS) was considered. GC×GC–ToFMS application in the analysis of the exhaled breath of 32 children with allergic asthma, from which 10 had also allergic rhinitis, and 27 control children allowed the identification of several hundreds of compounds belonging to different chemical families. Multivariate analysis, using Partial Least Squares-Discriminant Analysis in tandem with Monte Carlo Cross Validation was performed to assess the predictive power and to help the interpretation of recovered compounds possibly linked to oxidative stress, inflammation processes or other cellular processes that may characterize asthma. The results suggest that the model is robust, considering the high classification rate, sensitivity, and specificity. A pattern of six compounds belonging to the alkanes characterized the asthmatic population: nonane, 2,2,4,6,6-pentamethylheptane, decane, 3,6-dimethyldecane, dodecane, and tetradecane. To explore future clinical applications, and considering the future role of molecular-based methodologies, a compound set was established to rapid access of information from exhaled breath, reducing the time of data processing, and thus, becoming more expedite method for the clinical purposes.
Source:Journal of Chromatography A, Volume 1254
M. Caldeira, R. Perestrelo, A.S. Barros, M.J. Bilelo, A. Morête, J.S. Câmara, S.M. Rocha
Allergic asthma represents an important public health issue, most common in the paediatric population, characterized by airway inflammation that may lead to changes in volatiles secreted via the lungs. Thus, exhaled breath has potential to be a matrix with relevant metabolomic information to characterize this disease. Progress in biochemistry, health sciences and related areas depends on instrumental advances, and a high throughput and sensitive equipment such as comprehensive two-dimensional gas chromatography–time of flight mass spectrometry (GC×GC–ToFMS) was considered. GC×GC–ToFMS application in the analysis of the exhaled breath of 32 children with allergic asthma, from which 10 had also allergic rhinitis, and 27 control children allowed the identification of several hundreds of compounds belonging to different chemical families. Multivariate analysis, using Partial Least Squares-Discriminant Analysis in tandem with Monte Carlo Cross Validation was performed to assess the predictive power and to help the interpretation of recovered compounds possibly linked to oxidative stress, inflammation processes or other cellular processes that may characterize asthma. The results suggest that the model is robust, considering the high classification rate, sensitivity, and specificity. A pattern of six compounds belonging to the alkanes characterized the asthmatic population: nonane, 2,2,4,6,6-pentamethylheptane, decane, 3,6-dimethyldecane, dodecane, and tetradecane. To explore future clinical applications, and considering the future role of molecular-based methodologies, a compound set was established to rapid access of information from exhaled breath, reducing the time of data processing, and thus, becoming more expedite method for the clinical purposes.
Highlights
► Exhaled breath has the potential to characterize allergic asthma. ► HS-SPME/GC×GC–ToFMS was applied in allergic asthma breath analysis. ► Hundreds of compounds were detected by the developed methodology. ► PLS-DA showed robustness, a high classification rate, sensitivity, and specificity. ► For possible clinical applications, a compound set was successfully applied.Component correlation between related samples by using comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry with chemometric tools
20 August 2012,
11:28:59
Publication year:
2012
Source:Journal of Chromatography A, Volume 1254
Zhong-Da Zeng, Helmut M. Hugel, Philip J. Marriott
A chemometric strategy has been developed to discover component difference and similarity between two chromatograms (correlation) by using comprehensive two-dimensional (2D) gas chromatography with time-of-flight mass spectrometry (GC×GC-TOFMS). It allows for rapid determination of the presence or absence of analytes of interest in both pure and overlapping peak clusters, and then locates elution windows of target components. First, representative elution windows of analytes are extracted from the 2D GC×GC map to characterize the spectral space and further construct an orthogonal projection matrix for analysis. Next, multi-component spectral correlative chromatography (MSCC) is employed to scan the whole or pre-selected GC×GC-TOFMS data range to obtain component features. An auto-correlative projection curve is proposed to assess the projection residual from MSCC by defining a new evaluation index as reference, based on fixed-size moving window evolving factor analysis. In principle, the method can also be utilized to locate specific compounds whose known spectra are available. It is not restricted by data with high homoscedastic and heteroscedastic noise. Simulated GC-MS data and an extremely complicated herbal product mixture comprising 9 herbs demonstrates that the two-dimensional correlative distribution graph is effective for chemical interpretation between GC×GC-TOFMS data. It allows discovery of information buried in this type of highly complex dataset, especially for rapid and effective data comparison, where specific molecular identity might otherwise be hidden.
Source:Journal of Chromatography A, Volume 1254
Zhong-Da Zeng, Helmut M. Hugel, Philip J. Marriott
A chemometric strategy has been developed to discover component difference and similarity between two chromatograms (correlation) by using comprehensive two-dimensional (2D) gas chromatography with time-of-flight mass spectrometry (GC×GC-TOFMS). It allows for rapid determination of the presence or absence of analytes of interest in both pure and overlapping peak clusters, and then locates elution windows of target components. First, representative elution windows of analytes are extracted from the 2D GC×GC map to characterize the spectral space and further construct an orthogonal projection matrix for analysis. Next, multi-component spectral correlative chromatography (MSCC) is employed to scan the whole or pre-selected GC×GC-TOFMS data range to obtain component features. An auto-correlative projection curve is proposed to assess the projection residual from MSCC by defining a new evaluation index as reference, based on fixed-size moving window evolving factor analysis. In principle, the method can also be utilized to locate specific compounds whose known spectra are available. It is not restricted by data with high homoscedastic and heteroscedastic noise. Simulated GC-MS data and an extremely complicated herbal product mixture comprising 9 herbs demonstrates that the two-dimensional correlative distribution graph is effective for chemical interpretation between GC×GC-TOFMS data. It allows discovery of information buried in this type of highly complex dataset, especially for rapid and effective data comparison, where specific molecular identity might otherwise be hidden.
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