Just Published: Journal of Chromatography A

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Journal of Chromatography A

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Selected papers from the latest issue:

Investigation of the ultrasound effect and target analyte selectivity of dispersive liquid–liquid microextraction and its application to a quinocetone pharmacokinetic study

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Jiaheng Zhang, Min Li, Linxia Li, Yubo Li, Bing Peng, Suxia Zhang, Haixiang Gao, Wenfeng Zhou
An ultrasound-assisted dispersive liquid–liquid microextraction (UADLLME) was developed as a simple, sensitive, and robust method for the simultaneous determination of quinocetone (QCT) and three of its synthesized desoxy metabolites in swine urine samples via high-performance liquid chromatography (HPLC). Experimental parameters were optimized using the one-factor-at-a-time approach and were followed using an orthogonal array design. The results indicate that ultrasonic irradiation significantly affects the DLLME extraction efficiency. Moreover, the intermolecular binding energies and octanol–water partition ratio (K ow) of the target analytes were calculated using the density functional theory and the atom-additive method, respectively. A high correlation was found between the extraction efficiency and the calculated results, which may serve as a scientific guideline in the determination of the target analyte selectivity of DLLME. The feasibility of UADLLME with HPLC for the simultaneous determination of QCT and its desoxy metabolites in blank swine urine samples was then investigated. Higher enrichment factors (118–175), low limits of detection (0.06–0.12ngmL⁻¹), and high precisions (relative standard deviation < 2.5%) were obtained. Calibration curves were performed in the 0.5–500ngmL⁻¹ range and displayed good linearity. In addition, the proposed method was successfully applied to the pharmacokinetic study of QCT and its desoxy metabolites in real urine samples. The results show that UADLLME has a potential application in the pharmacokinetic and residue studies of quinoxaline-N-dioxides derivatives in biological fluid samples.

Highlights

► Ultrasound-assisted (UA) DLLME was used for determination of Quinoxaline-N-dioxide drugs in swine urine samples. ► Orthogonal array design was performed to evaluated experimental parameters. ► Calculated intermolecular binding energies and K ow were obtained to investigate target analyte selectivity.

Substrateless graphene fiber: A sorbent for solid-phase microextraction

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Yan-Bo Luo, Bi-Feng Yuan, Qiong-Wei Yu, Yu-Qi Feng
In current study, a substrateless graphene fiber was successfully prepared by a simple hydrothermal strategy and used as solid-phase microextraction (SPME) sorbent. Five organochlorine pesticides (OCPs) were employed as model analytes to evaluate the performance of as-prepared graphene fiber. The results showed that the graphene fiber exhibited higher extraction efficiencies, higher thermal stability (up to 310°C), better reproducibility, and longer service life (more than 180 times reuse) than commercial fibers. In addition, the method for the determination of OCPs was proposed by coupling headspace (HS)-SPME technique with gas chromatography/electron capture detector (HS-SPME-GC/ECD). The proposed HS-SPME-GC/ECD method showed low limits of detection (0.83–11.5ng/L), wide linear dynamic ranges (more than 2 orders of magnitude), and acceptable reproducibility (RSD<10.9%). Finally, the proposed method was successfully applied to the analysis of OCPs in environmental water samples with good recoveries (81–121%) and satisfactory precisions (RSD<9%).

Highlights

► A graphene fiber was successfully prepared by a simple hydrothermal strategy. ► The graphene fiber was used as sorbent of solid-phase microextraction. ► The graphene fiber exhibited higher thermal stability and longer lifetime than commercial fibers. ► The graphene fiber shows higher enrichment capability for OCPs than PDMS fiber. ► The graphene fiber was used to determine OCPs in environmental water samples.

Novel double-confined polymeric ionic liquids as sorbents for solid-phase microextraction with enhanced stability and durability in high-ionic-strength solution

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Juanjuan Feng, Min Sun, Lili Xu, Shuai Wang, Xia Liu, Shengxiang Jiang
Because of the occurrence of ion exchange between high-ionic-strength solution and anions of polymeric ionic liquids (PILs), PILs based solid-phase microextraction (SPME) fibers were rarely used in direct immersion mode to high-salt-added samples. In this work, a novel double-confined PIL sorbent was prepared by co-polymerization of cation and anion of 1-vinyl-3-octylimidzaolium p-styrenesulfonate (VOIm⁺SS⁻). The poly(VOIm⁺-SS⁻) was chemically bonded onto functionalized stainless steel wire via surface radical chain-transfer reaction. Stability of poly(VOIm⁺-SS⁻) in high-ionic-strength solution was investigated and compared with that of poly(1-vinyl-3-octylimidzaolium benzenesulfonate) (poly(VOIm⁺BS⁻)) by elemental analysis of sulfur element, and results turned out that the poly(VOIm⁺-SS⁻) was more stable. Coupled to gas chromatography (GC), the poly(VOIm⁺-SS⁻) fiber was used to extract three sorts of compounds including anilines, phenols and phthalate esters in aqueous solution. The as-established method showed good linearity, low detection limits, and acceptable repeatability. The direct immersion SPME-GC method was applied to determine the model phthalate esters in bottled mineral water. The determination results were satisfactory.

Highlights

► Cation and anion of IL were copolymerized in situ on functionalized metal support. ► Stability of the PIL fiber in salted solution was enhanced by copolymerization. ► The copolymerized PILs SPME fiber was successfully used in direct immersion mode.

Analysis of fatty alcohol derivatives with comprehensive two-dimensional liquid chromatography coupled with mass spectrometry

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Victoria Elsner, Sabrina Laun, David Melchior, Michael Köhler, Oliver J. Schmitz
A simultaneous separation of anionic (fatty alcohol sulfates, fatty alcohol ether sulfates), non-ionic (alkyl polyglucosides, fatty alcohol ethoxylates) and amphoteric (cocamidopropyl betaines) surfactants was performed by comprehensive two-dimensional liquid chromatography (LCxLC) utilizing a ZIC^®-HILIC column in the first dimension, a Reprosphere 100 C8-Aqua column in the second dimension and a 10-port two position valve as the interface. The volume of the two sample loops were 25 or 50μL and allow a one or two minute modulation at a 25μL/min flow rate. In the first dimension, a gradient of acetonitrile and an ammonium acetate buffer was used to separate polyethoxylated surfactants by their degree of ethoxylation (EO number) whereas in the second dimension, a separation by alkyl chain was performed using a methanol/ammonium acetate buffer gradient. A baseline separation of the above mentioned surfactants according to both EO number and alkyl chain was achieved. The best performance was used to compare two different LCxLC–QTOF MS systems, which demonstrate that a transfer of the method from one system to a totally different system is possible. However, because of the differences in delay volume and extra-column volume between these systems the separation power is changed.

Highlights

► Simultaneous separation of anionic, non-ionic and amphoteric surfactants was performed by LCxLC. ► A baseline separation of surfactants according to both EO number and alkyl chain was achieved. ► The best performance was used to compare two different LCxLC–QTOF MS systems.

Extending the detection window of diazepam by directly analyzing its glucuronide metabolites in human urine using liquid chromatography–tandem mass spectrometry

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Xin Wang, Rong Wang, Yurong Zhang, Chen Liang, Haiying Ye, Fangqi Cao, Yulan Rao
A method for the simultaneous direct analysis of diazepam oxazepam glucuronide, temazepam glucuronide, oxazepam, nordiazepam, and temazepam in human urine was developed and validated. Urine sample was purified by solid phase extraction (SPE), and the analysis was achieved using a liquid chromatography–tandem mass spectrometry (LC–MS/MS) system equipped with an electrospray ionization source (ESI). Multiple reaction monitoring (MRM) mode was used to analyze the target compounds. Extraction recoveries were 65–122% for all the analytes. The method showed acceptable intra–assay and inter–assay precision (both relative standard deviation (RSD)≤11.2%) for quality control (QC) samples. The limits of detections (LODs) were in the range of 0.1–2ng/mL. The present assay was applied to analyze the urine obtained from three volunteers after oral administration of a single dose 5mg of diazepam. The results showed that, the detection periods of oxazepam glucuronide and temazepam glucuronide were much longer than diazepam and other metabolites.

Highlights

► A LC–MS/MS method was developed for analyzing diazepam and its metabolites in urine. ► Glucuronides of diazepam in urine were analyzed without enzymatic or acid hydrolysis. ► LODs (0.1–2ng/mL) of diazepam and its metabolites demonstrated high sensitivity. ► Urine of three volunteers after orally administrated 5mg of diazepam was analyzed. ► Detection window of diazepam in urine was extended by detecting its glucuronides.

Liquid chromatography tandem mass spectrometry method for characterization of monoaromatic nitro-compounds in atmospheric particulate matter

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Zoran Kitanovski, Irena Grgić, Reinhilde Vermeylen, Magda Claeys, Willy Maenhaut
Nitrogen-containing organic compounds in the atmosphere have drawn attention owing to their impact on aerosol chemistry and physics and their potential adverse effects on the biosphere. Among them, nitrocatechols and their homologs have recently been associated with biomass burning. In the present study, nitrocatechols, nitrophenols, nitroguaiacols and nitrosalicylic acids (NSAs) were simultaneously quantified for the first time by using a new analytical method based on liquid chromatography/tandem mass spectrometry, which was systematically optimized and validated. Several analyte specific issues regarding the sample preparation and chromatographic analysis were addressed in order to ensure method sensitivity, precision, and accuracy. Sample matrix effects were thoroughly investigated in order to ensure method specificity. The method was found to be sensitive with limits of detection ranging from 0.1 to 1.0μgL⁻¹, and with accuracy generally between 90 and 104%. The relative standard deviations for repeatability and intermediate precision were better than 4% and 9%, respectively. The method was applied to the analysis of winter and summer PM10 samples from the city of Ljubljana, Slovenia. Aerosol concentrations as high as 152 and 134ngm⁻³ were obtained for the major aerosol nitro-aromatics: 4-nitrocatechol (4NC) and methyl-nitrocatechols (MNCs), respectively. Up to 500-times higher concentrations of 4NC and MNCs were found in winter compared to summer aerosols. The correlation analysis for winter samples showed that 4NC, MNCs, and NSAs are strongly inter-correlated (R ² =0.84–0.96). Significant correlations between these analytes and anhydrosugars support their proposed origin from biomass burning. The studied nitro-aromatics were found to constitute a non-negligible fraction (around 1%) of the organic carbon.

Highlights

► Development of HPLC–MS/MS method for simultaneous quantification of 12 nitro-aromatics. ► Validation of the method for analysis of atmospheric particulate matter. ► Detailed investigation of matrix effects. ► Significantly higher concentrations of nitrocatechols in winter samples. ► Correlation analysis between nitro-aromatics and anhydrosugars.

Application of the van’t Hoff dependences in the characterization of molecularly imprinted polymers for some phenolic acids

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Natalia Denderz, Jozef Lehotay
Thermodynamic analysis was used to quantify the contribution of entropic and enthalpic terms of the binding processes of selected phenolic acids (PAs), quercetin and diperodon on series of molecularly imprinted polymers (MIPs). All polymers were prepared using acrylamide as functional monomer and acetonitrile as a porogen. The following PAs were used as templates – gallic (GA), gentisic (GeA), syringic (SyrA), protocatechuic (PCA), 4-hydroxybenzoic (pHBA) and vanillic (VA). The assessment was based on quantification by HPLC measurement of the analytes tested at temperature range from 20°C to 60°C in two mobile phases – methanol and porogen. There were determined van’t Hoff curves – dependences between logarithms of the retention factors (ln k) and the inverse value of the temperature (1/T). All plots fall along straight lines, what suggests that there were no changes in the sorption mechanisms over the studied temperature range. Determined thermodynamic characteristics helped to specify the nature of molecular recognition on the PAs-MIPs. We found that preferred eluent for analytes sorption on the PAs-MIPs and the NIP was porogen. When methanol as the mobile phase was used there was not documented sorption of the investigated compounds on the NIP. Calculated imprinting factors (IFs) in porogen were highest in the dominant advantage of template molecules used, what confirmed a good molecular imprinting effect. The IF values for PAs studied were as follows: GA=21.98±2.62, PCA=6.07±0.13, pHBA=3.58±0.25, SyrA=2.80±0.17, GeA=2.37±0.34 and VA=2.07±0.10. The results of thermodynamic studies demonstrated that enthalpic term was the dominating driving force for the predominant part of investigated analytes. The exceptions were: SyrA on the NIP and on the GA-MIP, diperodon on the PCA-MIP in acetonitrile and quercetin on the GA-MIP in methanol where a favourable driving force was to be found an entropic term. The PAs-MIPs and NIP were also characterized by attenuated total reflectance analysis Fourier transform infrared spectroscopy (ATR-FTIR) and scanning electron microscopy (SEM).

Highlights

► Thermodynamic study of the phenolic acids-MIPs compared to the NIP. ► Study of the PAs-MIPs selectivity towards structurally similar PAs, quercetin and diperodon. ► PAs-MIPs and NIP characterization by ATR-FTIR and SEM analyses.

Influence of particle properties on the wall region in packed capillaries

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Stefan Bruns, Daniela Stoeckel, Bernd M. Smarsly, Ulrich Tallarek
Analytical columns (4.6mm i.d.) packed with core–shell particles have shown a significantly reduced eddy dispersion contribution to band broadening compared to conventional fully porous particles. It has been speculated if this is caused by the narrow particle size distribution (PSD) of the core–shell particles, as an intrinsic advantage, or by an improved packing structure that specifically reduces the transcolumn velocity biases caused by wall effects. A recent simulation study has pointed against the former proposition [A. Daneyko et al., Anal. Chem. 83 (2011) 3903]. It is more likely that the slurry packing process for core–shell particles results in bed morphologies with reduced wall effects compared to the fully porous particles with a wide PSD. To access the latter proposition experimentally we slurry packed capillary columns (100μm i.d.) with different fully porous (wide PSDs) and core–shell (narrow PSDs) particles and imaged their bed structures three-dimensionally using confocal laser scanning microscopy. This allowed us to resolve and analyze the bed morphology in these columns locally on all length scales contributing to eddy dispersion. On the transcolumn scale we observed a systematic difference between core–shell and fully porous particles: In the vicinity of the column wall the core–shell particles packed denser (closer to the bulk packing densities) and with a higher regularity than the fully porous particles. The bulk regions of all packings were effectively indistinguishable. This provides experimental evidence that the reduced eddy dispersion contribution with core–shell packings should be attributed to a higher transcolumn homogeneity rather than to an improved bed morphology on smaller length scales, e.g., to a reduced short-range disorder.

Highlights

► Slurry packed capillaries are reconstructed using confocal laser scanning microscopy. ► Their bed morphology is analyzed by chord length distributions and porosity profiles. ► Different size distributions of core–shell and fully porous particles are in the focus. ► Core–shell particles show an improved bed morphology next to the column wall. ► The bulk packing regions of all columns are effectively indistinguishable.

Quantification of achiral and chiral methylsulfonyl polychlorinated biphenyl metabolites by column-switching liquid chromatography–atmospheric pressure photoionization–tandem mass spectrometry

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Victoria I. Cooper, Robert J. Letcher, Rune Dietz, Christian Sonne, Charles S. Wong
An enantioselective heart-cut column-switching liquid chromatography–atmospheric pressure photoionization–tandem mass spectrometry method was developed for the analysis of 25 methylsulfonyl polychlorinated biphenyl metabolites in tissue extracts. Use of a pyrenyl-ethyl silica column in the first dimension enabled separation of all but two pairs of isobaric analytes. Enantioseparation was achieved for 9 out of the 10 atropisomeric analytes using a Chiralpak AD-H amylose-based column within 93min, resulting in greater chromatographic resolution of enantioseparation over shorter analysis time by up to a factor of three, compared to previous one-dimensional and multi-dimensional gas chromatography-based methods. Precision for concentration and enantiomer fraction measurements was within 11% and 3% relative standard deviation, respectively. Limits of detection ranged from 0.01 to 1.73ng on-column. Meta-congeners had poorer sensitivity (i.e., ng on-column), consistent with existing gas chromatography-based methods. Despite this limitation, the method was successfully applied to the analysis of Greenland sledge dog adipose tissue extracts, which had highly non-racemic residues of 4-methylsulfonyl-2,2′,3,5′,6-pentachlorobiphenyl and 4′-methylsulfonyl-2,2′,3,3′,4,6′-hexachlorobiphenyl, consistent with past reports in Arctic mammals.

Highlights

► A novel method was created to quantify methylsulfonyl PCBs and their atropisomers. ► First time PYE column used to fractionate methylsulfonyl PCBs. ► First use of APPI and column-switching LC for quantifying achiral and chiral congeners. ► Analysis time was up to three times less than existing gas chromatography methods. ► Highly non-racemic methylsulfonyl PCBs were found in sledge dogs fed whale blubber.

Multiresidue analysis of 88 polar organic micropollutants in ground, surface and wastewater using online mixed-bed multilayer solid-phase extraction coupled to high performance liquid chromatography–tandem mass spectrometry

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Sebastian Huntscha, Heinz P. Singer, Christa S. McArdell, Carolin E. Frank, Juliane Hollender
An automated multiresidue method consisting of an online solid-phase extraction step coupled to a high performance liquid chromatography–tandem mass spectrometer (online-SPE–HPLC–MS/MS method) was developed for the determination of 88 polar organic micropollutants with a broad range of physicochemical properties (log D OW (pH 7): −4.2 to 4.2). Based on theoretical considerations, a single mixed-bed multilayer cartridge containing four different extraction materials was composed for the automated enrichment of water samples. This allowed the simultaneous analysis of pesticides, biocides, pharmaceuticals, corrosion inhibitors, many of their transformation products, and the artificial sweetener sucralose in three matrices groundwater, surface water, and wastewater. Limits of quantification (LOQs) were in the environmentally relevant concentration range of 0.1–87ng/L for groundwater and surface water, and 1.5–206ng/L for wastewater. The majority of the compounds could be quantified below 10ng/L in groundwater (82%) and surface water (80%) and below 100ng/L in wastewater (80%). Relative recoveries were largely between 80 and 120%. Intraday and inter-day precision, expressed as relative standard deviation, were generally better than 10% and 20%, respectively. 50 isotope labeled internal standards were used for quantification and accordingly, relative recoveries as well as intraday and inter-day precision were better for compounds with corresponding internal standard. The applicability of this method was shown during a sampling campaign at a riverbank filtration site for drinking water production with travel times of up to 5 days. 36 substances of all compound classes investigated could be found in concentrations between 0.1 and 600ng/L. The results revealed the persistence of carbamazepine and sucralose in the groundwater aquifer as well as degradation of the metamizole metabolite 4-acetamidoantipyrine.

Highlights

► We developed a new online-SPE–HPLC–MS/MS method for polar organic micropollutants. ► Four different SPE materials were combined in one multiple use enrichment cartridge. ► 88 compounds of different classes and physicochemical properties are included. ► LOQs, recoveries and precision were good for ground, surface and wastewater. ► The method was applied during a field campaign at a riverbank filtration site.

Multiclass screening method based on solvent extraction and liquid chromatography–tandem mass spectrometry for the determination of antimicrobials and mycotoxins in egg

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Anna Laura Capriotti, Chiara Cavaliere, Susy Piovesana, Roberto Samperi, Aldo Laganà
A QuEChERS (Quick Easy Cheap Effective Rugged Safe)-like extraction method was developed for the simultaneous analysis of veterinary drugs and mycotoxins in hen eggs by liquid chromatography–tandem mass spectrometry (LC–MS/MS) with electrospray (ESI) source. Various classes of antimicrobials (tetracyclines, ionophores, coccidiostats, penicillins, cephalosporins, fluoroquinolones, sulfonamides) and mycotoxins (enniatins, beauvericin, ochratoxins, aflatoxins) were considered for the development of this method. Particular attention was devoted to extraction optimization: different solvents (acetone, acetonitrile and methanol), different pH values and different sample to extracting volume ratios were tested and evaluated in terms of recovery, relative standard deviation (RSD) and ESI signal suppression due to matrix effect. Chromatographic and mass spectrometric conditions were optimized to obtain the best instrumental performances for most of the analytes. Quantitative analysis was performed by means of matrix-matched calibration, in a range that varied depending on the analyte and its established maximum limit, when there was one. Recoveries at 100μgkg⁻¹ spiking level were >62% (3<RSD<17) for all the antimicrobials except lasalocid A (41±10%) and oxacillin (56±17%). The multiclass method proposed is rapid, simple, and involves a low solvent consumption, in line with QuEChERS features and modern analytical requirements.

Highlights

► Simultaneous determination of antimicrobials and mycotoxins in egg. ► Evaluation of extraction conditions by factorial experimental design. ► Simple QuEChERS-like extraction with low cost, solvent consumption and analysis time.

Optimization of comprehensive two-dimensional gradient chromatography coupling in-line hydrophilic interaction and reversed phase liquid chromatography

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Pavel Jandera, Tomáš Hájek, Magda Staňková, Kateřina Vyňuchalová, Petr Česla
In-line coupled comprehensive HILIC×RP systems should offer larger selectivity differences and better two-dimensional orthogonality than coupled RP×RP systems. However, this may not apply for all systems. The HILIC selectivity depends on the mix of selective polar and non-polar interactions with the functional groups, but also with the matrix of polar columns and depends on the sample type. We synthesized a new polar monolithic sulfobetaine polymethacrylate capillary column with excellent efficiency for low-molecular compounds. When used in the first, HILIC dimension coupled to core–shell or monolithic RP columns in the second dimension, this column provides much improved orthogonality for two-dimensional separations of phenolic and flavonoid compounds, in comparison to silica-bonded Diol, Polyethylene glycol or Zwitterionic columns. We investigated the performance of 11 short 5cm and 3cm columns for fast (1–2min) gradient second-dimension separations. Band broadening or distortion may occur in directly coupled comprehensive HILIC×RP systems, due to strong solvent-strength differences between the mobile phases used in the first and in the second dimension. To suppress this effect, low fraction volumes were collected from a 0.5mm I.D. capillary monolithic sulfobetaine column at the flow-rate of a few microliters per min, coupled in-line with various core–shell columns operated at the maximum flow-rate. This setup with simultaneous gradient elution in the HILIC and in the RP dimension provided successful separation of natural antioxidants.

Highlights

► Various commercial core–shell columns are suitable for HILIC×RP 2D separations. ► A new efficient thermally stable capillary monolithic HILIC column was prepared. ► The capillary zwitterionic HILIC column is suitable for orthogonal 2D separations. ► Solvent strength incompatibility causes band broadening in HILIC×RP systems. ► Capillary columns in the first dimension and small fractions improve compatibility.

Isoform separation and binding site determination of mono-PEGylated lysozyme with pH gradient chromatography

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Benjamin Maiser, Frieder Kröner, Florian Dismer, Gerald Brenner-Weiß, Jürgen Hubbuch
Covalent attachment of PEG to proteins, known as PEGylation, is currently one of the main approaches for improving the pharmacokinetics of biopharmaceuticals. However, the separation and characterization especially of positional isoforms of PEGylated proteins are still challenging tasks. A common purification strategy uses ion exchange chromatography with increasing ionic strength by shallow salt gradients. This paper presents a method which applies a linear pH gradient chromatography to separate five of six possible isoforms of mono-PEGylated lysozyme, modified with 5kDa and 10kDa mPEG-aldehyde. To identify the corresponding PEGylation sites a comparison of elution pH values and calculated isoelectric points of each isoform, was used. The resulting correlation showed an R ² >0.99. Fractionation, tryptic digestion and subsequent MALDI-MS analysis of each peak, verified the predicted elution order. Based on UV areas the N-terminal amine at lysine 1 exhibited the highest reactivity, followed by the lysine 33 residue.

Highlights

► High resolution separation of PEG-lysozyme isoforms using pH gradients. ► Significant increase in resolution compared to salt gradient runs demonstrated. ► In silico prediction and MALDI-MS validation of isoform identification.

Pesticide analysis in teas and chamomile by liquid chromatography and gas chromatography tandem mass spectrometry using a modified QuEChERS method: Validation and pilot survey in real samples

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Ana Lozano, Łukasz Rajski, Noelia Belmonte-Valles, Ana Uclés, Samanta Uclés, Milagros Mezcua, Amadeo R. Fernández-Alba
This paper presents the validation of a modified QuEChERS method in four matrices – green tea, red tea, black tea and chamomile. The experiments were carried out using blank samples spiked with a solution of 86 pesticides (insecticides, fungicides and herbicides) at four levels – 10, 25, 50 and 100μg/kg. The samples were extracted according to the citrate QuEChERS protocol; however, to reduce the amount of coextracted matrix compounds, calcium chloride was employed instead of magnesium sulphate in the clean-up step. The samples were analysed by LC–MS/MS and GC–MS/MS. Included in the scope of validation were: recovery, linearity, matrix effects, limits of detection and quantitation as well as intra-day and inter-day precision. The validated method was used in a real sample survey carried out on 75 samples purchased in ten different countries. In all matrices, recoveries of the majority of compounds were in the 70–120% range and were characterised by precision lower than 20%. In 85% of pesticide/matrix combinations the analytes can be detected quantitatively by the proposed method at the European Union Maximum Residue Level. The analysis of the real samples revealed that large number of teas and chamomiles sold in the European Union contain pesticides whose usage is not approved and also pesticides in concentrations above the EU MRLs.

Highlights

► A method for analysis of 86 pesticide residues in green, black, red teas and chamomile was validated. ► A modification of QuEChERS method was employed; calcium chloride in clean-up step. ► The method was applied to the real samples. ► Pesticides above EU maximum residue levels detected in real samples. ► Pesticides banned in EU detected in real samples.

Thermal Solid Sample Introduction–Fast Gas Chromatography–Low Flow Ion Mobility Spectrometry as a field screening detection system

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Saeed Hajialigol, Seyed Alireza Ghorashi, Amir Hossein Alinoori, Amir Torabpour, Mehdi Azimi
The potential of Thermal Solid Sample Introduction (TSSI)–Fast Gas Chromatography (GC)–Low Flow Ion Mobility Spectrometry (LF-IMS) having been designed and constructed in Engineering Research Center of Esfahan, detector group was investigated for chemical detection capabilities. Customizing the configuration of fast GC–IMS as a high technology, provides unique solutions for rapid detection of a broad range of chemical mixtures in many operational environments. TSSI configuration provides fast and easily applied method for direct detection with no additional sample preparation or extraction. The time required for total analysis, less than 265s, was determined by the wide range of solid matrixes, including nitrate esters, nitroaromatics, and a nitramine. The fast extraction together with the short separation time limits degradation of the thermally labile compounds and decreases the peak widths, which results in larger peak intensities and a simultaneous improvement in detection limits. For signal-to-noise ratio equals to 5, the detection limits for instrument for TNT, DNT and RDX were attained 15, 10 and 50ng/μl respectively. The combination of short analysis time and low detection limits make this instrument a potential candidate for field screening techniques.

Highlights

► Investigating the potential of home-made TSSI–GC–IMS for chemical detection. ► Rapid detection of various chemical mixtures in many operational environments. ► Field screening candidate due to combination of short analysis time and low LOD. ► TSSI provides direct detection with no additional sample preparation or extraction.

Room temperature ionic liquids: New GC stationary phases with a novel selectivity for flavor and fragrance analyses

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Cecilia Cagliero, Carlo Bicchi, Chiara Cordero, Erica Liberto, Barbara Sgorbini, Patrizia Rubiolo
Ionic liquids (ILs) are of great interest as moderately polar to polar stationary phases for GC, because their selectivity differs markedly from that of conventionally used phases. In the flavor, fragrance and essential oil fields, analysts often deal with complex mixtures of compounds having similar structural and physical characteristics (e.g., mono- and sesquiterpenoids), therefore requiring an interactive combination between chromatographic and mass spectral data for correct identification. New GC stationary phases with different selectivity must therefore be continually tested. Performance and evolution over time of commercially available IL columns versus those commonly used in these fields are here evaluated, mainly in view of their routine use. Chromatographic and separative properties (efficiency, separation capability, inertness and/or activity) of commercially available IL columns were compared to those of columns coated with 5% phenyl–95% methylpolysiloxane, 14% cyanopropyl–86% polysiloxane, and polyethylene glycol, on different complexity samples, including standard mixtures of volatile suspected allergens and pesticides, and cornmint and vetiver essential oils. The results show that IL columns can successfully be used for a wide range of applications characteristic of these fields, mainly because of their unusual selectivity, in particular when separations based on functional groups are required. Moreover, the latest generation of IL columns (IL61 and IL60) presents chromatographic performance comparable to or only slightly lower than that of the conventional columns routinely used in these fields.

Highlights

► Commercially available ionic liquids column performance were investigated. ► Their routine use for flavor, fragrance and essential oil fields was evaluated. ► Highly interesting selectivity for the above fields was found. ► Chromatographic performance similar to those of conventional columns were observed.

Macroporous polymer monoliths as second dimension columns in comprehensive two-dimensional gas chromatography: A feasibility study

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Daniela Peroni, Rudy J. Vonk, Wil van Egmond, Hans-Gerd Janssen
When the typical column combinations are used, comprehensive two-dimensional gas chromatography (GC×GC) suffers from the impossibility to operate both dimensions at their optimum carrier gas velocities at the same time. This as a result of the flow mismatch caused by the different dimensions of the columns used. The objective of the present study was the development of monolithic second dimension columns which would allow simultaneous optimum-velocity operation. With monolithic GC columns the optimum performance can be obtained at any given flow rate by varying the bed structure and column diameter. Different divinylbenzene-based monolithic columns were prepared and evaluated in terms of permeability and performance. Plate heights of less than 0.18mm and plate generation rates up to 600 plates/s were achieved. 1D-GC experiments performed on short monolithic columns showed a good resolving power thanks to the elevated retention and the good selectivity. A peak capacity up to 12 peaks per 4–5s was obtained for low-boiling alkanes, confirming the potential for fast separations. Excellent repeatability in terms of retention times (RSD<0.5%) and peak widths (RSD<1.5%) was observed. The columns prepared were successfully used in the second dimension of a GC×GC setup with a standard non-polar first dimension. Model experiments proved the possibility to operate both dimensions at their optimum linear velocity simultaneously. The suitability of the novel second dimension column format to perform multidimensional separations was shown for selected applications.

Highlights

► Divinylbenzene monoliths as stationary phases for new GC columns. ► Good performance for fast GC separations with a peak capacity of 12 peaks per 5s. ► New monolithic columns coupled as second dimension for GC×GC. ► Multidimensional separation of low-boiling compounds with good orthogonality. ► Possible to operate both dimensions at the optimum linear velocity simultaneously.

Analysis of linear and cyclic methylsiloxanes in sewage sludges and urban soils by concurrent solvent recondensation – large volume injection – gas chromatography–mass spectrometry

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
E.Y. Companioni-Damas, F.J. Santos, M.T. Galceran
Concurrent solvent recondensation–large volume injection (CSR–LVI) is a gas chromatography injection technique that is particularly suitable for determining volatile compounds. In the present work, we evaluated the applicability of this technique for the analysis of linear and cyclic methylsiloxanes in sewage sludges and soils after solvent extraction to prevent losses of low-molecular-weight compounds. The CSR–LVI injection method was optimised to achieve maximum sensitivity and good chromatographic peak shapes. A liner packed with deactivated glass wool and a 5m×0.32mm I.D. uncoated fused-silica precolumn was used. This made it possible to inject extract volumes of up to 30μl. Good linearity (r >0.9993) and precision (RSD <15%), with recoveries ranging from 80 to 100% and method limits of quantification from 0.03 to 0.4ngg⁻¹ wet weight (0.04–1.5ngg⁻¹ dry weight for sewage sludges and 0.01–0.5ngg⁻¹ dry weight for soils) were obtained. The developed method was applied to the analysis of linear and cyclic methylsiloxanes in sewage sludges collected from several wastewater treatment plants in Catalonia (NE Spain) and urban soils from the city of Barcelona.

Highlights

► A new method for methylsiloxane determination in sewage sludge and soils was proposed. ► The CSR–LVI technique provides high sensitivity injecting extract volumes up to 30μL. ► The method provided good precision (RSD<15%) and low LOQs (0.01–1.5ngg⁻¹ dw). ► Methylsiloxane concentrations in sludge samples ranged from 4.8 to 82,112ngg⁻¹ dw. ► Levels of cyclic methylsiloxanes in urban soils was found from 7.2 to 47ngg⁻¹ dw.

Fast separation of triterpenoids by supercritical fluid chromatography/evaporative light scattering detector

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
E. Lesellier, E. Destandau, C. Grigoras, L. Fougère, C. Elfakir
The screening of plant material, the chemical composition, the abundance and the biological activity of triterpenoids are of a major economical importance. The classical analytical methods, such as TLC, GC, and HPLC are either little resolutive, or require derivatization steps, or fail in sensitivity. The supercritical fluid chromatography/evaporative light scattering detector (SFC/ELSD) coupling provides high resolution, fast analysis and higher responses for the analysis of triterpenoids. After the initial screening of seven stationary phases to select the well suited one, analytical conditions (modifier percentage, from 10 to 3%; backpressure (from 12 to 18MPa) and temperature (from 15 to 25°C) were studied to improve the separation, and ELSD detection of a standard mixture composed of 8 triterpenoids (oleanolic acid, erythrodiol, β-amyrin, ursolic acid, uvaol, betulinic acid, betulin, lupeol). Applied to apple pomace extracts, this method allows the separation of about 15 triterpenoid compounds, in less than 20min, with isocratic conditions. Moreover, the ELSD response is dramatically higher than the one provided by UV detection, and avoids derivatization steps. An attempt to identify some compounds was done by collecting chromatographic peaks and further analyzing them with mass spectrometry. Complete identification or molecular formula could be proposed for 11 compounds. However, due to the presence of position and orientation isomers the absolute identification remains difficult, despite some retention rules deduced from the standard analysis.

Highlights

► Description of a method development in SFC. ► Improvement of the triterpenoid separation in isocratic SFC. ► Varied and complementary selectivity are obtained with different columns. ► ELSD provides higher response coefficients than UV for triterpenoids. ► Analyses of bio-active compounds present in food by-products is shown by SFC-ELSD.

Human serum albumin-coated gold nanoparticles for selective extraction of lysozyme from real-world samples prior to capillary electrophoresis

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Pei-Rong Yeh, Wei-Lung Tseng
This study describes the use of human serum albumin (HSA)-modified gold nanoparticles (HSA-AuNPs) for the selective extraction and enrichment of high-pI protein, lysozyme (Lyz) prior to analysis by capillary electrophoresis (CE) with UV detection. HSA-AuNPs are capable of extracting Lyz from a complex matrix because a HSA capping layer not only stabilizes gold nanoparticles in a high-salt environment but also exhibits strong electrostatic attraction with Lyz under neutral pH condition. Efficient separation of Lyz and other high-pI proteins has been successfully achieved by the filling of cationic polyelectrolyte, poly(diallydimethylammonium chloride) (PDDAC), to the background electrolyte. After capturing Lyz with HSA-AuNPs, PDDAC-filled CE can be directly used for the analysis of the extracted Lyz without the addition of the releasing agent into the extractor. The extraction efficiency relied on the pH of the solution and the concentration of HSA-AuNPs. Under optimal extraction conditions, the limit of detection at a signal-to-noise ratio of 3 for Lyz was down to 8nM. The combination of HSA-AuNP extraction and PDDAC-filled CE has been applied the analyses of Lyz in hen egg white, human milk, and human tear. Also, this NP-based extraction can be coupled to matrix-assisted desorption/ionization time-of-flight mass spectrometry and sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Highlights

► HSA-AuNP-based extraction can be coupled with CE, MALDI-TOF MS, and SDS-PAGE. ► This method offers simplicity, high selectivity, and high sensitivity for lysozyme. ► This method can be applied to the determination of lysozyme in real samples. ► HSA-AuNPs can selectively extract lysozyme.

Chiral speciation and determination of selenomethionine enantiomers in selenized yeast by ligand-exchange micellar electrokinetic capillary chromatography after solid phase extraction

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Jiankun Duan, Man He, Bin Hu
A new phenylalanine derivative (l-N-(2-hydroxy-propyl)-phenylalanine, l-HP-Phe) was synthesized and its chelate with Cu(II) (Cu(II)–(l-HP-Phe)2) was used as the chiral selector for the ligand-exchange (LE) chiral separation of d,l-selenomethionine (SeMet) in selenized yeast samples by micelle electrokinetic capillary chromatography (MEKC). In order to improve the sensitivity of MEKC–UV, two-step preconcentration strategy was employed, off-line solid phase extraction (SPE) and on-line large volume sample stacking (LVSS). d,l-SeMet was first retained on the Cu(II) loaded mesoporous TiO2, then eluted by 0.1mL of 5molL⁻¹ ammonia, and finally introduced for MEKC–UV analysis by LVSS injection after evaporation of NH3. With the enrichment factors of 1400 and 1378, the LODs of 0.44 and 0.60ngmL⁻¹ for l-SeMet and d-SeMet was obtained, respectively. The developed method was applied to the analysis of d,l-SeMet in a certified reference material of SELM-1 and a commercial nutrition yeast, and the results showed that most of SeMet in the SELM-1 selenized yeast was l isomer and the recovery for l and d isomers in the spiked commercial nutrition yeast was 96.3% and 103%, respectively. This method is featured with low running cost, high sensitivity and selectivity, and exhibits application potential in chiral analysis of seleno amino acids in real world samples.

Highlights

► Cu(II)–(l-HP-Phe)2 was used as the chiral selector for separation of SeMet enantiomers by CE. ► Off-line SPE combined with on-line LVSS was employed to improve the sensitivity of CE–UV. ► A novel method of SPE–LE–LVSS–CE–UV was proposed to the analysis of d,l-SeMet in yeast. ► The developed method is featured with low running cost, high sensitivity and selectivity.

Field enhanced bacterial sample stacking in isotachophoresis using wide-bore capillaries

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Farid Oukacine, Joselito P. Quirino, Delphine Destoumieux-Garzón, Hervé Cottet
The isotachophoretic analysis of different bacterial strains was studied using capillaries with different internal diameters from 50 to 250μm. Several injection modes were investigated and compared in order to improve the limit of detection of bacteria by capillary isotachophoresis. A system suitability test obtained from the separation voltage was developed to ensure reliable results. As expected, the use of wider bore capillaries improved the analytical sensitivity of the isotachophoretic method when compared to the 50μm capillary. With the optimized conditions, the isotachophoretic method presented in this work allows the quantification of Erwinia carotovora (Gram negative bacteria) with a limit of detection as low as ∼3000cellsmL⁻¹. The proposed methodology does not require any additive in the electrolyte such a fluorescent or chromophoric dye to reach these limits of detection.

Highlights

► Improvement of the limit of detection of bacteria in UV capillary isotachophoresis. ► Use of wider bore capillaries with internal diameters from 50 to 250μm. ► Development of a system suitability test to ensure reliable results. ► Limit of detection as low as 3000cellsmL⁻¹ on 200μm i.d. capillary.

Separation of Sudan dyes from chilli powder by magnetic molecularly imprinted polymer

28 November 2012, 06:39:04

Publication year: 2012
Source:Journal of Chromatography A, Volume 1268
Chunying Piao, Ligang Chen
A simple method based on magnetic molecularly imprinted polymers (MMIPs) for the separation of Sudan dyes from chilli powder samples has been developed. The MMIPs were synthesized as follows: the Fe3O4 nanoparticles were encapsulated with a SiO2 shell and functionalized with CHCH2, then the polymers were further fabricated by surface-imprinted polymerization using Sudan IV as template molecule, methacrylic acid as functional monomer, and ethylene glycol dimethacrylate as cross-linking agent. The prepared MMIPs were characterized by scanning electron microscope, Fourier transform infrared spectrometry and physical property measurement system. The isothermal absorption experiment, kinetics absorption experiment and selectivity of MMIPs were tested. The analytes were determined by high performance liquid chromatography. Under the optimal conditions, the limits of detection of the four Sudan dyes are 6.2, 1.6, 4.3 and 4.5ngg⁻¹, respectively. The precision expressed as relative standard deviation ranging from 4.8% to 9.1% was obtained. In all three fortified levels (25, 250 and 2500ngg⁻¹), recoveries of Sudan dyes were in the range of 79.9–87.8%.

Highlights

► The magnetic molecularly imprinted polymers (MMIPs) were prepared. ► Characterization and binding properties of MMIPs were studied. ► MMIPs were used for extraction of Sudan dyes in chilli powder samples. ► The satisfied results were obtained.