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Selected papers from the latest issue:
Recent development and applications of dispersive liquid–liquid microextraction
03 June 2013,
08:31:53
Publication date: 21 June
2013
Source:Journal of Chromatography A, Volume 1295
Author(s): Hongyuan Yan , Hui Wang
Dispersive liquid–liquid microextraction (DLLME) is a modern sample pretreatment technique that is regarded as consilient with the current trends of modern analytical chemistry. DLLME is simple, inexpensive, environmentally friendly, and could offer high enrichment factors from a wide gap between acceptor and donor phases. As a consequence, DLLME has attracted considerable attention from researchers and, based on the numerous publications concerning DLLME, has been generally accepted in separation science since the technique's invention in 2006. However, several innate weaknesses of DLLME, which restrict the technique's use in certain fields, have led to various attempts or suggestions to improve this technique. The present review focuses on the recent advances made in DLLME; the selected papers that are discussed in this work represent modifications that fall into three main categories (exploration of new extraction solvents, disperser solvents and combination with other techniques). The recent applications of DLLME in environmental, food and biological samples are also summarised, covering almost all of the publications related to the technology from the beginning. In addition, the feasibility of future trends of DLLME is discussed.
Source:Journal of Chromatography A, Volume 1295
Author(s): Hongyuan Yan , Hui Wang
Dispersive liquid–liquid microextraction (DLLME) is a modern sample pretreatment technique that is regarded as consilient with the current trends of modern analytical chemistry. DLLME is simple, inexpensive, environmentally friendly, and could offer high enrichment factors from a wide gap between acceptor and donor phases. As a consequence, DLLME has attracted considerable attention from researchers and, based on the numerous publications concerning DLLME, has been generally accepted in separation science since the technique's invention in 2006. However, several innate weaknesses of DLLME, which restrict the technique's use in certain fields, have led to various attempts or suggestions to improve this technique. The present review focuses on the recent advances made in DLLME; the selected papers that are discussed in this work represent modifications that fall into three main categories (exploration of new extraction solvents, disperser solvents and combination with other techniques). The recent applications of DLLME in environmental, food and biological samples are also summarised, covering almost all of the publications related to the technology from the beginning. In addition, the feasibility of future trends of DLLME is discussed.
Development and comparison of two dispersive liquid–liquid microextraction techniques coupled to high performance liquid chromatography for the rapid analysis of bisphenol A in edible oils
03 June 2013,
08:31:53
Publication date: 21 June
2013
Source:Journal of Chromatography A, Volume 1295
Author(s): Shuhui Liu , Qilong Xie , Jie Chen , Janzhi Sun , Hui He , Xiaoke Zhang
In this study, two novel sample extraction methods for the analysis of bisphenol A (BPA) in edible oils were developed by using liquid–liquid extraction followed by a dispersive liquid–liquid microextraction (LLE-DLLME) and reversed-phase dispersive liquid–liquid microextraction (RP-DLLME). RP-DLLME showed a superior characteristic over LLE-DLLME and other previously reported procedures because of its easy operation, short extraction time, high sensitivity, low organic solvent consumption and waste generation. The optimized extraction conditions of RP-DLLME for 1.0g of edible oil diluted in 4mL of n-hexane were: extractant, 100μL 0.2M sodium hydroxide solution (80% methanol, v/v); extraction time, 1min; centrifugation, 3min. The determination of BPA was carried out by high performance liquid chromatography coupled with a DAD detector. The method offered excellent linearity over a range of 0.010–0.5μgg−1 with a correlation coefficient of r >0.997. Intra-day and inter-day repeatability values expressed as relative standard deviation were 1.9% and 5.9%, respectively. The quantitation limit and detection limit were 6.3 and 2.5ngg−1. The target analyte was detected in 5 out of 16 edible oil samples. The recovery rates in real samples ranged from 89.5 to 99.7%.
Source:Journal of Chromatography A, Volume 1295
Author(s): Shuhui Liu , Qilong Xie , Jie Chen , Janzhi Sun , Hui He , Xiaoke Zhang
In this study, two novel sample extraction methods for the analysis of bisphenol A (BPA) in edible oils were developed by using liquid–liquid extraction followed by a dispersive liquid–liquid microextraction (LLE-DLLME) and reversed-phase dispersive liquid–liquid microextraction (RP-DLLME). RP-DLLME showed a superior characteristic over LLE-DLLME and other previously reported procedures because of its easy operation, short extraction time, high sensitivity, low organic solvent consumption and waste generation. The optimized extraction conditions of RP-DLLME for 1.0g of edible oil diluted in 4mL of n-hexane were: extractant, 100μL 0.2M sodium hydroxide solution (80% methanol, v/v); extraction time, 1min; centrifugation, 3min. The determination of BPA was carried out by high performance liquid chromatography coupled with a DAD detector. The method offered excellent linearity over a range of 0.010–0.5μgg−1 with a correlation coefficient of r >0.997. Intra-day and inter-day repeatability values expressed as relative standard deviation were 1.9% and 5.9%, respectively. The quantitation limit and detection limit were 6.3 and 2.5ngg−1. The target analyte was detected in 5 out of 16 edible oil samples. The recovery rates in real samples ranged from 89.5 to 99.7%.
Development of a simultaneous multiple solid-phase microextraction-single shot-gas chromatography/mass spectrometry method and application to aroma profile analysis of commercial coffee
03 June 2013,
08:31:53
Publication date: 21 June
2013
Source:Journal of Chromatography A, Volume 1295
Author(s): Changgook Lee , Younghoon Lee , Jae-Gon Lee , Alan J. Buglass
A simultaneous multiple solid-phase microextraction-single shot-gas chromatography mass spectrometry (smSPME-ss-GC/MS) method has been developed for headspace analysis. Up to four fibers (50/30μm DVB/CAR/PDMS) were used simultaneously for the extraction of aroma components from the headspace of a single sample chamber in order to increase sensitivity of aroma extraction. To avoid peak broadening and to maximize resolution, a simple cryofocusing technique was adopted during sequential thermal desorption of multiple SPME fibers prior to a ‘single shot’ chromatographic run. The method was developed and validated on a model flavor mixture, containing 81 known pure components. With the conditions of 10min of incubation and 30min of extraction at 50°C, single, dual, triple and quadruple SPME extractions were compared. The increase in total peak area with increase in the number of fibers showed good linearity (R 2 =0.9917) and the mean precision was 12.0% (RSD) for the total peak sum, with quadruple simultaneous SPME extraction. Using a real sample such as commercial coffee granules, aroma profile analysis was conducted using single, dual, triple and quadruple SPME fibers. The increase in total peak intensity again showed good linearity with increase in the number of SPME fibers used (R 2 =0.9992) and the precision of quadruple SPME extraction was 9.9% (RSD) for the total peak sum.
Source:Journal of Chromatography A, Volume 1295
Author(s): Changgook Lee , Younghoon Lee , Jae-Gon Lee , Alan J. Buglass
A simultaneous multiple solid-phase microextraction-single shot-gas chromatography mass spectrometry (smSPME-ss-GC/MS) method has been developed for headspace analysis. Up to four fibers (50/30μm DVB/CAR/PDMS) were used simultaneously for the extraction of aroma components from the headspace of a single sample chamber in order to increase sensitivity of aroma extraction. To avoid peak broadening and to maximize resolution, a simple cryofocusing technique was adopted during sequential thermal desorption of multiple SPME fibers prior to a ‘single shot’ chromatographic run. The method was developed and validated on a model flavor mixture, containing 81 known pure components. With the conditions of 10min of incubation and 30min of extraction at 50°C, single, dual, triple and quadruple SPME extractions were compared. The increase in total peak area with increase in the number of fibers showed good linearity (R 2 =0.9917) and the mean precision was 12.0% (RSD) for the total peak sum, with quadruple simultaneous SPME extraction. Using a real sample such as commercial coffee granules, aroma profile analysis was conducted using single, dual, triple and quadruple SPME fibers. The increase in total peak intensity again showed good linearity with increase in the number of SPME fibers used (R 2 =0.9992) and the precision of quadruple SPME extraction was 9.9% (RSD) for the total peak sum.
Preparation of a polar monolithic coating for stir bar sorptive extraction of emerging contaminants from wastewaters
03 June 2013,
08:31:53
Publication date: 21 June
2013
Source:Journal of Chromatography A, Volume 1295
Author(s): Núria Gilart , P.A.G. Cormack , Rosa Maria Marcé , Francesc Borrull , Núria Fontanals
A new polar monolith based on poly(poly(ethylene glycol) methacrylate-co-pentaerythritol triacrylate) (poly(PEGMA-co-PETRA)) was first synthesised, after the optimisation of the polymerisation conditions, and applied as a coating for the stir bar sorptive extraction (SBSE) of a group of pharmaceuticals and personal care products (PPCPs) from environmental water samples. Several parameters affecting extraction and liquid desorption in SBSE were investigated to achieve the optimal sorption efficiencies for the studied analytes. Under the optimised experimental conditions, a rapid, simple and sensitive SBSE performance was provided by the in-house monolithic stir bar. Moreover, the in-house coating was able to extract and desorb most of the studied analytes more effectively and quickly, due to its polar behaviour and suitable mechanical and physical properties, in comparison with the recently commercialised polar stir bars (EG Silicone Twister® and Acrylate Twister®). The analytical methodology, including SBSE followed by liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS), was validated and successfully applied for the determination of a group of PPCPs in wastewater samples.
Source:Journal of Chromatography A, Volume 1295
Author(s): Núria Gilart , P.A.G. Cormack , Rosa Maria Marcé , Francesc Borrull , Núria Fontanals
A new polar monolith based on poly(poly(ethylene glycol) methacrylate-co-pentaerythritol triacrylate) (poly(PEGMA-co-PETRA)) was first synthesised, after the optimisation of the polymerisation conditions, and applied as a coating for the stir bar sorptive extraction (SBSE) of a group of pharmaceuticals and personal care products (PPCPs) from environmental water samples. Several parameters affecting extraction and liquid desorption in SBSE were investigated to achieve the optimal sorption efficiencies for the studied analytes. Under the optimised experimental conditions, a rapid, simple and sensitive SBSE performance was provided by the in-house monolithic stir bar. Moreover, the in-house coating was able to extract and desorb most of the studied analytes more effectively and quickly, due to its polar behaviour and suitable mechanical and physical properties, in comparison with the recently commercialised polar stir bars (EG Silicone Twister® and Acrylate Twister®). The analytical methodology, including SBSE followed by liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS), was validated and successfully applied for the determination of a group of PPCPs in wastewater samples.
Identification of metabolites of honokiol in rat urine using 13C stable isotope labeling and liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry
03 June 2013,
08:31:53
Publication date: 21 June
2013
Source:Journal of Chromatography A, Volume 1295
Author(s): Juan Liu , Minghai Tang , Huijun Lai , Yinfeng Dong , Caifeng Xie , Haoyu Ye , Liang Ma , Neng Qiu , Yanfang Li , Lulu Cai , Lijuan Chen
A general approach based on stable isotope labeling and UPLC/Q-TOF-MS analysis of in vivo novel metabolites of honokiol has been developed in our study. In this method, urine samples were collected after intravenous administration of mixture of regular and [13C6]-labeled honokiol at 1:1 ratio to healthy rats. The metabolites could be easily recognized by the determination of a chromatographically co-eluted pair of isotopomers (MS doublet peaks) with similar peak intensities and mass difference corresponding to that between isotope-labeled and non-isotope-labeled honokiol. A total of 51 metabolites were detected, 37 of which were tentatively identified based on mass accuracy (<5ppm). Among them, 33 of honokiol metabolites were first reported with 5 metabolites belonging to phase I and other 32 metabolites belonging to phase II metabolites. Our results highlighted that the main phase I metabolic pathways of honokiol in rats were oxidation, and the phase II metabolic pathways were sulfation, glucuronidation, acetylation as well as amino acids conjugation. This was the first research focused on the biotransformation of honokiol in rats, and the identification of these metabolites might provide us essential information for further pharmacological and clinical studies of honokiol.
Source:Journal of Chromatography A, Volume 1295
Author(s): Juan Liu , Minghai Tang , Huijun Lai , Yinfeng Dong , Caifeng Xie , Haoyu Ye , Liang Ma , Neng Qiu , Yanfang Li , Lulu Cai , Lijuan Chen
A general approach based on stable isotope labeling and UPLC/Q-TOF-MS analysis of in vivo novel metabolites of honokiol has been developed in our study. In this method, urine samples were collected after intravenous administration of mixture of regular and [13C6]-labeled honokiol at 1:1 ratio to healthy rats. The metabolites could be easily recognized by the determination of a chromatographically co-eluted pair of isotopomers (MS doublet peaks) with similar peak intensities and mass difference corresponding to that between isotope-labeled and non-isotope-labeled honokiol. A total of 51 metabolites were detected, 37 of which were tentatively identified based on mass accuracy (<5ppm). Among them, 33 of honokiol metabolites were first reported with 5 metabolites belonging to phase I and other 32 metabolites belonging to phase II metabolites. Our results highlighted that the main phase I metabolic pathways of honokiol in rats were oxidation, and the phase II metabolic pathways were sulfation, glucuronidation, acetylation as well as amino acids conjugation. This was the first research focused on the biotransformation of honokiol in rats, and the identification of these metabolites might provide us essential information for further pharmacological and clinical studies of honokiol.
Multi-residue analytical method for the determination of endocrine disruptors and related compounds in river and waste water using dual column liquid chromatography switching system coupled to mass spectrometry
03 June 2013,
08:31:53
Publication date: 21 June
2013
Source:Journal of Chromatography A, Volume 1295
Author(s): Marina Gorga , Mira Petrovic , Damià Barceló
The present study describes a novel, fully automated method, based on column switching using EQuan™ columns for an integrated sample preconcentration and liquid chromatography coupled to tandem mass spectrometry (LC–LC–MS/MS). The method allows the unequivocal identification and quantification of the most relevant environmental endocrine disruptors compounds (EDCs) and compounds suspected to be EDCs, such as natural and synthetic estrogens and their conjugates, antimicrobials, parabens, bisphenol A, alkylphenolic compounds, benzotriazoles, and organophosphorus flame retardants, in surface river water and wastewater samples. Applying this technique, water samples were directly injected into the chromatographic system and the target compounds were concentrated into the loading column. Thereafter, the analytes were transferred into the analytical column for subsequent detection by MS–MS (QqQ). A comparative study employing three types of columns, with different chemical modifications, was performed in order to determine the optimal column that allowed maximum retention and subsequent elution of the analytes. Using this new optimized methodology a fast and easy online methodology for the analysis of EDCs in surface river water and wastewater with low limits of quantification (LOQ) was obtained. LOQs ranged from 0.008 to 1.54ng/L for surface river water and from 0.178/0.364 to 12.5/25.0ng/L (except for alkylphenol monoethoxylates) for effluent/influent waste water. Moreover, employing approximately 1h, a complete analysis was performed which was significant improvement in comparison to other methods reported previously. This method was used to track the presence and fate of target compounds in the Ebro River which is the most important river in Spain whose intensive agricultural and industrial activities concentrate mainly close to the main cities in the basin, deteriorating soil and water quality.
Source:Journal of Chromatography A, Volume 1295
Author(s): Marina Gorga , Mira Petrovic , Damià Barceló
The present study describes a novel, fully automated method, based on column switching using EQuan™ columns for an integrated sample preconcentration and liquid chromatography coupled to tandem mass spectrometry (LC–LC–MS/MS). The method allows the unequivocal identification and quantification of the most relevant environmental endocrine disruptors compounds (EDCs) and compounds suspected to be EDCs, such as natural and synthetic estrogens and their conjugates, antimicrobials, parabens, bisphenol A, alkylphenolic compounds, benzotriazoles, and organophosphorus flame retardants, in surface river water and wastewater samples. Applying this technique, water samples were directly injected into the chromatographic system and the target compounds were concentrated into the loading column. Thereafter, the analytes were transferred into the analytical column for subsequent detection by MS–MS (QqQ). A comparative study employing three types of columns, with different chemical modifications, was performed in order to determine the optimal column that allowed maximum retention and subsequent elution of the analytes. Using this new optimized methodology a fast and easy online methodology for the analysis of EDCs in surface river water and wastewater with low limits of quantification (LOQ) was obtained. LOQs ranged from 0.008 to 1.54ng/L for surface river water and from 0.178/0.364 to 12.5/25.0ng/L (except for alkylphenol monoethoxylates) for effluent/influent waste water. Moreover, employing approximately 1h, a complete analysis was performed which was significant improvement in comparison to other methods reported previously. This method was used to track the presence and fate of target compounds in the Ebro River which is the most important river in Spain whose intensive agricultural and industrial activities concentrate mainly close to the main cities in the basin, deteriorating soil and water quality.
Study of the peak variance in isocratic and gradient liquid chromatography using the transport model
03 June 2013,
08:31:53
Publication date: 21 June
2013
Source:Journal of Chromatography A, Volume 1295
Author(s): Weiqiang Hao , Bin Di , Qiang Chen , Junde Wang , Yongbin Yang , Xiaoli Sun
The expressions accounting for the peak variance in isocratic and gradient liquid chromatography is derived from the transport model. In mathematical treatments, the dwelling time is taken into account, and the type of solvent strength, gradient profile and the variation of plate height (H) with mobile phase composition (φ) is not specified. By applying a coordinate transformation, the transport model is solved by using the Laplace transform approach. A plate height equation that is suited for both isocratic and gradient elution is obtained. Based on this equation, the plate height equations for any combination of stepwise and linear gradients are derived. These equations will be algebraic when the solvent strength is linear and the H–φ plot is parabolic. The plate height equations for single stepwise, single linear and the ladder-like gradients are also given.
Source:Journal of Chromatography A, Volume 1295
Author(s): Weiqiang Hao , Bin Di , Qiang Chen , Junde Wang , Yongbin Yang , Xiaoli Sun
The expressions accounting for the peak variance in isocratic and gradient liquid chromatography is derived from the transport model. In mathematical treatments, the dwelling time is taken into account, and the type of solvent strength, gradient profile and the variation of plate height (H) with mobile phase composition (φ) is not specified. By applying a coordinate transformation, the transport model is solved by using the Laplace transform approach. A plate height equation that is suited for both isocratic and gradient elution is obtained. Based on this equation, the plate height equations for any combination of stepwise and linear gradients are derived. These equations will be algebraic when the solvent strength is linear and the H–φ plot is parabolic. The plate height equations for single stepwise, single linear and the ladder-like gradients are also given.
Determination of adsorbable organic fluorine from aqueous environmental samples by adsorption to polystyrene-divinylbenzene based activated carbon and combustion ion chromatography
03 June 2013,
08:31:53
Publication date: 21 June
2013
Source:Journal of Chromatography A, Volume 1295
Author(s): Andrea Wagner , Brigitte Raue , Heinz-Jürgen Brauch , Eckhard Worch , Frank T. Lange
A new method for the determination of trace levels of adsorbable organic fluorine (AOF) in water is presented. Even if the individual contributing target compounds are widely unknown, this surrogate parameter is suited to identify typical organofluorine contaminations, such as with polyfluorinated chemicals (PFCs), and represents a lower boundary of the organofluorine concentration in water bodies. It consists of the adsorption of organofluorine chemicals on a commercially available synthetic polystyrene-divinylbenzene based activated carbon (AC) followed by analysis of the loaded AC by hydropyrolysis combustion ion chromatography (CIC). Inorganic fluorine is displaced by excess nitrate during the extraction step and by washing the loaded activated carbon with an acidic sodium nitrate solution. Due to its high purity the synthetic AC had a very low and reproducible fluorine blank (0.3μg/g) compared to natural ACs (up to approximately 9μg/g). Using this AC, fluoride and the internal standard phosphate could be detected free of chromatographic interferences. With a sample volume of 100mL and 2× 100mg of AC packed into two extraction columns combined in series, a limit of quantification (LOQ), derived according to the German standard method DIN 32645, of 0.3μg/L was achieved. The recoveries of six model PFCs were determined from tap water and a municipal wastewater treatment plant (WWTP) effluent. Except for the extremely polar perfluoroacetic acid (recovery of approximately 10%) the model substances showed fairly good (50% for perfluorobutanoic acid (PFBA)) to very good fluorine recoveries (100±20% for perfluorooctanoic acid (PFOA), perfluorobutanesulfonate (PFBS), 6:2 fluorotelomersulfonate (6:2 FTS)), both from tap water and wastewater matrix. This new analytical protocol was exemplarily applied to several surface water and groundwater samples. The obtained AOF values were compared to the fluorine content of 19 target PFCs analyzed by high performance liquid chromatography–electrospray tandem mass spectrometry (HPLC–(−)ESI-MS/MS). In groundwater contaminated by PFC-containing aqueous film-forming foams (AFFFs) up to 50% of the AOF could be attributed to PFC target chemicals, while in diffuse contaminated samples only <5% of the AOF could be identified by PFC analysis.
Source:Journal of Chromatography A, Volume 1295
Author(s): Andrea Wagner , Brigitte Raue , Heinz-Jürgen Brauch , Eckhard Worch , Frank T. Lange
A new method for the determination of trace levels of adsorbable organic fluorine (AOF) in water is presented. Even if the individual contributing target compounds are widely unknown, this surrogate parameter is suited to identify typical organofluorine contaminations, such as with polyfluorinated chemicals (PFCs), and represents a lower boundary of the organofluorine concentration in water bodies. It consists of the adsorption of organofluorine chemicals on a commercially available synthetic polystyrene-divinylbenzene based activated carbon (AC) followed by analysis of the loaded AC by hydropyrolysis combustion ion chromatography (CIC). Inorganic fluorine is displaced by excess nitrate during the extraction step and by washing the loaded activated carbon with an acidic sodium nitrate solution. Due to its high purity the synthetic AC had a very low and reproducible fluorine blank (0.3μg/g) compared to natural ACs (up to approximately 9μg/g). Using this AC, fluoride and the internal standard phosphate could be detected free of chromatographic interferences. With a sample volume of 100mL and 2× 100mg of AC packed into two extraction columns combined in series, a limit of quantification (LOQ), derived according to the German standard method DIN 32645, of 0.3μg/L was achieved. The recoveries of six model PFCs were determined from tap water and a municipal wastewater treatment plant (WWTP) effluent. Except for the extremely polar perfluoroacetic acid (recovery of approximately 10%) the model substances showed fairly good (50% for perfluorobutanoic acid (PFBA)) to very good fluorine recoveries (100±20% for perfluorooctanoic acid (PFOA), perfluorobutanesulfonate (PFBS), 6:2 fluorotelomersulfonate (6:2 FTS)), both from tap water and wastewater matrix. This new analytical protocol was exemplarily applied to several surface water and groundwater samples. The obtained AOF values were compared to the fluorine content of 19 target PFCs analyzed by high performance liquid chromatography–electrospray tandem mass spectrometry (HPLC–(−)ESI-MS/MS). In groundwater contaminated by PFC-containing aqueous film-forming foams (AFFFs) up to 50% of the AOF could be attributed to PFC target chemicals, while in diffuse contaminated samples only <5% of the AOF could be identified by PFC analysis.
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