Just Published: Journal of Chromatography A

A new issue of this journal has just been published. To see abstracts of the papers it contains (with links through to the full papers) click here:

Journal of Chromatography A

http://rss.sciencedirect.com/publication/science/5248

Selected papers from the latest issue:

Ultrasound-assisted surfactant-enhanced emulsification microextraction for the determination of carbamates in wines by ultra-high performance liquid chromatography–tandem mass spectrometry

17 October 2013, 09:29:13

Publication date: 8 November 2013
Source:Journal of Chromatography A, Volume 1315
Author(s): David Moreno-González , José F. Huertas-Pérez , Ana M. García-Campaña , Juan M. Bosque-Sendra , Laura Gámiz-Gracia
A new sensitive multiresidue method based on ultra-high performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) has been developed for the detection, confirmation and quantification of twenty five carbamates in wine samples. The separation was achieved in 5.5min, using a Zorbax Eclipse plus RRHD C18 column (50mm×2.1mm, 1.8μm), with a mobile phase of water and methanol, both of them with 0.01% formic acid. The analytes were detected in positive mode with multiple reaction monitoring mode. Ultrasound-assisted surfactant-enhanced emulsification microextraction (UASEME), using a low-density extraction solvent has been optimized for the satisfactory extraction of carbamates and clean-up of extracts. The matrix effect was studied, showing that the proposed procedure provides very clean extracts. Under optimum conditions, recoveries for fortified wine samples ranged from 74 to 102%, with relative standard deviations lower than 6%. Limits of quantification ranged from 0.15 to 0.92μgl⁻¹, showing the high sensitivity of this fast and simple method and its compliance with current requirements.

Evaluation of passive samplers with neutral or ion-exchange polymer coatings to determine freely dissolved concentrations of the basic surfactant lauryl diethanolamine: Measurements of acid dissociation constant and organic carbon–water sorption coefficient

17 October 2013, 09:29:13

Publication date: 8 November 2013
Source:Journal of Chromatography A, Volume 1315
Author(s): Fang Wang , Yi Chen , Joop L.M. Hermens , Steven T.J. Droge
A passive sampler tool (solid-phase microextraction, SPME) was optimized to measure freely dissolved concentrations (C w,free) of lauryl diethanolamine (C12-DEA). C12-DEA can be protonated and act as a cationic surfactant. From the pH-dependent sorption to neutral SPME coatings (polyacrylate and PDMS), a pK a of 8.7 was calculated, which differs more than two units from the value of 6.4 reported elsewhere. Polyacrylate coated SPME could not adequately sample largely protonated C12-DEA in humic acid solutions of pH 6. A new hydrophobic SPME coating with cation-exchange properties (C18/SCX) sorbed C12-DEA 100 fold stronger than polyacrylate, because it specifically sorbs protonated C12-DEA species. The C18/SCX-SPME fiber showed linear calibration isotherms in a concentration range of <1nM–1μM (well below the CMC). Using the C18/SCX-SPME fibers, linear sorption isotherms to Aldrich humic acid at pH 6 (ionic strength 0.015M) were measured over a broad concentration range with a sorption coefficient of 10^5.3.

Molecularly imprinted polymers for the isolation of bioactive naphthoquinones from plant extracts

17 October 2013, 09:29:13

Publication date: 8 November 2013
Source:Journal of Chromatography A, Volume 1315
Author(s): Stella K. Tsermentseli , Panagiotis Manesiotis , Andreana N. Assimopoulou , Vassilios P. Papageorgiou
Molecularly Imprinted Polymers (MIPs) targeting shikonin, a potent antioxidant and wound healing agent, have been prepared using methacrylic acid (MAA) and 2-diethylaminoethyl methacrylate (DEAEMA) as functional monomers. An investigation of solution association between shikonin and both acidic and basic functional monomers by UV–vis titrations, suggested stronger affinity towards the basic functionality. Strong inhibition of the co-polymerisation reaction of such basic monomers was observed, but was overcome by reduction of the amount of template used during polymer synthesis. Polymer morphology was severely impacted by the template's radical scavenging behaviour as demonstrated by solid state NMR spectroscopy measurements. HPLC evaluation of the final materials in polar conditions revealed limited imprinting effects and selectivity, with the MAA polymers exhibiting marginally better performance. During application of the polymers as MI-SPE sorbents in non-polar solvents it was found that the DEAEMA based polymer was more selective towards shikonin compared to the MAA counterpart, while shikonin recoveries of up to 72% were achieved from hexane solutions of a commercial sample of shikonin, hexane extract of Alkanna tinctoria roots and a commercial pharmaceutical ointment.

Stir bar sorptive extraction with gas chromatography–mass spectrometry for the determination of resveratrol, piceatannol and oxyresveratrol isomers in wines

17 October 2013, 09:29:13

Publication date: 8 November 2013
Source:Journal of Chromatography A, Volume 1315
Author(s): J.I. Cacho , N. Campillo , P. Viñas , M. Hernández-Córdoba
A simple and highly sensitive procedure based on stir bar sorptive extraction coupled to gas chromatography–mass spectrometry by means of a thermal desorption unit (SBSE-TD-GC–MS) has been optimized for the determination of cis/trans isomers of resveratrol, piceatannol and oxyresveratrol in wine samples. Quantification of the cis-isomers was carried out by generating the standards from the corresponding trans-species once they had been preconcentrated on the SBSE extracting phase. The optimization of the acetylation derivatization, SBSE extraction and thermal desorption steps was investigated using Plackett–Burman designs, taking into account the high number of variables to be considered. The use of bisphenol F as internal standard allowed quantification of the samples against aqueous standards. Repeatability, expressed as relative standard deviation of 10 successive analyses was between 5% and 9%, confirming the high precision attained under the optimized conditions. Satisfactory recovery values of between 79% and 109% were obtained for spiked samples in the 0.2–1.0μgL⁻¹ concentration range, depending on the compound. The main compound determined in the analyzed samples was trans-resveratrol, with concentrations in the range of 3–230μgL⁻¹, depending on the type of wine.

Construction of graphene oxide magnetic nanocomposites-based on-chip enzymatic microreactor for ultrasensitive pesticide detection

17 October 2013, 09:29:13

Publication date: 8 November 2013
Source:Journal of Chromatography A, Volume 1315
Author(s): Ru-Ping Liang , Xiao-Ni Wang , Chun-Ming Liu , Xiang-Ying Meng , Jian-Ding Qiu
A new strategy for facile construction of graphene oxide magnetic nanocomposites (GO/Fe3O4 MNCs)-based on-chip enzymatic microreactor and ultrasensitive pesticide detection has been proposed. GO/Fe3O4 MNCs were first prepared through an in situ chemical deposition strategy. Then, acetylcholinesterase (AChE) was adsorbed onto the GO/Fe3O4 surface to form GO/Fe3O4/AChE MNCs which was locally packed into PDMS microchannel simply with the help of external magnetic field to form an on-chip enzymatic microreactor. The constructed GO/Fe3O4/AChE MNCs-based enzymatic microreactor not only have the magnetism of Fe3O4 NPs that make them conveniently manipulated by an external magnetic field, but also have the larger surface and excellent biocompatibility of graphene which can incorporate much more AChE molecules and well maintain their biological activity. On the basis of the AChE inhibition principle, a novel on-chip enzymatic microreactor was constructed for analyzing dimethoate which is usually used as a model of organophosphorus pesticides. Under optimal conditions, a linear relationship between the inhibition rates of AChE and the concentration of dimethoate from 1 to 20μgL⁻¹ with a detection limit of 0.18μgL⁻¹ (S/N=3) was obtained. The developed electrophoretic and magnetic-based chip exhibited excellent reproducibility and stability with no decrease in the activity of enzyme for more than 20 repeated measurements over one week period, which provided a new and promising tool for the analysis of enzyme inhibitors with low cost and excellent performance.

Simultaneous determination of polycyclic aromatic hydrocarbons and their chlorination by-products in drinking water and the coatings of water pipes by automated solid-phase microextraction followed by gas chromatography–mass spectrometry

17 October 2013, 09:29:13

Publication date: 8 November 2013
Source:Journal of Chromatography A, Volume 1315
Author(s): Jocelyn Tillner , Caroline Hollard , Cristina Bach , Christophe Rosin , Jean-François Munoz , Xavier Dauchy
In this study, an automated method for the simultaneous determination of polycyclic aromatic hydrocarbons (PAHs) and their chlorination by-products in drinking water was developed based on online solid-phase microextraction-gas chromatography–mass spectrometry. The main focus was the optimisation of the solid-phase microextraction step. The influence of the agitation rate, type of fibre, desorption time, extraction time, extraction temperature, desorption temperature, and solvent addition was examined. The method was developed and validated using a mixture of 17 PAHs, 11 potential chlorination by-products (chlorinated and oxidised PAHs) and 6 deuterated standards. The limit of quantification was 10ng/L for all target compounds. The validated method was used to analyse drinking water samples from three different drinking water distribution networks and the presumably coal tar-based pipe coatings of two pipe sections. A number of PAHs were detected in all three networks although individual compositions varied. Several PAH chlorination by-products (anthraquinone, fluorenone, cyclopenta[d,e,f]phenanthrenone, 3-chlorofluoranthene, and 1-chloropyrene) were also found, their presence correlating closely with that of their respective parent compounds. Their concentrations were always below 100ng/L. In the coatings, all PAHs targeted were detected although concentrations varied between the two coatings (76–12,635mg/kg and 12–6295mg/kg, respectively). A number of chlorination by-products (anthraquinone, fluorenone, cyclopenta[d,e,f]phenanthrenone, 3-chlorofluoranthene, and 1-chloropyrene) were also detected (from 40 to 985mg/kg), suggesting that the reaction of PAHs with disinfectant agents takes place in the coatings and not in the water phase after migration.

Determination of haloacetic acids in swimming pool waters by membrane-protected micro-solid phase extraction

17 October 2013, 09:29:13

Publication date: 8 November 2013
Source:Journal of Chromatography A, Volume 1315
Author(s): Hakimu Nsubuga , Chanbasha Basheer
In this study, a simple and efficient extraction method for determining haloacetic acids (HAAs) in swimming pool waters has been developed. HAAs are toxic organic pollutants of disinfection origin most commonly detected in swimming pool and drinking waters at trace level concentrations. For the first time, a highly efficient sorbent was developed using rice husk and used for micro-solid phase extraction (μ-SPE) technique. To increase the extraction capability of rice husk silica, iron oxide was incorporated via sol–gel process. In μ-SPE device, the novel sorbent was packed and used for extraction of HAAs prior to analysis using ultra performance liquid chromatography–ultraviolet detection (UPLC–UV). Various extraction parameters were optimized to improve the extraction efficiency of μ-SPE. Under optimum conditions, linearity (coefficient of determination, r ² ≥0.991 over the concentration range of 1–150μg/L), detection limits in the range of 0.001–0.092μg/L, mean recoveries up to 110% with corresponding relative standard deviations of 2–7% (n =3) had been obtained. Finally, the method was applied to swimming pool water to evaluate its feasibility. The mean concentrations for HAAs from the pool waters were in the range of 6.8 and 48.6μg/L which are far below the standard values set by United States Environmental Protection Agency.

Statistical evaluation of the influence of soil properties on recoveries and matrix effects during the analysis of pharmaceutical compounds and steroids by quick, easy, cheap, effective, rugged and safe extraction followed by liquid chromatography–tandem mass spectrometry

17 October 2013, 09:29:13

Publication date: 8 November 2013
Source:Journal of Chromatography A, Volume 1315
Author(s): Marie-Virginie Salvia , Cécile Cren-Olivé , Emmanuelle Vulliet
Numerous chemical products are dispersed in our environment. Many of them are recognized as harmful to humans and the ecosystem. Among these harmful substances are antibiotics and steroid hormones. Currently, very few data are available on the presence and fate of these substances in the environment, in particular for solid matrices, mainly due to a lack of analytical methodologies. Indeed, soil is a very complex matrix, and the nature and composition of the soil has a significant impact on the extraction efficiency and the sensitivity of the method. For this reason a statistical approach was performed to study the influence of soil parameters (clay, silt, sand and organic carbon percentages and cation exchange capacity (CEC)) on recoveries and matrix effects of various pharmaceuticals and steroids. Thus, an analysis of covariance (ANCOVA) was performed when several substances were analyzed simultaneously, whereas a Pearson correlation was used to study the compounds individually. To the best of our knowledge, this study is the first time such an experiment was performed. The results showed that clay and organic carbon percentages as well as the CEC have an impact on the recoveries of most of the target substances, the variables being anti-correlated. This result suggests that the compounds are trapped in soils with high levels of clay and organic carbon and a high CEC. For the matrix effects, it was shown that the organic carbon content has a significant effect on steroid hormones and penicillin G matrix effects (positive correlation). Finally, interaction effects (first order) were evaluated. This latter point corresponds to the crossed effects that occur between explanatory variables (soil parameters). Indeed, the value taken by an explanatory variable can have an influence on the effect that another explanatory variable has on a dependent variable. For instance, it was shown that some parameters (silt, sand) have an impact on the effect that clay content has on recoveries. Besides, CEC and silt affect the influence that organic carbon percentage has on matrix effect. This original approach provides a better understanding of the complex interactions that occur in soil and could be useful to understand and predict the performance of an analytical method.

Preparation of titanium-grafted magnetic mesoporous silica for the enrichment of endogenous serum phosphopeptides

17 October 2013, 09:29:13

Publication date: 8 November 2013
Source:Journal of Chromatography A, Volume 1315
Author(s): Xiao-Shui Li , Ya-Ni Pan , Yong Zhao , Bi-Feng Yuan , Lin Guo , Yu-Qi Feng
As one of the most important post-translational modifications, reversible phosphorylation of protein plays crucial roles in a large number of biological processes. Moreover, endogenous phosphopeptides are also associated with certain human diseases. An efficient enrichment and separation method is the premise for successful identification and quantification of phosphopeptides. In this work, titanium grafted magnetic mesoporous silica (Fe3O4@Ti-mSiO2) was developed and applied for the enrichment of endogenous phosphopeptides. Fe3O4@Ti-mSiO2 particles were prepared by grafting titanocene dichloride on the inner walls of magnetic mesoporous silica and then being calcined to remove cyclopentadienyl ligand. The physicochemical properties of the prepared materials were characterized by energy dispersive X-ray spectroscopy (EDX), nitrogen adsorption–desorption analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). For selective enrichment of phosphopeptides, the prepared Fe3O4@Ti-mSiO2 particles were applied for tryptic digests of β-casein, mixtures of β-casein and bovine serum albumin (BSA), and low-fat milk. Finally, Fe3O4@Ti-mSiO2 was successfully applied for the enrichment of endogenous phosphopeptides from human serum.

Multi-stir bar sorptive extraction for analysis of odor compounds in aqueous samples

17 October 2013, 09:29:13

Publication date: 8 November 2013
Source:Journal of Chromatography A, Volume 1315
Author(s): Nobuo Ochiai , Kikuo Sasamoto , Teruyo Ieda , Frank David , Pat Sandra
As reproducible coating of stir bars with more polar phases was found to be very difficult, a supporting grid was used in the development of an ethyleneglycol-modified Silicone (EG Silicone) coated stir bar. This new polar coating showed good performance for the extraction of polar solutes, but long term use also showed degradation of the coating due to friction while stirring. In order to address the lower robustness of the EG Silicone stir bar which has a much softer coating compared to a conventional polydimethylsiloxane (PDMS) stir bar, a novel SBSE procedure termed multi-SBSE ( ^m SBSE) was developed. ^m SBSE consists of the robust PDMS stir bar stirring at the bottom of the vial and the EG Silicone stir bar attached on the inner side wall of the vial (a magnetic clip is used for the set-up). After extraction, the two stir bars are placed in a single glass desorption liner and are simultaneously thermally desorbed. The desorbed compounds were analyzed by thermal desorption–gas chromatography–mass spectrometry (TD–GC–MS). Compared to conventional SBSE, ^m SBSE provides more uniform enrichment of a wide range of odor compounds in aqueous sample since both stir bars can complement each other, while eliminating the damage of the EG Silicone phase during the extraction. The robustness of the EG Silicone stir bar was dramatically increased and more than 30 extraction and desorption cycles were possible without loss in performance. The recoveries for polar solutes such as 2-acetyl pyrrole (log K ow: 0.55), benzyl alcohol (log K ow: 1.08), guaiacol (log K ow: 1.34), and indole (log K ow: 2.05) were increased by a factor of about 2–7. The ^m SBSE–TD–GC–MS method showed good linearity (r ² >0.9913) and high sensitivity (limit of detection: 0.011–0.071ngmL⁻¹) for the test compounds spiked in water. The feasibility and benefit of the method was demonstrated with analysis of odor compounds in roasted green tea. The normalized areas obtained from ^m SBSE showed the best enrichment for most of the selected compounds compared to conventional SBSE using the PDMS stir bar or the EG Silicone stir bar. Fifteen compounds were determined in the range of 0.15–210ngmL⁻¹ (RSD<14%, n =6).