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Selected papers from the latest issue:
Hemimicelles/admicelles supported on magnetic graphene sheets for enhanced magnetic solid-phase extraction
04 September 2012,
09:13:42
Publication year:
2012
Source:Journal of Chromatography A, Volume 1257
Qian Liu, Jianbo Shi, Thanh Wang, Feng Guo, Lihong Liu, Guibin Jiang
In this work, superparamagnetic nanoparticle-decorated graphene (MG) sheets were synthesized and used as support for hemimicelles/admicelles for solid-phase extraction (SPE) of different compounds from environmental water samples for the first time. The MG sheets were facilely synthesized by a one-step, one-pot redox reaction between graphene oxide and Fe(II). Due to the large surface area and unique nanosheet morphology, MG served as an excellent nano-scaled support material for hemimicelles and admicelles, exhibiting higher loading capacity than conventional materials and pure Fe3O4 nanoparticles. The MG sheets could be negatively or positively charged depending on solution pH, allowing the extraction to be conducted in different modes. In cationic mode, cetyltrimethylammonium bromide (CTAB) was used as micelle-forming reagent, and perfluoroalkyl and polyfluoroalkyl substances (PFASs) and alkylphenols were used as model analytes. In anionic mode, sodium dodecyl sulfate (SDS) was used as micelle-forming reagent and alkyltrimethylammonium salts were selected as analytes. In both modes, the formation processes of hemimicelles/admicelles on MG sheets were studied and the extraction conditions were optimized. For PFASs, the analytical sensitivity was enhanced by 50–113-fold by the extraction, and the method detection limits (MDLs) ranged from 0.15 to 0.50ng/L. For alkyltrimethylammonium salts, the MDLs were in the range of 1.4–8.0ng/L. In both modes, good recoveries (56.3–93.9%) and reproducibility (run-to-run RSDs<9.3%) were obtained. The results from this work show a potential new role of graphene in analytical sample preparation.
Source:Journal of Chromatography A, Volume 1257
Qian Liu, Jianbo Shi, Thanh Wang, Feng Guo, Lihong Liu, Guibin Jiang
In this work, superparamagnetic nanoparticle-decorated graphene (MG) sheets were synthesized and used as support for hemimicelles/admicelles for solid-phase extraction (SPE) of different compounds from environmental water samples for the first time. The MG sheets were facilely synthesized by a one-step, one-pot redox reaction between graphene oxide and Fe(II). Due to the large surface area and unique nanosheet morphology, MG served as an excellent nano-scaled support material for hemimicelles and admicelles, exhibiting higher loading capacity than conventional materials and pure Fe3O4 nanoparticles. The MG sheets could be negatively or positively charged depending on solution pH, allowing the extraction to be conducted in different modes. In cationic mode, cetyltrimethylammonium bromide (CTAB) was used as micelle-forming reagent, and perfluoroalkyl and polyfluoroalkyl substances (PFASs) and alkylphenols were used as model analytes. In anionic mode, sodium dodecyl sulfate (SDS) was used as micelle-forming reagent and alkyltrimethylammonium salts were selected as analytes. In both modes, the formation processes of hemimicelles/admicelles on MG sheets were studied and the extraction conditions were optimized. For PFASs, the analytical sensitivity was enhanced by 50–113-fold by the extraction, and the method detection limits (MDLs) ranged from 0.15 to 0.50ng/L. For alkyltrimethylammonium salts, the MDLs were in the range of 1.4–8.0ng/L. In both modes, good recoveries (56.3–93.9%) and reproducibility (run-to-run RSDs<9.3%) were obtained. The results from this work show a potential new role of graphene in analytical sample preparation.
Highlights
► Magnetic graphene sheets were used as support for hemimicelles/admicelles for SPE. ► Magnetic graphene showed higher loading capacity than conventional materials. ► The SPE could be performed in cationic and anionic modes. ► The method showed good analytical performance for different types of analytes. ► The method was used for pretreatment of environmental water samples.A novel preconcentration strategy for extraction methods based on common cationic surfactants: An alternative to classical coacervative extraction
04 September 2012,
09:13:42
Publication year:
2012
Source:Journal of Chromatography A, Volume 1257
Bárbara Delgado, Verónica Pino, Juan H. Ayala, Ana M. Afonso, Venerando González
A novel and simple preconcentration step for aqueous micellar solutions of the common cationic surfactant cetyltrimethylammonium bromide (CTAB) has been developed. The procedure is based on the formation of another phase (a micro-droplet), not soluble in water, in which analytes (originally present in the aqueous solution) experience preconcentration. The method resembles to that of classical coacervation, but it does not require high ionic strengths neither acidic pH values. The optimum method implies mixing aqueous micellar solutions of CTAB with lithium bis[(trifluoromethane)sulfonyl]imide (Li-NTf2) in a 1:1 molar ratio with a 16.5% (v/v) of acetonitrile content, followed by vortex, heating at 65°C during 2min, and centrifugation. The obtained microdroplet containing analytes is then subjected to high-performance liquid chromatography (HPLC) with diode-array detection (DAD). The method has been applied to the determination of a group of organic contaminants including alkylphenols, polycyclic aromatic hydrocarbons and parabens, present in aqueous samples (including seawater) or solid samples (such as sediment samples, which are subjected to a previous microwave-assisted extraction). Average preconcentration factors of roughly 14 and 12 are obtained for aqueous and sediment samples, respectively; being the limits of quantification down to 0.5μgL−1 and 0.02mgkg−1, respectively.
Source:Journal of Chromatography A, Volume 1257
Bárbara Delgado, Verónica Pino, Juan H. Ayala, Ana M. Afonso, Venerando González
A novel and simple preconcentration step for aqueous micellar solutions of the common cationic surfactant cetyltrimethylammonium bromide (CTAB) has been developed. The procedure is based on the formation of another phase (a micro-droplet), not soluble in water, in which analytes (originally present in the aqueous solution) experience preconcentration. The method resembles to that of classical coacervation, but it does not require high ionic strengths neither acidic pH values. The optimum method implies mixing aqueous micellar solutions of CTAB with lithium bis[(trifluoromethane)sulfonyl]imide (Li-NTf2) in a 1:1 molar ratio with a 16.5% (v/v) of acetonitrile content, followed by vortex, heating at 65°C during 2min, and centrifugation. The obtained microdroplet containing analytes is then subjected to high-performance liquid chromatography (HPLC) with diode-array detection (DAD). The method has been applied to the determination of a group of organic contaminants including alkylphenols, polycyclic aromatic hydrocarbons and parabens, present in aqueous samples (including seawater) or solid samples (such as sediment samples, which are subjected to a previous microwave-assisted extraction). Average preconcentration factors of roughly 14 and 12 are obtained for aqueous and sediment samples, respectively; being the limits of quantification down to 0.5μgL−1 and 0.02mgkg−1, respectively.
Highlights
► A novel preconcentration method is developed for the common cationic surfactant CTAB. ► This efficient method is an alternative to the classical coacervative extraction. ► A group of EDPs, PAHs and parabens in aqueous and sediment samples has been studied. ► The method is fast: ∼8 to ∼15min, and almost organic solvent free: 300μLacn/sample.Zeolite imidazolate frameworks 8 as sorbent and its application to sonication-assisted emulsification microextraction combined with vortex-assisted porous membrane-protected micro-solid-phase extraction for fast analysis of acidic drugs in environmental water samples
04 September 2012,
09:13:42
Publication year:
2012
Source:Journal of Chromatography A, Volume 1257
Dandan Ge, Hian Kee Lee
A novel and fast procedure, sonication-assisted emulsification microextraction combined with vortex-assisted porous membrane protected micro-solid-phase extraction (SAEME-VA-μ-SPE), was developed for the gas chromatography–mass spectrometric determination of acidic drugs from environmental water samples. One advantage of the new procedure is that any solvent immiscible with water can be used as extractant solvent of SAEME and any solid sorbent can be used for μ-SPE in the SAEME-VA-μ-SPE process. In the present work, zeolite imidazolate framework 8 (ZIF-8) was employed as extraction sorbent for μ-SPE and 1-octanol as extractant solvent for SAEME. ZIF-8 has very good thermal, chemical and water stability, which make it a suitable material for the extraction of trace analytes from aqueous samples. Under the optimized extraction conditions, the developed method exhibited low limits of detection (0.01–0.04ng/ml), good linearity (with r 2 between 0.9965 and 0.9993) from 0.5 to 50ng/ml and satisfactory repeatability (between 4.1% and 7.6%). In essence SAEME-VA-μ-SPE is a combination of two different and efficient miniaturized techniques. It was demonstrated to be a fast, accurate, and convenient pretreatment procedure for trace analysis of environmental water samples.
Source:Journal of Chromatography A, Volume 1257
Dandan Ge, Hian Kee Lee
A novel and fast procedure, sonication-assisted emulsification microextraction combined with vortex-assisted porous membrane protected micro-solid-phase extraction (SAEME-VA-μ-SPE), was developed for the gas chromatography–mass spectrometric determination of acidic drugs from environmental water samples. One advantage of the new procedure is that any solvent immiscible with water can be used as extractant solvent of SAEME and any solid sorbent can be used for μ-SPE in the SAEME-VA-μ-SPE process. In the present work, zeolite imidazolate framework 8 (ZIF-8) was employed as extraction sorbent for μ-SPE and 1-octanol as extractant solvent for SAEME. ZIF-8 has very good thermal, chemical and water stability, which make it a suitable material for the extraction of trace analytes from aqueous samples. Under the optimized extraction conditions, the developed method exhibited low limits of detection (0.01–0.04ng/ml), good linearity (with r 2 between 0.9965 and 0.9993) from 0.5 to 50ng/ml and satisfactory repeatability (between 4.1% and 7.6%). In essence SAEME-VA-μ-SPE is a combination of two different and efficient miniaturized techniques. It was demonstrated to be a fast, accurate, and convenient pretreatment procedure for trace analysis of environmental water samples.
Highlights
► A novel and fast preconcentration approach, SAEME-VA-μ-SPE was developed. ► Any extractant solvent immiscible with water, and any sorbent, can be used for SAEME-VA-μ-SPE. ► Simple, fast and efficient microextraction method with good linearity, low LODs and %RSDs.An approach based on ultra-high pressure liquid chromatography–tandem mass spectrometry to quantify O6-methyl and O6-carboxymethylguanine DNA adducts in intestinal cell lines
04 September 2012,
09:13:42
Publication year:
2012
Source:Journal of Chromatography A, Volume 1257
J. Vanden Bussche, S.A. Moore, F. Pasmans, G.G.C. Kuhnle, L. Vanhaecke
O6-methylguanine (O6-MeG) and O6-carboxymethylguanine (O6-CMG) are characteristic promutagenic and toxic DNA adducts formed by nitrosated glycine derivates and N-nitrosopeptides. Since endogenous nitrosation has been hypothesised as a plausible origin for the association between red and processed meat intake and colorectal cancer, a highly sensitive, fast and specific quantitative assay is needed to correlate the dose of individual DNA adducts with the effects of food consumption and individual digestive and metabolic processes. An ultra-high pressure liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) assay for quantitation of O6-MeG and O6-CMG, using the deuterated analogues as internal standards (ISTD), was developed. Samples of calf thymus DNA containing O6-MeG and O6-CMG were purified by acid hydrolysis and solid phase extraction prior to quantification by UHPLC–MS/MS in the selected reaction monitoring mode. The method was successfully validated in terms of repeatability (RSD<10%), reproducibility (RSD<15%) and linearity (99.9%) by incubating 0.1mg calf thymus DNA with the known N-nitroso compound potassium diazoacetate (KDA). The limit of quantitation was 30fmolmg−1 DNA for O6-MeG or 1 adduct per 108 nucleotides and 50fmolmg−1 DNA for O6-CMG or 1.7 adducts per 108 nucleotides. Subsequently, the method was applied to human colon carcinoma cell lines, Caco-2 and HT-29, treated with KDA to illustrate its capability to quantify O6-MeG and O6-CMG DNA adducts using biological relevant models in vitro. This method will support further research to unravel the mechanistic basis of endogenous nitrosation processes upon consumption of red and processed meat products.
Source:Journal of Chromatography A, Volume 1257
J. Vanden Bussche, S.A. Moore, F. Pasmans, G.G.C. Kuhnle, L. Vanhaecke
O6-methylguanine (O6-MeG) and O6-carboxymethylguanine (O6-CMG) are characteristic promutagenic and toxic DNA adducts formed by nitrosated glycine derivates and N-nitrosopeptides. Since endogenous nitrosation has been hypothesised as a plausible origin for the association between red and processed meat intake and colorectal cancer, a highly sensitive, fast and specific quantitative assay is needed to correlate the dose of individual DNA adducts with the effects of food consumption and individual digestive and metabolic processes. An ultra-high pressure liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) assay for quantitation of O6-MeG and O6-CMG, using the deuterated analogues as internal standards (ISTD), was developed. Samples of calf thymus DNA containing O6-MeG and O6-CMG were purified by acid hydrolysis and solid phase extraction prior to quantification by UHPLC–MS/MS in the selected reaction monitoring mode. The method was successfully validated in terms of repeatability (RSD<10%), reproducibility (RSD<15%) and linearity (99.9%) by incubating 0.1mg calf thymus DNA with the known N-nitroso compound potassium diazoacetate (KDA). The limit of quantitation was 30fmolmg−1 DNA for O6-MeG or 1 adduct per 108 nucleotides and 50fmolmg−1 DNA for O6-CMG or 1.7 adducts per 108 nucleotides. Subsequently, the method was applied to human colon carcinoma cell lines, Caco-2 and HT-29, treated with KDA to illustrate its capability to quantify O6-MeG and O6-CMG DNA adducts using biological relevant models in vitro. This method will support further research to unravel the mechanistic basis of endogenous nitrosation processes upon consumption of red and processed meat products.
Highlights
► Optimisation of the extraction of O6-carboxymethylguanine and O6-methylguanine. ► Development and proper validation of an UHPLC–MS/MS detection method. ► Working with pre-extracted DNA instead of cultured cell lines is more efficient. ► Applicability of the detection method for in vitro and in vivo experiments.Quantification of selected furocoumarins by high-performance liquid chromatography and UV-detection: Capabilities and limits
04 September 2012,
09:13:42
Publication year:
2012
Source:Journal of Chromatography A, Volume 1257
Angus P. Macmaster, Neil Owen, Sylvain Brussaux, Hugues Brevard, Richard Hiserodt, Hans Leijs, Nikola Bast, Berthold Weber, Gerd Loesing, Alan Sherlock, Christine Schippa, Matthias Vey, Eric Frérot, Emeline Tissot, Alain Chaintreau
The performance of HPLC–UV as a means of quantifying selected furocoumarins in essential oils has been evaluated, based on a ring test validation approach. Accuracy profiles were generated, to determine bias and statistical confidence associated with determination at different concentrations, along with lower limits of quantification (LOQ). From these findings, it can be concluded that the method described may only be used in simple cases (essential oils), to measure individual furocoumarin compounds at concentrations greater than 10mg/l; the non compound-specific nature of detection by absorption in the UV range is unable to overcome the effect of interferences arising from chromatographic coelutions, such as those encountered in the analysis of complex commercial fragrance mixtures. The use of an algorithmically calculated ‘spectral similarity’ function, with reference to authentic standards, may be used to improve reliability in assignment and quantification.
Source:Journal of Chromatography A, Volume 1257
Angus P. Macmaster, Neil Owen, Sylvain Brussaux, Hugues Brevard, Richard Hiserodt, Hans Leijs, Nikola Bast, Berthold Weber, Gerd Loesing, Alan Sherlock, Christine Schippa, Matthias Vey, Eric Frérot, Emeline Tissot, Alain Chaintreau
The performance of HPLC–UV as a means of quantifying selected furocoumarins in essential oils has been evaluated, based on a ring test validation approach. Accuracy profiles were generated, to determine bias and statistical confidence associated with determination at different concentrations, along with lower limits of quantification (LOQ). From these findings, it can be concluded that the method described may only be used in simple cases (essential oils), to measure individual furocoumarin compounds at concentrations greater than 10mg/l; the non compound-specific nature of detection by absorption in the UV range is unable to overcome the effect of interferences arising from chromatographic coelutions, such as those encountered in the analysis of complex commercial fragrance mixtures. The use of an algorithmically calculated ‘spectral similarity’ function, with reference to authentic standards, may be used to improve reliability in assignment and quantification.
Highlights
► HPLC with UV detection is the usual method to quantify furocoumarins, with contradictory reported quantification limits (0.019–61mg/l). ► This collaborative test shows that this method is only applicable to simple cases, above a limit of 10mg/l. ► To be valid, each quantitative result should be supported by the positive identification of the analyte comparing its UV spectrum to that of a authentic substance.Rapid quantification of protein–polyethylene glycol conjugates by multivariate evaluation of chromatographic data
04 September 2012,
09:13:42
Publication year:
2012
Source:Journal of Chromatography A, Volume 1257
Sigrid K. Hansen, Benjamin Maiser, Jürgen Hubbuch
Size exclusion chromatography (SEC) is often applied for characterization of protein–polyethylene glycol (PEG) conjugates regarding the number of attached PEG chains (PEGamers). SEC analysis is advantageous as it is precise, robust, and straightforward to establish. However, most SEC based assays have a maximal throughput of a few samples per hour. We present a strategy to increase analytical throughput based on combining a short column with a fast flow rate, and finally multivariate calibration in order to compensate for the resolution lost in the trade off for speed. Different multivariate approaches were compared and multilinear regression was shown to result in the most precise calibrations. Further, a dynamic calibration approach was developed in order to account for changes in column performance over time. In this way, it was possible to establish a highly precise assay for protein PEGamer quantification with a throughput of 30 samples per hour.
Source:Journal of Chromatography A, Volume 1257
Sigrid K. Hansen, Benjamin Maiser, Jürgen Hubbuch
Size exclusion chromatography (SEC) is often applied for characterization of protein–polyethylene glycol (PEG) conjugates regarding the number of attached PEG chains (PEGamers). SEC analysis is advantageous as it is precise, robust, and straightforward to establish. However, most SEC based assays have a maximal throughput of a few samples per hour. We present a strategy to increase analytical throughput based on combining a short column with a fast flow rate, and finally multivariate calibration in order to compensate for the resolution lost in the trade off for speed. Different multivariate approaches were compared and multilinear regression was shown to result in the most precise calibrations. Further, a dynamic calibration approach was developed in order to account for changes in column performance over time. In this way, it was possible to establish a highly precise assay for protein PEGamer quantification with a throughput of 30 samples per hour.
Highlights
► High throughput analytics approach for protein PEGamers successfully demonstrated. ► Low analysis time for SEC based quantification of protein PEGamers of 2min. ► Multivariate calibration compensates resolution sacrificed to gain analytical speed.Dynamic behavior of binary component ion-exchange displacement chromatography of proteins visualized by confocal laser scanning microscopy
04 September 2012,
09:13:42
Publication year:
2012
Source:Journal of Chromatography A, Volume 1257
Qing-Hong Shi, Zhi-Cong Shi, Yan Sun
Confocal laser scanning microscopy (CLSM) was introduced to visualize particle-scale binary component protein displacement behavior in Q Sepharose HP column. To this end, displacement chromatography of two intrinsic fluorescent proteins, enhanced green fluorescent protein (eGFP) and red fluorescent protein (RFP), were developed using sodium saccharin (NaSac) as a displacer. The results indicated that RFP as well as eGFP could be effectively displaced in the single-component experiments by 50mmol/L NaSac at 120 and 140mmol/L NaCl whereas a fully developed displacement train with eGFP and RFP was only observed at 120mmol/L NaCl in binary component displacement. At 140mmol/L NaCl, there was a serious overlapping of the zones of the two proteins, indicating the importance of induced-salt effect on the formation of an isotachic displacement train. CLSM provided particle-scale evidence that induced-salt effect occurred likewise in the interior of an adsorbent and was synchronous to the introduction of the displacer. CLSM results at 140mmol/L NaCl also demonstrated that both the proteins had the same fading rate at 50mmol/L NaSac in the initial stage, suggesting the same displacement ability of NaSac to both the proteins. In the final stage, the fading rate of RFP in the adsorbent became slow, particularly at lower displacer concentrations. In the binary component displacement, the two proteins exhibited distinct fading rates as compared to the single component displacement and the remarkable lagging of the fading rate was observed in protein displacements. It suggested that the co-adsorbed proteins had significant influence on the formation of an isotachic train and the displacement chromatography of the proteins. Therefore, this research provided particle-scale insight into the dynamic behavior and complexity in the displacement of proteins.
Source:Journal of Chromatography A, Volume 1257
Qing-Hong Shi, Zhi-Cong Shi, Yan Sun
Confocal laser scanning microscopy (CLSM) was introduced to visualize particle-scale binary component protein displacement behavior in Q Sepharose HP column. To this end, displacement chromatography of two intrinsic fluorescent proteins, enhanced green fluorescent protein (eGFP) and red fluorescent protein (RFP), were developed using sodium saccharin (NaSac) as a displacer. The results indicated that RFP as well as eGFP could be effectively displaced in the single-component experiments by 50mmol/L NaSac at 120 and 140mmol/L NaCl whereas a fully developed displacement train with eGFP and RFP was only observed at 120mmol/L NaCl in binary component displacement. At 140mmol/L NaCl, there was a serious overlapping of the zones of the two proteins, indicating the importance of induced-salt effect on the formation of an isotachic displacement train. CLSM provided particle-scale evidence that induced-salt effect occurred likewise in the interior of an adsorbent and was synchronous to the introduction of the displacer. CLSM results at 140mmol/L NaCl also demonstrated that both the proteins had the same fading rate at 50mmol/L NaSac in the initial stage, suggesting the same displacement ability of NaSac to both the proteins. In the final stage, the fading rate of RFP in the adsorbent became slow, particularly at lower displacer concentrations. In the binary component displacement, the two proteins exhibited distinct fading rates as compared to the single component displacement and the remarkable lagging of the fading rate was observed in protein displacements. It suggested that the co-adsorbed proteins had significant influence on the formation of an isotachic train and the displacement chromatography of the proteins. Therefore, this research provided particle-scale insight into the dynamic behavior and complexity in the displacement of proteins.
Highlights
► CLSM was introduced to visualize particle-scale displacement of binary proteins. ► Two native fluorescent proteins were used to establish a novel displacement system. ► Induced-salt effect was synchronous to the application of displacer in particles. ► The research exhibited good relevance between chromatography and CLSM observations.Effect of silica gel modification with cyclofructans on properties of hydrophilic interaction liquid chromatography stationary phases
04 September 2012,
09:13:42
Publication year:
2012
Source:Journal of Chromatography A, Volume 1257
Petr Kozlík, Veronika Šímová, Květa Kalíková, Zuzana Bosáková, Daniel W. Armstrong, Eva Tesařová
Hydrophilic interaction liquid chromatography (HILIC) offers very good possibilities for separation of polar compounds as an alternative to reversed phase HPLC where polar compounds are not sufficiently retained. HILIC is becoming more popular for the analysis of biologically interesting (active) analytes. Various stationary phases are commercially available however, development of new materials (sorbents) suitable for HILIC systems still continues. Silica gel columns can be used directly but their modification can improve separation ability of the stationary phases. Cyclofructan-based stationary phases are demonstrated as possible HILIC columns in this work. The effect of silica gel modification by cyclofructan and a derivatized cyclofructan was studied in detail. HILIC separation systems with silica gel, cyclofructan and isopropyl cyclofructan modified silica stationary phases were compared. The detailed study of chromatographic behavior of peptides revealed that multimodal retention mechanism is present in systems with these stationary phases. Mobile phase composition changes the types of interactions and their strengths. It appears that ability to donate protons and dispersion forces are the main interactions that affect retention in HILIC with cyclofructan-based columns while they are less important in separation systems with bare silica stationary phase. Suitability of cyclofructan-based stationary phases in HILIC for separation of pentapeptides and nonapeptides was demonstrated.
Source:Journal of Chromatography A, Volume 1257
Petr Kozlík, Veronika Šímová, Květa Kalíková, Zuzana Bosáková, Daniel W. Armstrong, Eva Tesařová
Hydrophilic interaction liquid chromatography (HILIC) offers very good possibilities for separation of polar compounds as an alternative to reversed phase HPLC where polar compounds are not sufficiently retained. HILIC is becoming more popular for the analysis of biologically interesting (active) analytes. Various stationary phases are commercially available however, development of new materials (sorbents) suitable for HILIC systems still continues. Silica gel columns can be used directly but their modification can improve separation ability of the stationary phases. Cyclofructan-based stationary phases are demonstrated as possible HILIC columns in this work. The effect of silica gel modification by cyclofructan and a derivatized cyclofructan was studied in detail. HILIC separation systems with silica gel, cyclofructan and isopropyl cyclofructan modified silica stationary phases were compared. The detailed study of chromatographic behavior of peptides revealed that multimodal retention mechanism is present in systems with these stationary phases. Mobile phase composition changes the types of interactions and their strengths. It appears that ability to donate protons and dispersion forces are the main interactions that affect retention in HILIC with cyclofructan-based columns while they are less important in separation systems with bare silica stationary phase. Suitability of cyclofructan-based stationary phases in HILIC for separation of pentapeptides and nonapeptides was demonstrated.
Highlights
► Two CF-based and bare silica SPs were compared in terms of separation performance. ► Modification of silica gel with CFs resulted in improved separation performance. ► Interactions participating in the retention and separation mechanism were identified by LFER. ► The main interactions on CF-based SPs are hydrogen bond acidity and dipolarity/polarizibility.Filter-based infrared detectors for high temperature size exclusion chromatography analysis of polyolefins: Calibration with a small number of standards and error analysis
04 September 2012,
09:13:42
Publication year:
2012
Source:Journal of Chromatography A, Volume 1257
A. Ortín, E. López, B. Monrabal, J.R. Torres-Lapasió, M.C. García-Álvarez-Coque
Infrared detection has been shown to be very appropriate for high temperature analysis of polyolefins. After some early reports in which dispersive or single-band filter-based detectors were applied, Fourier transform detectors have been described for this application, in order to improve the method sensitivity. Modern simple filter-based detectors prove, however, comparable sensitivity while providing a number of practical advantages when coupled to chromatographic systems: reduced cell volume, simplified hardware, continuous generation of absorbance chromatograms, as well as simpler data collection and processing. A practical method for calibration, using multiple-band signals obtained with filter-based detectors and a small number of reference materials, is here discussed. Calibration data are used to compare the performance of detectors based on different opto-electronic technologies and filter designs. A procedure for estimation of errors in the slice-by-slice measured methyl frequency, based on signal-to-noise ratio considerations, is described. The good accuracy provided by the filter-based IR detectors was noticeable, considering that it was obtained using a small set of reference materials. A minimal concentration of 0.009mg/mL was estimated to be required at the detector cell, in order to keep the errors below one unit of methyl per one thousand total carbons. This low minimal concentration requirement allows using standard SEC conditions, without compromising the molar mass distribution accuracy and resolution.
Source:Journal of Chromatography A, Volume 1257
A. Ortín, E. López, B. Monrabal, J.R. Torres-Lapasió, M.C. García-Álvarez-Coque
Infrared detection has been shown to be very appropriate for high temperature analysis of polyolefins. After some early reports in which dispersive or single-band filter-based detectors were applied, Fourier transform detectors have been described for this application, in order to improve the method sensitivity. Modern simple filter-based detectors prove, however, comparable sensitivity while providing a number of practical advantages when coupled to chromatographic systems: reduced cell volume, simplified hardware, continuous generation of absorbance chromatograms, as well as simpler data collection and processing. A practical method for calibration, using multiple-band signals obtained with filter-based detectors and a small number of reference materials, is here discussed. Calibration data are used to compare the performance of detectors based on different opto-electronic technologies and filter designs. A procedure for estimation of errors in the slice-by-slice measured methyl frequency, based on signal-to-noise ratio considerations, is described. The good accuracy provided by the filter-based IR detectors was noticeable, considering that it was obtained using a small set of reference materials. A minimal concentration of 0.009mg/mL was estimated to be required at the detector cell, in order to keep the errors below one unit of methyl per one thousand total carbons. This low minimal concentration requirement allows using standard SEC conditions, without compromising the molar mass distribution accuracy and resolution.
Highlights
► Use of filter-based IR detectors in high temperature SEC. ► Determination of methyl frequency along the molar mass distribution of polyolefins. ► Calibration with a small number of standards. ► Estimation of the confidence in the determination of methyl frequency.Quantitative determination of several toxicological important mycotoxins in pig plasma using multi-mycotoxin and analyte-specific high performance liquid chromatography–tandem mass spectrometric methods
04 September 2012,
09:13:42
Publication year:
2012
Source:Journal of Chromatography A, Volume 1257
Mathias Devreese, Siegrid De Baere, Patrick De Backer, Siska Croubels
A sensitive and reliable multi-mycotoxin method was developed for the identification and quantification of several toxicological important mycotoxins such as deoxynivalenol (DON), deepoxy-deoxynivalenol (DOM-1), T-2 toxin (T-2), HT-2 toxin (HT-2), zearalenone (ZON), zearalanone (ZAN), α-zearalenol (α-ZOL), β-zearalenol (β-ZOL), α-zearalanol (α-ZAL), β-zearalanol (β-ZAL), ochratoxin A (OTA), fumonisin B1 (FB1) and aflatoxin B1 (AFB1) in pig plasma using liquid chromatography combined with heated electrospray ionization triple quadrupole tandem mass spectrometry (LC–h-ESI-MS/MS). Sample clean-up consisted of a deproteinization step using acetonitrile, followed by evaporation of the supernatant and resuspension of the dry residue in water/methanol (85/15, v/v). Each plasma sample was analyzed twice, i.e. once in the ESI+ and ESI− mode, respectively. This method can be used for the assessment of animal exposure to mycotoxins and in the diagnosis of mycotoxicoses. For the performance of toxicokinetic studies with individual mycotoxins, highly sensitive analyte-specific LC–MS/MS methods were developed. The multi-mycotoxin and analyte-specific methods were in-house validated: matrix-matched calibration graphs were prepared for all compounds and correlation and goodness-of-fit coefficients ranged between 0.9974–0.9999 and 2.4–15.5%, respectively. The within- and between-run precision and accuracy were evaluated and the results fell within the ranges specified. The limits of quantification for the multi-mycotoxin and analyte-specific methods ranged from 2 to 10ng/mL and 0.5 to 5ng/mL, respectively, whereas limits of detection fell between 0.01–0.52ng/mL and <0.01–0.15ng/mL, respectively.
Source:Journal of Chromatography A, Volume 1257
Mathias Devreese, Siegrid De Baere, Patrick De Backer, Siska Croubels
A sensitive and reliable multi-mycotoxin method was developed for the identification and quantification of several toxicological important mycotoxins such as deoxynivalenol (DON), deepoxy-deoxynivalenol (DOM-1), T-2 toxin (T-2), HT-2 toxin (HT-2), zearalenone (ZON), zearalanone (ZAN), α-zearalenol (α-ZOL), β-zearalenol (β-ZOL), α-zearalanol (α-ZAL), β-zearalanol (β-ZAL), ochratoxin A (OTA), fumonisin B1 (FB1) and aflatoxin B1 (AFB1) in pig plasma using liquid chromatography combined with heated electrospray ionization triple quadrupole tandem mass spectrometry (LC–h-ESI-MS/MS). Sample clean-up consisted of a deproteinization step using acetonitrile, followed by evaporation of the supernatant and resuspension of the dry residue in water/methanol (85/15, v/v). Each plasma sample was analyzed twice, i.e. once in the ESI+ and ESI− mode, respectively. This method can be used for the assessment of animal exposure to mycotoxins and in the diagnosis of mycotoxicoses. For the performance of toxicokinetic studies with individual mycotoxins, highly sensitive analyte-specific LC–MS/MS methods were developed. The multi-mycotoxin and analyte-specific methods were in-house validated: matrix-matched calibration graphs were prepared for all compounds and correlation and goodness-of-fit coefficients ranged between 0.9974–0.9999 and 2.4–15.5%, respectively. The within- and between-run precision and accuracy were evaluated and the results fell within the ranges specified. The limits of quantification for the multi-mycotoxin and analyte-specific methods ranged from 2 to 10ng/mL and 0.5 to 5ng/mL, respectively, whereas limits of detection fell between 0.01–0.52ng/mL and <0.01–0.15ng/mL, respectively.
Highlights
► We developed LC–MS/MS methods for the analysis of important mycotoxins in plasma. ► Multi-mycotoxin and analyte-specific methods were developed. ► Methods allowing the determination of the analytes at the low ng/mL range. ► A rapid and simple sample preparation. ► The validated methods were applied to real plasma samples.High performance liquid chromatography–tandem mass spectrometry method for quantifying phenylurea herbicides and their main metabolites in amended and unamended soils
04 September 2012,
09:13:42
Publication year:
2012
Source:Journal of Chromatography A, Volume 1257
José Fenoll, Pilar Hellín, Carmen María Martínez, Pilar Flores, Simón Navarro
A sensitive multiresidue method for the simultaneous determination of sixteen phenylurea herbicides and their main metabolites in amended soils has been developed. Liquid chromatography tandem–mass spectrometry (LC–MS2) in electrospray ionization positive mode was used for the separation, identification and quantification of these compounds. The procedure involves initial single phase extraction of soil sample with acetonitrile by sonication, followed by liquid–liquid partitioning formed by addition of NaCl. The average recovery by the LC–MS2 method obtained for these compounds varied from 76.2 to 107.9% with a relative standard deviation ranging from 2.1 to 5.8%. The method presents good linearity (R 2 >0.99) over the range assayed 10–1000μgL−1 (except N-phenylurea 50–1000μgL−1). The detection limits for the compounds studied varied from 0.1 to 9.0ngg−1.
Source:Journal of Chromatography A, Volume 1257
José Fenoll, Pilar Hellín, Carmen María Martínez, Pilar Flores, Simón Navarro
A sensitive multiresidue method for the simultaneous determination of sixteen phenylurea herbicides and their main metabolites in amended soils has been developed. Liquid chromatography tandem–mass spectrometry (LC–MS2) in electrospray ionization positive mode was used for the separation, identification and quantification of these compounds. The procedure involves initial single phase extraction of soil sample with acetonitrile by sonication, followed by liquid–liquid partitioning formed by addition of NaCl. The average recovery by the LC–MS2 method obtained for these compounds varied from 76.2 to 107.9% with a relative standard deviation ranging from 2.1 to 5.8%. The method presents good linearity (R 2 >0.99) over the range assayed 10–1000μgL−1 (except N-phenylurea 50–1000μgL−1). The detection limits for the compounds studied varied from 0.1 to 9.0ngg−1.
Highlights
► Sonication-LC–MS2 allowed simultaneous determination of PUHs in amended soils. ► The method was very sensitive, selective and matrix effect was not observed. ► Repeatability and recovery were found to be within the range of acceptance.Fabrication and evaluation of low-cost agarose–zinc nanoporous composite matrix: Influence of adsorbent density and size distribution on the performance of expanded beds
04 September 2012,
09:13:42
Publication year:
2012
Source:Journal of Chromatography A, Volume 1257
Fateme Asghari, Mohsen Jahanshahi
Expanded bed adsorption (EBA), a promising and practical separation technique for adsorption of nanobioproduct/bioproduct, has been widely studied in the past two decades. The development of adsorbent with the special design for expanded bed process is a challenging course. To reduce the costs of adsorbent preparation, fine zinc powder was used as the inexpensive densifier. A series of matrices named Ag–Zn were prepared by water-in-oil emulsification method. The structure and morphology of the prepared matrix were studied by the optical microscope (OM) and scanning electron microscopy (SEM). The physical properties as a function of zinc powder ratio to agarose slurry were measured. The prepared matrices had regular spherical shape, and followed logarithmic normal size distribution with the range of 75–330μm, mean diameter of 140.54–191.11μm, wet density of 1.33–2.01g/ml, water content of 0.45–0.75, porosity of 0.86–0.97 and pore size of about 40–90nm. The bed expansion factor at the range of 2–3 was examined. The obtained results indicated that the expansion factor was decreased with increasing of matrix density. In addition, it was found that matrices with large particle size were suitable for high operation flow rate. The hydrodynamic properties were determined in expanded bed by the residence time distribution method (RTD). The effects of flow velocity, expansion factor and density of matrix on the hydrodynamic properties were also investigated. Moreover, the influence of particle size distribution on the performance of expanded bed has been studied. Therefore, three different particle size fractions (65–140, 215–280 and 65–280μm) were assessed. The results indicated that dispersion in liquid–solid expanded beds increased with increasing flow rate and expansion factor; and matrix with a wide particle size distribution leaded to a reduced axial dispersion compared to matrices with a narrow size distribution. The axial dispersion coefficient also enhanced with the increasing of matrix density. It was found that flow rate was the most essential factor to effect on the hydrodynamic characteristics in the bed. For all the prepared matrices, the values of axial mixing coefficients (D axl) were smaller than 1.0×10−5 m2/s when flow velocities in expanded bed were less than 700cm/h. All the results indicate that the prepared matrix show good expansion and stability in expanded bed; and it is suitable for expanded bed processes as an economical adsorbent.
Source:Journal of Chromatography A, Volume 1257
Fateme Asghari, Mohsen Jahanshahi
Expanded bed adsorption (EBA), a promising and practical separation technique for adsorption of nanobioproduct/bioproduct, has been widely studied in the past two decades. The development of adsorbent with the special design for expanded bed process is a challenging course. To reduce the costs of adsorbent preparation, fine zinc powder was used as the inexpensive densifier. A series of matrices named Ag–Zn were prepared by water-in-oil emulsification method. The structure and morphology of the prepared matrix were studied by the optical microscope (OM) and scanning electron microscopy (SEM). The physical properties as a function of zinc powder ratio to agarose slurry were measured. The prepared matrices had regular spherical shape, and followed logarithmic normal size distribution with the range of 75–330μm, mean diameter of 140.54–191.11μm, wet density of 1.33–2.01g/ml, water content of 0.45–0.75, porosity of 0.86–0.97 and pore size of about 40–90nm. The bed expansion factor at the range of 2–3 was examined. The obtained results indicated that the expansion factor was decreased with increasing of matrix density. In addition, it was found that matrices with large particle size were suitable for high operation flow rate. The hydrodynamic properties were determined in expanded bed by the residence time distribution method (RTD). The effects of flow velocity, expansion factor and density of matrix on the hydrodynamic properties were also investigated. Moreover, the influence of particle size distribution on the performance of expanded bed has been studied. Therefore, three different particle size fractions (65–140, 215–280 and 65–280μm) were assessed. The results indicated that dispersion in liquid–solid expanded beds increased with increasing flow rate and expansion factor; and matrix with a wide particle size distribution leaded to a reduced axial dispersion compared to matrices with a narrow size distribution. The axial dispersion coefficient also enhanced with the increasing of matrix density. It was found that flow rate was the most essential factor to effect on the hydrodynamic characteristics in the bed. For all the prepared matrices, the values of axial mixing coefficients (D axl) were smaller than 1.0×10−5 m2/s when flow velocities in expanded bed were less than 700cm/h. All the results indicate that the prepared matrix show good expansion and stability in expanded bed; and it is suitable for expanded bed processes as an economical adsorbent.
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