Check out our New Publishers' Select for Free Articles

Analytica Chimica Acta (v.558, #1-2)

Filler Ad.: ACAEES (pp. ii).

Outside front cover - Editorial Board (pp. co1).

Contents (pp. v-vii).

Calendar of forthcoming meetings (pp. n1).

Obituary by A. Townshend (pp. 1-1).

Improving the sensitivity of HPLC absorption detection by cavity ring-down spectroscopy in a liquid-only cavity by L. van der Sneppen; A. Wiskerke; F. Ariese; C. Gooijer; W. Ubachs (pp. 2-6).

A previously described liquid-only cavity flow cell is used to assess the feasibility of improving absorbance detection limits in liquid chromatography (LC) using cavity ring-down spectroscopy (CRDS). In this miniaturized cavity there is an optical path length of only 2mm between the mirrors, which at the same time form the walls of the flow cell. Typical ring-down times are 65–75ns for the eluent blank. The performance of the presented flow cell compares favorably to conventional absorbance detection: the baseline noise is determined to be 2.7×10⁻⁶A.U. using averaging over 1s. The concentration detection limits are between 15 and 20nM (injected concentrations) for compounds with a molar extinction coefficient of 1.0–1.4×10⁴M⁻¹cm⁻¹ at the laser wavelength of 532nm. The baseline noise as well as the absolute concentration detection limit is lowered by a factor of 30 as compared to measurements with a typical conventional absorbance detector. With an extra band broadening of only 15%, the flow cell is suitable for LC analysis.

Keywords: Cavity ring-down spectroscopy; CRDS; Liquid-only cavity; Absorption detection; Azo-dyes

A model for temperature effect on column efficiency in high-temperature liquid chromatography by Yu Yang (pp. 7-10).

Even though it has not been widely recognized in the chromatography community, the separation temperature should be considered as an important parameter for the optimization of chromatographic separation conditions. With the help of newly developed stationary phases that are thermally more stable, liquid chromatographic separations may be carried out at elevated temperatures for several thousands of column volumes without decomposition of the packing materials. Therefore, it is important to investigate the temperature effect on column efficiency in liquid chromatographic separations. A mathematical relationship between the plate height and temperature was established in this study. This temperature model is useful for chromatographers to understand the fundamental aspect of the temperature effect in reversed-phase liquid chromatography.

Keywords: High-temperature liquid chromatography; Model; Column efficiency; Temperature effect

Determination of chloramphenicol residues in animal feeds by liquid chromatography with photo-diode array detection by Pilar Vi�as; Nuria Balsalobre; Manuel Hern�ndez-C�rdoba (pp. 11-15).

A reversed-phase liquid chromatographic method with photo-diode array detection is presented for use in the determination of chloramphenicol. A new amide-based stationary phase prevents the interaction of the analyte with the residual silanol groups, thus avoiding the appearance of tailed peaks. Specificity was demonstrated by the retention characteristics, UV spectra and peak purity index. Linearity, precision, recovery and sensitivity were satisfactory. The procedure was applied to the analysis of residual chloramphenicol in different types of animal feed. Samples were extracted by using liquid–liquid extraction steps with organic solvents and, for the clean-up, solid-phase extraction using cartridges was applied. Detection limit in the samples using the proposed procedure was 0.7μgkg⁻¹.

Keywords: Chloramphenicol; Animal feed; Liquid chromatography; Amide stationary phase

Determination and pharmacokinetics of evodiamine in the plasma and feces of conscious rats by Ming-Hwang Shyr; Lie-Chwen Lin; Tzu-Yang Lin; Tung-Hu Tsai (pp. 16-21).

Evodiamine is one of the major quinazolinocarbolin alkaloids isolated from the fruit of dried unripened Evodia rutaecarpa Bentham. The aim of the present study is to develop an automated blood sampling method to evaluate the oral bioavailability of evodiamine in a conscious freely moving rat. The blood was collected by an automated blood sampling system after evodiamine was administered at doses of 1 and 500mg/kg through oral and intravenous administration, respectively. The fecal samples were collected by a metabolic cage over five consecutive days after the evodiamine was given orally administered to the rats. Acetonitrile was used to extract evodiamine from the feces and plasma samples. After centrifugation (8000× g, 10min), 20μl aliquot of supernatant were passed through a filter before injection into an HPLC/UV system. The analytes were separated on RP-phenyl column (150mm×4.6mm i.d., particle size 5μm) at room temperature, and eluted with acetonitrile-water (60:40 (v/v), pH 2.5 adjusted by H₃PO₄) with a flow-rate of 1.3ml/min. The UV detector was set at 227nm. The limit of detection of evodiamine was 0.01μg/ml in rat plasma and feces. The concentration–response relationship from the present method indicated linearity over a concentration range of 0.01–50μg/ml. Intra- and inter-assay precision and accuracy of evodiamine in the biological fluids fell well within the predefined limits of acceptability (<15%). Biological fluids were thereby sampled following a dose of evodiamine (500mg/kg, p.o.). The oral bioavailability was estimated to be about 0.1% in the conscious rat system.

Keywords: Evodia rutaecarpa; Bentham; Evodiamine; Herbal medicine; Liquid chromatography; Pharmacokinetics

Determination of phytic acid in wheat and wheat products by reverse phase high performance liquid chromatography by Kenan Dost; Ozge Tokul (pp. 22-27).

A sensitive method for accurate determination of phytic acid in food samples is described. The proposed procedure involves high performance liquid chromatography (HPLC) and UV–vis detection. The method was based on metal replacement reaction of phytic acid from coloured complex (iron(III)–thiocyanate), separation and monitoring any decrease in concentration of coloured complex. The retention time for the monitored iron(III)–thiocyanate peak was achieved in less then 3min in Gaussian shape. The proposed HPLC/UV–vis procedure shows good linearity over the concentration range of 10–125μgml⁻¹ with correlation coefficient value of 0.997. The procedure is reproducible and accurate, illustrating a standard deviation between 0.72 and 1.20μgml⁻¹ ( n=10, for 50μgml⁻¹) and relative standard deviation between 1.40 and 2.98% ( n=10, for 50μgml⁻¹) within and between days for reproducibility and absolute error ranging between 0.16 and 1.54% ( n=10, for 100μgml⁻¹) within and between days for accuracy, respectively. Detection limit was estimated as 0.5μgml⁻¹ which is suitable for analysis of foodstuffs and plant materials in that phytic acid usually presents within 2.5–50μgml⁻¹ range. The procedure was then applied to determination of phytic acid in wheat and wheat products. The content of the phytic acid in the samples was calculated by using the calibration curve obtained from the standard solution of phytic acid and iron(III)–thiocyanate solutions containing 100μgml⁻¹ iron(III) ion.

Keywords: Phytic acid; High performance liquid chromatography; Iron(III)–thiocyanate; Iron(III)–phytate; Wheat and wheat products

Rapid separation of soybean and cereal (wheat, corn, and rice) proteins in complex mixtures: Application to the selective determination of the soybean protein content in commercial cereal-based products by A. Castro-Rubio; M.C. Garc�a; M.L. Marina (pp. 28-34).

A perfusion reversed-phase high-performance liquid chromatography method is proposed for the rapid and simultaneous separation of soybean and cereal (wheat, rice, and corn) proteins in complex mixtures of these vegetable proteins. The method consisted of a linear binary gradient in two steps, from 5 to 10% B in 0.42min, and from 10 to 50% B in 5.71min being mobile phase A, 0.3% (v/v) acetic acid in Milli-Q water and mobile phase B, 0.3% (v/v) acetic acid in acetonitrile. A temperature of 50°C and UV detection at 254nm were used. Samples and standards were prepared in a 25:75 acetonitrile–water mixture containing 0.3% (v/v) acetic acid. The method was successfully applied to the determination of the soybean protein content in commercial cereal-based products manufactured with binary, ternary, and quaternary soybean–cereal mixtures. Moreover, the method was also valid when samples contained, in addition, other cereals such as barley, rye, and millet and other non-vegetal sources of proteins such as milk and egg proteins. Unlike the Kjeldahl method, this method enabled the selective determination of soybean proteins in these complex mixtures being possible the detection and quantitation of up to 12.5 and 42.5g/kg, respectively, of soybean proteins (related to 0.1g of sample).

Keywords: Soybean; Wheat; Corn; Rice; Proteins; Perfusion; Reversed-phase; Liquid chromatography; Quantitation of soybean proteins; Cereal-based products

The use of a thermogravimetric analyzer for the generation of primary analytical vapor standards of organophosphate pesticides by Jonathan W. Boyd; Charles K. Eckman; Nicholas A. Romero; Seshadri S. Ramkumar; Stephen B. Cox; George P. Cobb (pp. 35-41).

A thermogravimetric analyzer (TGA) was used for the generation of primary vapor standards of three organophosphate pesticides encompassing a wide range of vapor pressures. The technique combines a dynamic flow-through evaporation system with gravimetric analysis of weight loss from an analyte reservoir. Vapor reference standards may be produced in less than 1h per compound, including purging the system between compounds. Vapor concentrations are gravimetrically monitored in real-time (1Hz). Equilibration time was negligible, as the linear vaporization curves for the compounds were produced in real-time, and all had correlation coefficients ( R²) greater than 0.99. For the current study, vapors were collected by sampling bags for transport. This sensitive (parts-per-million to parts-per-billion), fast (negligible equilibration time), robust (compounds with vapor pressures spanning five orders of magnitude), low consumption (μL), and extremely general technique may be used for the generation of countless vapors in a number of concentrations and quantities.

Keywords: Thermogravimetric analyzer; Vapor generation; Primary vapor standards; Chemical warfare agent simulant; Organophosphate pesticide; Low vapor pressure

Multiresidue analysis of organochlorine and organophosphorus pesticides in muscle of chicken, pork and lamb by gas chromatography–triple quadrupole mass spectrometry by A. Garrido Frenich; J.L. Mart�nez Vidal; A.D. Cruz Sicilia; M.J. Gonz�lez Rodr�guez; P. Plaza Bola�os (pp. 42-52).

A method was optimized and validated for the simultaneous determination of residues of organochlorine (OCPs) and organophosphorus (OPPs) pesticides in meat samples from chicken, pork and lamb. The method is based in the extraction of homogenized meat mixed with sodium sulphate and ethyl acetate in polytron, although both Soxhlet and accelerated solvent extraction (ASE) were also tested. Then, a clean-up step by gel permeation chromatography (GPC) was applied, before the final determination by gas chromatography (GC) coupled to a triple quadrupole (QqQ) mass spectrometry (MS) detection system. Confirmation criteria of the pesticides were based in the 2002/657/EC European Commission Decision that establishes at least three identification points (IPs) for organic residues in live animals and animal products. The analytical process was validated in each matrix by the analysis of spiked blank samples. Performance characteristics, such as linearity, detection limit (LOD), quantitation limit (LOQ), precision and recovery were studied. Recoveries and precision values were 70.0–90.0% and 15%, respectively, for the bulk majority of pesticides. LOD<2.0 and LOQ<5.0μg/kg were obtained for all the target compounds, except for acephate. The proposed analytical methodology was applied to the analysis of the pesticides in 30 samples, 10 from chicken, 10 from pork and 10 from lamb. Only three OCPs, endosulfan α, endosulfan sulfate and dichloran were detected in three different lamb samples, while endosulfan α was detected in only one pork sample, at concentration levels lower than the LOQ values. However, pesticide residues were not found in any of the other 10 chicken samples analyzed.

Keywords: Meat; Pesticides; Gel permeation chromatography; Accelerated solvent extraction; Tandem mass spectrometry

Multiresidue analysis of pesticides in olive oil by gel permeation chromatography followed by gas chromatography–tandem mass-spectrometric determination by Andr�s Garc�a S�nchez; Natividad Ramos Martos; Evaristo Ballesteros (pp. 53-61).

A method for the multiresidue analysis of olive oil samples for 26 pesticides is proposed. Residual pesticides are extracted from oil using an n-hexane/acetonitrile mixture, extracts being cleaned-up by gel permeation chromatography (GPC) for analysis by gas chromatography–tandem mass spectrometry (GC–MS/MS). Electron ionization and chemical ionization are employed in a single analysis for the determination of pesticides. Pesticide recoveries from virgin and refined olive oil spiked with 10, 100 and 250μg/kg concentrations of the pesticides ranged from 83.8 to 110.3%. The proposed method features good sensitivity: its limits of quantification are low enough to allow pesticide residues to be determined at concentrations below the maximum residue levels legally accepted. The precision, expressed as relative standard deviation, ranges from 4.93 to 8.11%. Applicability was tested on 40 olive oil samples. Several pesticides were detected in most of the virgin olive oil samples. By contrast, refined olive samples contained few pesticides, and only endosulfan sulphate was detected in all.

Keywords: Pesticides; Olive oil; Gel permeation Chromatography; Gas chromatography; Tandem mass spectrometry

Simultaneous identification and quantitation of selected organochlorine pesticide residues in honey by full-scan gas chromatography–mass spectrometry by Yahya R. Tahboub; Mohammad F. Zaater; Thaer A. Barri (pp. 62-68).

In this work, we report a reliable method for simultaneous identification and quantitation of 11 organochlorine pesticide (OCP) residues (α-HCH, HCB, β-HCH, alachlor, heptachlor, aldrin, primiphos-ethyl (internal standard), endosulfan II, 4,4′-DDE, dieldrin, endrin and 4,4′-DDD) in honey. The method features the simultaneous identification and quantitation of targeted pesticides and the possibility of identification of any other eluting compounds. The method is based on liquid–liquid extraction (LLE) with a mixture of petroleum ether and ethyl acetate (80:20, v/v) and a cleanup with a Florosil cartridge, followed by gas chromatographic separation and a full-scan mass spectrometric detection (full-scan GC–MS). The method presents a new validation parameter, limit of identification (LOI) which is defined as the lowest analyte concentration that yields a library searchable mass spectrum. The method is linear over the range 5.0–100μgkg⁻¹. Uncertainties of slopes vary between 2.0 and 13%. Correlation coefficients vary between 0.988 for 4,4′-DDE and 0.998 for α-HCH, alachlor and aldrin. Limits of detection (LODs) vary between 0.65 and 2.5μgkg⁻¹, limits of quantitation (LOQs) vary between 2.2 and 7.5μgkg⁻¹, and LOIs vary between 1.0 and 3.0μgkg⁻¹. The method was applied by analyzing 15 local and 10 imported honey samples in Jordan.

Keywords: Organochlorine pesticides; Gas chromatography–mass spectrometry; Identification

Micro-multiphase laminar flows for the extraction and detection of carbaryl derivative by Adelina Smirnova; Kazuma Mawatari; Akihide Hibara; Mikhail A. Proskurnin; Takehiko Kitamori (pp. 69-74).

A new solvent extraction concentration method utilizing microchip technology has been developed. As an important application of this system, carbaryl determination with thermal lens microscope detection was demonstrated. Carbaryl pesticide was hydrolyzed in an alkaline medium to 1-naphthol, was coupled with diazotized trimethylaniline, and, then, was extracted to toluene as a colored azo dye. Two microchips with modified complex-shape microchannels were used for mixing, reaction, extraction, and detection. A thermal lens microscope was used for the detection of the colored product. Optimum conditions for aqueous phase and organic phase flow rates inside the microchannels were identified. The calibration line indicated good linearity for concentrations of 3.4×10⁻⁷ to 3.5×10⁻⁶M and a detection limit of 7×10⁻⁸M was obtained. This limit of detection is at least two orders less than LODs for conventional spectrophotometric methods. The results with the present integrated system suggested there was a good potential for implementing an on-site carbaryl analysis system.

Keywords: Microchip; Thermal lens microscopy; Liquid–liquid interface; Solvent extraction; Carbaryl

Quantitative extraction using flowing nano-liter droplet in microfluidic system by Momoko Kumemura; Takashi Korenaga (pp. 75-79).

Quickly extraction system using dispersed droplet in T-shaped microchannel has been constructed and investigated for the determination of aluminum in water. The droplet was generated in T-shaped microchannel with 600μm wide and 200μm deep in continuous phase and 70μm wide and 20μm deep in dispersed phase by flowing two immiscible solutions, buffer solution containing aluminum and tributyl phosphate as dispersed phase. By varying the flow rate of two solutions, the droplet volume could be controlled in the range from 0.6 to 32nL. Using this droplet generation in microchannel, aluminum in continuous phase was extracted with 2,2-dihydroxyazobenzene as a metal chelate from buffer solution to tributyl phosphate for 1s, which was 90 times shorter than that of a conventional extraction method using a separatory funnel. Estimated overall mass transfer coefficient was to be 57×10⁻⁴mms⁻¹ with 0.6nL droplet. And quantitative extraction was performed in this extraction system by detecting droplets before it reached to extraction equilibrium. Furthermore, this extraction system was applied to environmental analysis for evaluation of its validity, and the results were in agreement with the conventional extraction method ( r=0.92).

Keywords: Microchip analysis; Droplet; Extraction; Aluminum ion; Laser-induced fluorescence; Microscopy

Amino-substituted β-cyclodextrin copper(II) complexes for the electrophoretic enantioseparation of dansyl amino acids: Role of dual chelate–inclusion interaction and mechanism by Bidong Wu; Qingqing Wang; Lei Guo; Rui Shen; Jianwei Xie; Liuhong Yun; Bohua Zhong (pp. 80-85).

The four amino-substituted β-cyclodextrins were synthesized and used as the chiral ligands to form the copper(II) complexes, respectively. CDen copper(II) complex was applied as the model selector to optimize the electrophoresis conditions and all the selected chiral dansyl amino acids were baseline separated under the proposed method, the optimum experimental conditions were 10mmol/L CDen, 10mmol/L CuSO₄·5H₂O, 5.0mg/mL PEG20000 and 1.5% (v/v) tertbutyl alcohol, pH 4.2. By comparing the enantioselectivity of the copper(II) copmplexes of four amino-substituted β-CDs, the cooperation between the inclusion and chelate interaction was demonstrated to be the key factor to obtain satisfactory chiral discrimination ability. Fluorescence experiments were carried out to investigate microenvironment of the chiral recognition process, which indicated that the order of penetration depth of dansyl group into the host cavity is CD>CDen copper(II) complex>CDdien copper(II)complex, and the molecular bulk of derivatization reagents has great effect on the chiral separation.

Keywords: Chiral separation; Amino-substituted β-cyclodextrins; Amino acids; Capillary electrophoresis; Fluorescence

Prediction of retention in micellar electrokinetic chromatography based on molecular structural descriptors by using the heuristic method by Huanxiang Liu; Xiaojun Yao; Mancang Liu; Zhide Hu; Botao Fan (pp. 86-93).

Based on calculated molecular descriptors from the solutes’ structure alone, the micelle–water partition coefficients of 103 solutes in micellar electrokinetic chromatography (MEKC) were predicted using the heuristic method (HM). At the same time, in order to show the influence of different molecular descriptors on the micelle–water partition of solute and to well understand the retention mechanism in MEKC, HM was used to build several multivariable linear models using different numbers of molecular descriptors. The best 6-parameter model gave the following results: the square of correlation coefficient R² was 0.958 and the mean relative error was 3.98%, which proved that the predictive values were in good agreement with the experimental results. From the built model, it can be concluded that the hydrophobic, H-bond, polar interactions of solutes with the micellar and aqueous phases are the main factors that determine their partitioning behavior. In addition, this paper provided a simple, fast and effective method for predicting the retention of the solutes in MEKC from their structures and gave some insight into structural features related to the retention of the solutes.

Keywords: Heuristic method; Quantitative structure–retention relationship; MEKC; Micelle–water partition coefficient

Analyte species and concentration identification using differentially functionalized microcantilever arrays and artificial neural networks by Larry R. Senesac; Pampa Dutta; Panos G. Datskos; Michael J. Sepaniak (pp. 94-101).

In the present work, we have performed analyte species and concentration identification using an array of ten differentially functionalized microcantilevers coupled with a back-propagation artificial neural network pattern recognition algorithm. The array consists of ten nanostructured silicon microcantilevers functionalized by polymeric and gas chromatography phases and macrocyclic receptors as spatially dense, differentially responding sensing layers for identification and quantitation of individual analyte(s) and their binary mixtures. The array response (i.e. cantilever bending) to analyte vapor was measured by an optical readout scheme and the responses were recorded for a selection of individual analytes as well as several binary mixtures. An artificial neural network (ANN) was designed and trained to recognize not only the individual analytes and binary mixtures, but also to determine the concentration of individual components in a mixture. To the best of our knowledge, ANNs have not been applied to microcantilever array responses previously to determine concentrations of individual analytes. The trained ANN correctly identified the eleven test analyte(s) as individual components, most with probabilities greater than 97%, whereas it did not misidentify an unknown (untrained) analyte. Demonstrated unique aspects of this work include an ability to measure binary mixtures and provide both qualitative (identification) and quantitative (concentration) information with array-ANN-based sensor methodologies.

Keywords: Microcantilever array; Pattern recognition; Artificial neural networks; Polymeric and gas chromatography phases

Microsphere sedimentation arrays for multiplexed bioanalytics by Christoph Moser; Torsten Mayr; Ingo Klimant (pp. 102-109).

A new measurement platform to analyze multiple assays in parallel in a single well of a standard microplate is presented. The approach is based on optically addressable encoded microbeads as carriers for a series of bioassays, a fluorescence microscope equipped with a LED as excitation source, a fast-gateable CCD-camera and automated image analysis. Bead arrays are suspended in the analyte solution and targets are bound to receptors immobilized at the bead surface. Gravitational or magnetical sedimentation of the beads to the transparent bottom of the microplate leads to in situ formation of randomly ordered arrays. Beads are encoded by three features: size, luminescence intensity and luminescence decay time. Luminescence lifetime imaging in the microsecond range is introduced as a new technique for bead identification. Twenty-seven distinguishable bead classes were produced and characterized. The coefficients of variation were 5.4% for size, 9% intensity and 1.3% for decay time. Based on these results, the number of potential codes is calculated to be about 140. Multiplexed DNA assays at detection limits of 2nM were carried out to demonstrate the feasibility of the concept presented here.

Keywords: Abbreviations; CV; coefficient of variation; Ru(dpp); ₃; Cl; ₂; tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) chloride; PS; polystyrene; MF; melamine–formaldehydeMultiplexed analysis; Suspension array; Sedimentation array; Magnetic microbead; Luminescence, decay imaging

Scanning electrochemical microscopy with enzyme immunoassay of the cancer-related antigen CA15-3 by Xiaoli Zhang; Xuewei Peng; Wenrui Jin (pp. 110-114).

Scanning electrochemical microscopy (SECM) with enzyme immunoassay was applied to detect the cancer related antigen CA15-3 (Ag). In this method, CA15-3 was concentrated and immobilized on a plane substrate via a sandwich method employing two corresponding antibody (Ab captured on a streptavidin-coated substrate and Ab^* labeled with horseradish peroxidase (HRP)). In the presence of hydroquinone (H₂Q) and H₂O₂, HRP on the complex of CA15-3 with Ab and Ab^*, Ab–Ag–Ab^*, converted H₂Q to the electroactive product benzoquinone (BQ) through the HRP-catalyzed reaction. The reduction current of BQ generated by the HRP-catalyzed reaction corresponding to the amount of CA15-3 was monitored and imaged by SECM. With a view of improving the sensitivity of SECM-enzyme immunoassay to meet our objective, Ab–Ag–Ab^* was concentrated on the substrate via a microcell. The detection limit of this method was 2.5U/mL for CA15-3.

Keywords: Enzyme immunoassay; Scanning electrochemical microscopy; Cancer related antigen; CA15-3

The use of time-of-flight static secondary ion mass spectrometry imaging for the molecular characterization of single aerosol surfaces by Rita Van Ham; Annemie Adriaens; Luc Van Vaeck; Freddy Adams (pp. 115-124).

The imaging feasibility of time-of-flight static secondary ion mass spectrometry (TOF S-SIMS) has been investigated for the identification of the molecular composition of inorganic constituents at the surface of single aerosol particles. Selected test cases involved the study of single ambient aerosol particles (aerodynamic diameter 2–4μm) collected by cascade impaction and the characterization of laboratory made CaCO₃ particles exposed to HNO₃ and H₂SO₄. A methodological optimization of the experiments helped in identifying a proper collection substrate (silicon wafer), the use of a low particle loading and the application of sputter pre-cleaning as essential aspects to record high quality secondary ion images of molecule specific adduct ions (i.e. one or more analyte molecules attached to a stable ion). Correlation of the features in the ion images at different m/ z and the knowledge about the systematic trends in the formation of structural ions from inorganic salts allowed the identification of the molecular composition of the constituents in the studied particles.

Keywords: Aerosols; Speciation; Imaging; Surface analysis; TOF S-SIMS

Sensitivity and specificity of PLS-class modelling for five sensory characteristics of dry-cured ham using visible and near infrared spectroscopy by M. Cruz Ortiz; Luis Sarabia; Raquel Garc�a-Rey; M. Dolores Luque de Castro (pp. 125-131).

The two objectives of this work were to evaluate near infrared reflectance spectroscopy (NIR) as a tool for on-line classification of dry-cured ham samples according to their sensory characteristics and propose a method for obtaining a set of qualified class models that enables accurate decisions to be taken. With these aims, 117 dry-cured ham samples were classified by expert judges as compliant or non-compliant concerning sensory variables as pastiness, colour, crusting, marbling and ring colour. These samples were also scanned using a remote reflectance fiber optic probe.Each class model built for each sensory variable is evaluated for its sensitivity and specificity, parameters related with the probability of false non-compliance ( α) and false compliance ( β) of “H₀: the sample is compliant�? hypothesis test.With the five sets of PLS-class modelling the five risk curves, graphs β versus α, are estimated. It is therefore possible to choose the risks of false compliance and false non-compliance for each sensorial variable according to the needs of the decision-maker.

Keywords: NIR; Dry-cured ham; Sensorial analysis; Partial least squares class model; Risk curve

Near infrared spectroscopy (NIRS) reflectance technology for determination of tocopherols in animal feeds by Inmaculada Gonz�lez-Mart�n; Jos� Miguel Gonz�lez-Cabrera Myriam Bustamante-Rangel; M. Milagros Delgado-Zamarre�o (pp. 132-136).

The Vitamin E (α-, (β+γ)- and δ-tocopherol) contents present in feeds of different textures used in animal feed were analysed using near infrared spectroscopy (NIRS) technology together with a remote reflectance fibre-optic probe. The range of Vitamin E was 0.06 and 1.87mg/100g. The regression method employed was modified partial least squares (MPLS). The equations developed using the fiber-optic probe for 44 samples to determine the content of Vitamin E in feeds, in prediction, had multiple correlation coefficients (RSQ) and corrected standard errors (SEP (C)): 0.792, 0.223mg/100g for α-tocopherol, of 0.766 and 0.022mg/100g for (β+γ)-tocopherol, and of 0.789 and 0.112mg/100g for δ-tocopherol. The predicted values of Vitamin E in feeds using NIRS technology applying the fibre-optic probe directly on the sample with neither previous treatment nor manipulation are comparable to the values obtained using the chemical method that includes alkaline hydrolysis and extraction with hexane of the vitamin from the unsaponifiable fraction before chromatographic determination.

Keywords: Vitamin E; Tocopherols; Near infrared spectroscopy; Fibre-optic probe; Animal feed

Trilinear evolving factor analysis for the resolution of three-way multi-component chromatograms by Zhi-Guo Wang; Jian-Hui Jiang; Yu-Jie Ding; Hai-Long Wu; Ru-Qin Yu (pp. 137-143).

In the resolution of overlapping chromatographic peaks, reliable information about the concentration windows of all chemical components is crucial for the success of many multivariate resolution methods. In this paper, taking the advantage of trilinearity that is intrinsic in many three-way data arrays, the trilinear evolving factor analysis (TEFA) is derived to establish a trilinear rank map for three-way multi-component chromatograms. With the information of local rank obtained from the trilinear rank map, selective region of each component can be determined. This provides the possibility to resolve the profiles of a single component one by one. It is shown that combining the local eluting information and the coupled vector resolution, a fast and reliable non-iterative resolution of the trilinear data array can be obtained. Simulated and real experimental results have demonstrated that the proposed method possesses the properties of easy implementation and excellent performance for the resolution of three-way multi-component chromatograms.

Keywords: Evolving factor analysis; Trilinearity; COVER; Trilinear evolving factor analysis

Discrimination of wines based on 2D NMR spectra using learning vector quantization neural networks and partial least squares discriminant analysis by Saeed Masoum; Delphine Jouan-Rimbaud Bouveresse; Joseph Vercauteren; Mehdi Jalali-Heravi; Douglas Neil Rutledge (pp. 144-149).

The learning vector quantization (LVQ) neural network is a useful tool for pattern recognition. Based on the network weights obtained from the training set, prediction can be made for the unknown objects. In this paper, discrimination of wines based on 2D NMR spectra is performed using LVQ neural networks with orthogonal signal correction (OSC). OSC has been proposed as a data preprocessing method that removes fromX information not correlated toY. Moreover, the partial least squares discriminant analysis (PLS-DA) method has also been used to treat the same data set. It has been found that the OSC–LVQ neural networks method gives slightly better prediction results than OSC–PLS-DA

Keywords: Learning vector quantization (LVQ) neural networks; Partial least squares (PLS) discriminant analysis; Orthogonal signal correction (OSC); Principal component transform; 2D NMR spectra

In situ electrochemical and surface plasmon resonance (SPR) studies of aniline-carboxylated aniline copolymers by Yanju Wang; Wolfgang Knoll (pp. 150-157).

Self-doped conducting polyanilines (PAn) were fabricated by electrochemical copolymerization of aniline and carboxylated anilines in acidic aqueous solution using cyclic voltammetry. The comparative studies of carboxyl substituted and unsubstituted polyanilines show that only the copolymers from aniline (An) and 2-anthranilic acid (AA) with appropriate monomer fractions retain a high electroactivity and stability on electrodes in neutral aqueous solution. The polymerization process, the redox properties and the stability of the copolymers in comparison with those of polymers on gold electrodes were thoroughly investigated by in situ electrochemistry and surface plasmon resonance spectroscopy (SPR). The “self-inhibiting effect�? and the “autocatalytic effect�? were observed in the substituted and the unsubstituted polyanilines separately during the polymerization processes monitored by SPR. The combination of electrochemical and SPR techniques provides the direct information about the changes of dielectric properties and film thickness of the polymers in their redox processes. Comparing with those of PAn and copolymers, the dielectric constants of the substituted polyaniline play a minor role in the SPR reflectivity when it changes between different redox states. The comparable electroactivity of these copolymers obtained from aniline and its substituted analogues in acidic environments indicates the presence of a similar conjugated structure of the copolymer and the polyaniline, which is further confirmed by total internal reflection FTIR (TIR-IR).

Keywords: Carboxylated copolyaniline; Electropolymerization; Surface plasmon resonance; Electroactive polymer

The development of an electrochemical sensor for the determination of cyanide in physiological solutions by A.E. Lindsay; Danny O’Hare (pp. 158-163).

Hydrogen cyanide gas produced during fires can cause poisoning from smoke inhalation. Blood cyanide concentrations in healthy subjects are sub-micromolar. Toxic or fatal blood concentrations are generally considered to be greater than 40μmoldm⁻³ but concentrations in survivors can exceed 200μmoldm⁻³, while values exceeding 400μmoldm⁻³ have been recorded from fatalities.Cyanide in blood is either free in plasma or bound to ferric haemoglobin. Current analytical techniques require sample pre-treatment, generally with extraction of the cyanide from the sample. An amperometric test was developed which could determine free cyanide at physiological pH in a solution of albumin and other blood constituents without sample pre-treatment, with a calibration range exceeding 400μmoldm⁻³ and a limit of detection (LOD; using three standard deviations) of 4μmoldm⁻³ which is lower than would be treated clinically.

Keywords: Electroanalysis; Cyanide; Gold; Physiological; Sensor; Amperometric

Glutathione amperometric detection based on a thiol–disulfide exchange reaction by Francesco Ricci; Fabiana Arduini; Catalin S. Tuta; Ugo Sozzo; Danila Moscone; Aziz Amine; Giuseppe Palleschi (pp. 164-170).

A method based on a thiol–disulfide exchange reaction is proposed for glutathione detection. The method utilises a reaction between glutathione and an excess of the disulfide cystamine which produces an equimolar concentration of the thiol cysteamine. This latter is then detected at Prussian Blue modified screen printed electrodes at an applied potential of 200mV versus Ag/AgCl. First the cysteamine analytical parameters were optimised, resulting in a detection limit of 10⁻⁶moll⁻¹ and a linear range up to 10⁻⁴moll⁻¹. Reproducibility (R.S.D.=7%, n=6) and stability (more than 30 measurements with the same electrode) were satisfactory. Then the reaction between the disulfide cystamine and the thiol glutathione was optimised and a pH of 7.4 with a concentration of cystamine of 10⁻²moll⁻¹ was chosen as the best conditions in terms of reaction rate and sensor sensitivity. Glutathione was then measured under the optimised conditions giving a detection limit of 2×10⁻⁶moll⁻¹ and a linear range up to 5×10⁻⁴moll⁻¹. Blood samples were also tested in order to determine the recovery of the method. Recoveries between 92 and 103% were observed for glutathione concentrations in blood ranging from 0.5 to 3×10⁻³moll⁻¹.

Keywords: Glutathione; Screen printed electrode; Amperometric; thiol–disulfide exchange reaction

Electrochemical monitoring of phytochelatin accumulation in Nicotiana tabacum cells exposed to sub-cytotoxic and cytotoxic levels of cadmium by Miroslav Fojta; Miloslava Fojtová; Luděk Havran; Hana Pivoňková; Vlastimil Dor�?ák; Ivana Šestáková (pp. 171-178).

Cadmium belongs to the most dangerous environmental pollutants among the toxic heavy metals seriously affecting vital functions in both animal and plant cells. It has been previously shown that cadmium ions at 50–100μM concentrations caused tobacco BY-2 (TBY-2) cells to enter apoptosis within several days of exposure. Phytochelatins (PCs), the “plant metallothioneins�?, are cysteine-rich peptides involved in detoxification of heavy metals in plants. The PCs are synthesized in response to the heavy metal exposure. In this paper, we utilized electrochemical analysis to monitor accumulation of PCs in the TBY-2 cells exposed to cadmium ions. Measurements of a characteristic PC signal at mercury electrode in the presence of cobalt ions made it possible to detect changes in the cellular PC levels during the time of cultivation, starting from 30min after exposure. Upon TBY-2 cultivation in the presence of cytotoxic cadmium concentrations, the PC levels remarkably increased during the pre-apoptotic phase and reached a limiting value at cultivation times coinciding with apoptosis trigger. The PC level observed for a sub-cytotoxic cadmium concentration (10μM) was about three-times lower than that observed for the 50 or 100μM cadmium ions after 5 days of exposure. We show that using a simple electrochemical analysis, synthesis of PCs in plant cells can be easily followed in parallel with other tests of the cellular response to the toxic heavy metal stress.

Keywords: Cadmium; Phytochelatins; Electrochemical analysis; Brdicka reaction; Plant cell; Apoptosis

Direct electrochemistry and electrocatalysis of heme-proteins in regenerated silk fibroin film by Yunhua Wu; Qiuchan Shen; Shengshui Hu (pp. 179-186).

A biocompatible silk fibroin (SF) film provided a feasible microenvironment for heme-proteins to direct electron transfer on graphite electrodes (GE). Myoglobin (Mb), hemoglobin (Hb), horseradish peroxidase (HRP), and catalase (Cat) in corporated in SF films exhibited a pair of well-defined, nearly reversible cyclic voltammetric peaks, corresponding to the reaction of hemeFe (III)+e→hemeFe (II). The formal potential ( E⁰), the apparent coverage ( Γ) and the electron transfer rate constant ( k_s) of four proteins in SF films were evaluated by analyzing the cyclic voltammograms (CVs) of heme-proteins. The formal potential was pH dependent, suggesting that proton ion was involved in the reaction. Ultraviolet visible (UV–vis) spectra and reflectance absorbance infrared (RAIR) spectra indicated that heme-proteins in SF films were not grossly denatured. The structure of heme-proteins–SF films was investigated using scanning electron microscopy (SEM) and RAIR. It indicated that there existed intermolecular interaction between heme-proteins and SF and this governed their different morphology in SF films. Hydrogen peroxide and nitric oxide were catalytically reduced by the heme-proteins in SF films, showing the potential applicability of the heme-proteins–SF films as the new type of biosensors based on the protein film voltammetry.

Keywords: Myoglobin; Hemoglobin; Horseradish peroxidase; Catalase; Silk fibroin; Direct electrochemistry; Electrocatalysis

Monitoring the effect of glucosamine and glyceraldehyde glycation on the secondary structure of human serum albumin and immunoglobulin G: An analysis based on circular dichroism, thermal melting profiles and UV–fluorescence spectroscopy by Udayan Dutta; Menashi A. Cohenford; Joel A. Dain (pp. 187-194).

Glucosamine and glyceraldehyde can nonenzymatically interact with proteins to form advanced glycation endproducts (AGEs). The objective of this investigation was to determine the effects of nonenzymatic glycation by glucosamine and glyceraldehyde on the secondary structure of human serum albumin (HSA) and human IgG and to also demonstrate the in vitro formation of AGEs by these two sugars under different conditions. The formation of AGEs was monitored by capillary electrophoresis, UV and fluorescence spectroscopy. The changes in the secondary structure of HSA and IgG were determined by circular dichroism (CD) and thermal melting (Tm) profiles of the native and glycated proteins. CD and Tm studies revealed that at 40mM sugar concentration, glucosamine had a stabilizing effect on HSA and destabilized IgG whereas glyceraldehyde destabilized both the α-helical and β-pleated conformations of HSA and IgG, respectively. HSA and IgG structures were also negatively impacted with 40mM glucose.

Keywords: Advanced glycation endproducts (AGEs); Human serum albumin; Immunoglobulin G; Glucosamine; Glyceraldehyde

Speciation analysis of volatile and non-volatile vanadium compounds in Brazilian crude oils using high-resolution continuum source graphite furnace atomic absorption spectrometry by F�bio G. Lepri; Bernhard Welz; Daniel L.G. Borges; Alessandra F. Silva; Maria Goreti R. Vale; Uwe Heitmann (pp. 195-200).

A method is proposed that makes possible determining total and “thermally stable�? vanadium in crude oil without prior separation, and to calculate “volatile�? vanadium by difference. The volatile fraction is believed to be largely vanadyl porphyrine complexes. The method is based on the unsurpassed background correction capability of high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS), which allows pyrolysis temperatures as low as 300°C to be used. The samples were prepared as oil-in-water emulsions, and aqueous standards emulsified in the same way were used for calibration. Total vanadium has been determined using a pyrolysis temperature of 400°C, and “thermally stable�? vanadium using a pyrolysis temperature of 800°C. The content of total vanadium in 12 Brazilian crude oil samples was found to be between less than 0.04 and about 30mgkg⁻¹. The volatile fraction was between 5 and 51% of the total content, and there was no correlation between the total and the volatile vanadium content. The limits of detection and quantification were 0.04 and 0.12mgkg⁻¹ of V in crude oil, respectively, based on a mass of 2g of oil in 10mL of emulsion. The precision was better than 4% at the 3mgkg⁻¹ level and better than 1.5% at the 30mgkg⁻¹ level of V in crude oil.

Keywords: Vanadium in crude oil; Graphite furnace atomic absorption spectrometry; High-resolution continuum source atomic absorption spectrometry; Volatile vanadyl porphyrins; Palladium modifier

Evaluation of samplers and filter materials for the establishment of trace metal concentration profiles in peat bog porewaters using inductively coupled plasma-mass spectrometry by Nicole Rausch; Liisa Ukonmaanaho; Tiina M. Nieminen; Michael Krachler; Ga�l Le Roux; William Shotyk (pp. 201-210).

Two different types of sampler were used for the collection of humic-rich porewaters from ombrotrophic bogs at background and contaminated sites: a syringe-type sampler, which required manual filtration and dialysis chambers (peepers) where samples were filtered in situ. Concentrations of 10 trace elements Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, V and Zn have been determined in the collected porewater samples using inductively coupled plasma-sector-field-mass spectrometry. The accuracy of the analytical procedures was evaluated by the regular analyses of the two certified riverine water reference materials SLRS-2 and SLRS-4, respectively. For the syringe-type sampler, four different 0.45μm syringe filters were tested. Low blank values together with sufficiently low filtration artefacts were obtained using unwashed GD/XP filters (Whatman). When pre-cleaned filters were used, Cu and Mo showed strong filtration artefacts. Mean metal concentrations of filtrates differed by up to five times, depending on the filter type used. Overall blank values of the sampling devices were as follows (ngl⁻¹): Cd 1, Co 9, Cr 50, Cu 70, Mn 200, Mo 20, Ni 100, Pb 4, V 10, Zn 1000. The contribution of atmospheric dust during the on-site filtration might have enhanced overall blank levels of Cr, Cu and Zn when protective covers were not used during sample collection/on-site filtration. Metal concentrations at background sites were at ngl⁻¹ levels except for Zn and Mn (low μgl⁻¹). With the exception of Co and Mn, dialysis chambers were not suitable for sampling porewaters at these concentration levels.

Keywords: Trace metals; ICP-MS; Sample collection; Porewater

A new method for the investigation of mercury redox chemistry in natural waters utilizing deflatable Teflon^� bags and additions of isotopically labeled mercury by Lindsay M. Whalin; Robert P. Mason (pp. 211-221).

The toxicity and behavior of mercury (Hg) varies greatly between its chemical species, yet the mechanisms which control the redox chemistry of Hg in natural waters are still poorly understood. Previous studies have identified these processes and compared the Hg redox chemistry between water types but have been hampered by errors associated primarily with the type of reaction vessels utilized, and the inability of the methods to simultaneously measure oxidation and reduction. Presented here are the results of experiments which demonstrate the validity of a new method that addresses both these issues through the design and use of a new reaction vessel, a 5L PFA Teflon^® incubation bag, and by the addition of isotopically labeled inorganic Hg species (both Hg^II and Hg⁰). The method development showed that mm thick FEP Teflon^® is permeable to Hg⁰, and therefore unsuitable. Application of this method showed that both oxidation and reduction occurred simultaneously in natural waters exposed to ambient sunlight and that the rate of these transformations were of similar order (10⁻³ to 10⁻⁴s⁻¹). Given such reaction rates, the characteristic time to equilibrium is rapid, on the order of hours. The method is applicable for tracer studies, and the method was able to quantify rate constants of greater than 10⁻⁵s⁻¹. Overall, this study suggests that the rates of reaction are faster than previously predicted primarily because previous studies did not account for the fact that both reactions are occurring simultaneously in natural waters.

Keywords: Oxidation; Reduction; Stable isotopes; Incubation; Kinetics

Diffusion coefficients of metals and metal complexes in hydrogels used in diffusive gradients in thin films by Shaun Scally; William Davison; Hao Zhang (pp. 222-229).

Diffusion coefficients of metal ions and metal–ligand complexes in hydrogels were measured at ionic strengths of 0.1–100mmolL⁻¹ using a diffusion cell. The three different types of hydrogel were all based on polyacrylamide and have been commonly used in the technique of diffusive gradients in thin films (DGT), where accurate diffusion coefficients are essential for the assessment of the concentrations of labile metal in solution. There was little difference in the diffusion coefficients of either Cu and Cd measured in gels with thicknesses of 0.4, 0.8 and 1.6mm, showing that any diffusion boundary layer in solution was negligibly small. The diffusion coefficients of Pb, Ni, Cu and Cd in simple inorganic solutions was independent of ionic strength (1–100mmolL⁻¹), except at very low ionic strengths (0.1mmolL⁻¹) where the value of D was 50% lower. This observation is consistent with the gel having a positive charge that creates a Donnan partitioning of cations at the gel surface. Diffusion coefficient of Pb complexes decreased with increasing size of the ligand, in the order of diglycolic acid (DGA), nitrilotriacetic acid (NTA), fulvic acid and humic acid. In freshwaters the contribution of fulvic acid species to measured DGT mass should be considered. No significant difference was found between the rate of diffusion of Cu and Cd through the mostly commonly used gel and the filter membrane at the face of the DGT device. Diffusion coefficients obtained using a gel with small pore size (restricted gel) plus filter membrane were higher than those obtained using the restricted gel alone. It may be necessary to modify the standard DGT equation for restricted gel deployments, to take into account the difference in diffusion between the gel and the filter membrane.

Keywords: DGT; Diffusion coefficient; Trace metals; Complexes; Hydrogel

Principles and applications of colorimetric solid-phase extraction with negligible depletion by Neil C. Dias; Marc D. Porter; James S. Fritz (pp. 230-236).

Colorimetric solid-phase extraction (C-SPE) is an integrated technique in which an analyte is selectively concentrated onto a disk and then quantitated by diffuse reflectance spectroscopy. This paper describes the results of an investigation that applies the concept of negligible depletion (ND) to C-SPE, representing the first application of ND concepts to solid-phase extractions. The approach relies on passing the minimal volume of sample through the disk required to reach an equilibrium in which the concentration of analyte in the sample entering and exiting the disk are equal. At this point, the amount of analyte extracted by the disk is proportional to the sample concentration but is independent of the sample volume passed through the disk. With this new method, called C-SPE/ND, the precise measurement of sample volume is no longer necessary. The work herein details the general principles of this new methodology, and validates its basic tenets in an investigation of the extraction of the organic dye methyl violet. The analytical capabilities of C-SPE/ND are then demonstrated by its application to measurements of iodine. Iodine is a biocide increasingly used as a simple and effective disinfectant for water in locations where municipal water treatment systems are potentially compromised. Thus, the ability to operate C-SPE in an ND mode notably enhances the broad-based utility of this methodology as a reliable and an easy-to-use analysis tool for water quality assessments. Since iodine is also the biocide used on NASAs Space Shuttle, C-SPE/ND has the potential to overcome problems associated with the removal of air bubbles entrapped in a water sample in the microgravity environment encountered in space exploration. Extensions of C-SPE/ND to facile determinations of other water quality parameters with respect to both earth- and space-based needs are briefly discussed.

Keywords: C-SPE; Negligible depletion; Spectrophotometry; Solid-phase extraction; Water analysis; Iodine

A rapid Chelex column method for the determination of metal speciation in natural waters by K.C. Bowles; S.C. Apte; G.E. Batley; L.T. Hales; N.J. Rogers (pp. 237-245).

A simple, rapid Chelex resin column method has been developed for the determination of metal speciation in natural water samples. A water sample (pH 6–8.2) was pumped through a small plug of the Ca-form of Chelex 100 at a flow rate of 48±4mL/min. The flow regime was optimised to give the shortest possible contact time (0.25s) but at the same time ensured quantitative uptake of inorganic metal standards onto the resin. Labile metal was calculated as the difference between influent and effluent metal concentrations, measured by some form of atomic spectrometry. In tests with six metal-spiked natural freshwater samples (10μg/L added metal, pH 7.0–8.2), the labile fraction measured ranged from 87 to 98%, 32 to 64%, 12 to 78%, 38 to 91% and 63 to 89% for cadmium, copper, lead, nickel and zinc, respectively. Application of the method to copper-contaminated waters showed that the results provided a conservative estimate of the fraction inhibiting growth of a copper-sensitive bacterium, thus proving to be a useful measure of bioavailability. Tests on a range of model metal complexes showed that the measured labile metal fraction was inversely proportional to log K, and controlled by the kinetics of metal complex dissociation. Iron-containing colloids, present in natural freshwaters were not retained by the column. The method therefore discriminates trace metal species on the basis of both size and kinetics.

Keywords: Chelex; Copper; Lead; Nickel; Zinc; Cadmium; Lability; Speciation; Water quality

Synthesis of a chitosan-based chelating resin and its application to the selective concentration and ultratrace determination of silver in environmental water samples by Rosi Ketrin Katarina; Toshio Takayanagi; Mitsuko Oshima; Shoji Motomizu (pp. 246-253).

A novel chelating resin using chitosan as a base material, ethylenediamine-type chitosan, has been synthesized for the first time in the present study, and applied to the collection/concentration of ultratrace amounts of silver in environmental water samples. In the present study, ultratrace amounts of silver collected on the resin were eluted and determined by ICP-MS. The resin packed in a 1mL mini column could adsorb silver selectively and quantitatively at a flow rate of 2mLmin⁻¹ in the wide pH range from 1 to 8, and silver adsorbed on the resin could be easily recovered by passing 1M nitric acid as an eluent into the column. High adsorption capacity for silver at pH 5, 0.37mmolmL⁻¹ of the resin, was achieved, and t_1/2 of the adsorption is less than 5min. The effect of chloride on the collection of silver was examined by varying chloride concentrations from 10⁻⁴ to 0.75M; the results showed that the present resin can be used for the collection/concentration of ultratrace amounts of silver in natural waters, as well as seawater. To ensure the accuracy and the precision of the method, CASS-4 near shore seawater reference material from the NRCC has been analyzed. This is not a certified SRM for silver, but has been used for comparative silver analysis by several groups, who report very similar results to those that are reported here. The developed method using ethylenediamine-type chitosan resin gives 0.7pgmL⁻¹ of the detection limit when 50-fold enrichment was used. The proposed method was successfully applied to the determination of silver in tap, river, and seawater samples.

Keywords: Chelating resin; Chitosan; Determination of silver; Environmental water samples; ICP-MS

Selective recoveries of Fe(III) and Cr(III) from a tannery filtrate using Cyanex 923 by Akash Deep; Paulo F.M. Correia; Jorge M.R. Carvalho (pp. 254-260).

The separation of Fe(III) and Cr(III) has been proposed by liquid–liquid extraction with 0.50M Cyanex 923. Fe(III) was selectively extracted from the mixed H₂SO₄ and NaCl medium leaving pure Cr(III) in the raffinate. The developed method has been used to separate and recover Fe(III) and Cr(III) from a tannery filtrate. The modeling experiments, simulating the concentration of Fe(III) and H₂SO₄ in the original tannery filtrate, have suggested the presence of the metal ion predominantly in the form of FeHSO₄²⁺. The addition of Cl⁻ ions in the aqueous phase resulted into the development of FeCl₃, which was extractable in Cyanex 923 by solvation with two extractant molecules. The kinetics of the extraction was reasonably fast. The stripping of Fe(III) has been carried out by 0.25M H₂SO₄. The extractant solution maintained its capacity even after repeated extraction and stripping cycles.

Keywords: Liquid–liquid extraction; Recovery; Fe(III); Cr(III); Tannery filtrate; Cyanex 923

Analysis of 35 priority semivolatile compounds in water by stir bar sorptive extraction–thermal desorption–gas chromatography–mass spectrometry by V.M. Le�n; J. Llorca-P�rcel; B. �lvarez; M.A. Cobollo; S. Mu�oz; I. Valor (pp. 261-266).

A multiresidue method for the determination of 35 organic micropollutants, pesticides, and polycyclic aromatic hydrocarbons (PAHs) in water using stir bar sorptive extraction (SBSE) and thermal desorption coupled to capillary gas chromatography–mass spectrometry (SBSE–TD–GC–MS) has been validated. Method sensitivity, linearity, repeatability and reproducibility, accuracy, matrix effects, and overall uncertainties have been studied for method validation according to the international norm ISO/IEC 17025:1999. The quantification limits ranged from 0.1 to 36ng/L working in the MS full scan mode. Correlation coefficients of the calibration curves from 20 to 600ng/L were higher than 0.990 for all the compounds. To validate matrix effects for tap water, ground water and surface water, repeatability, reproducibility, accuracy and overall uncertainty were calculated for the three matrices at 50 and 500ng/L levels. The accuracy of the method was also evaluated by participating in a proficiency interlaboratory test with real samples.

Keywords: Stir bar sorptive extraction; Water analysis; Pesticides; PAHs; Method validation; GC–MS

Method for rapid conjugation of recombinant photoprotein aequorin with streptavidin and application as a universal detection reagent for binding assays by Panayotis G. Zerefos; Penelope C. Ioannou; Theodore K. Christopoulos (pp. 267-273).

A binding assay utilizes the highly specific molecular recognition properties of a biological macromolecule, e.g. an antibody, receptor or DNA/RNA probe for the detection/quantification of a target analyte in a complex mixture. The recognition event is linked to a signal-producing system. Because biomolecules can be easily labeled with biotin, the biotin–streptavidin interaction has been established as a general system for linking molecular recognition with signal generation. To this end, we report a rapid and simple method for conjugation of the highly detectable recombinant photoprotein aequorin with streptavidin, thus generating a universal reagent for binding assays. The method is based on the use of aequorin fused to a hexahistidine tag at the amino terminus. Thiol groups were introduced to aequorin whereas streptavidin was derivatized with maleimide groups. The conjugate was purified in a single step by immobilized metal ion affinity chromatography, thus avoiding laborious chromatographic procedures. The performance of aequorin–streptavidin conjugate was tested in a DNA hybridization assay as a model. The limit of detection was 0.3pmoll⁻¹ and the analytical range extended up to 500pmoll⁻¹. The CV was about 8%. Besides the high detectability, the assay is rapid (completed in just 25min) due to the flash-type (3s) bioluminescent reaction of aequorin, which avoids substrate incubation steps that are common to binding assays employing enzyme labels.

Keywords: Aequorin; Streptavidin; Conjugation; Affinity separation; Bioluminescence; Hybridization

Data fusion and dual-domain classification analysis of pigments studied in works of art by Pablo Manuel Ramos; Itziar Ruis�nchez (pp. 274-282).

We propose a new mid-level data-fusion system to process, as a unique signal, the Raman and X-ray fluorescence (XRF) spectra obtained from the first micro-Raman–XRF instrument. The system is based on the main advantage of the wavelet transform, which is multiresolution. First, each spectrum set is split into blocks according to their frequency. The blocks which contains background and noise signals are removed and variable selection is performed on the remaining blocks to extract those variables with the most power of classification. These variables are concatenated and form a Raman–XRF meta-signal ensemble. Finally, dual-domain signal ensembles from references and samples are classified using partial least squares discriminant analysis (PLS-DA). Our results show that this system is suitable for rapidly and automatically classifying ancient pigments using the complementary information provided by both techniques. Classification with different levels of difficulty can be handled and no prior knowledge of the sample composition is required. This system has been applied to real spectra of ancient pigments and can also be applied to combinations of other spectral signals.

Keywords: Data fusion; Wavelet transform; Dual-domain partial least squares discriminant analysis (DDPLS-DA); Micro-Raman spectroscopy; Micro-X-ray fluorescence spectrometry; Ancient pigments

The suitability of XRF analysis for compositional classification of archaeological ceramic fabric: A comparison with a previous NAA study by R. Padilla; P. Van Espen; P.P. Godo Torres (pp. 283-289).

The main drawbacks of EDXRF techniques, restricting its more frequent use for the specific purpose of compositional analysis of archaeological ceramic fabric, have been the insufficient sensitivity to determine some important elements (like Cr, REE, among others), a somewhat worse precision and the inability to perform standard-less quantitative procedures in the absence of suitable certified reference materials (CRM) for ceramic fabric. This paper presents the advantages of combining two energy dispersive X-ray fluorescence methods for fast and non-destructive analysis of ceramic fabric with increased sensitivity. Selective polarized excitation using secondary targets (EDPXRF) and radioisotope excitation (R-XRF) using a²⁴¹Am source. The analytical performance of the methods was evaluated by analyzing several CRM of sediment type, and the fitness for the purpose of compositional classification was compared with that obtained by using Instrumental Neutron Activation Analysis in a previous study of Cuban aborigine pottery.

Keywords: Energy dispersive X-ray fluorescence analysis; Compositional classification; Archaeological pottery

Development of a highly sensitive, second antibody format chemiluminescence enzyme immunoassay for the determination of 17β-estradiol in wastewater by Lixia Zhao; Jin-Ming Lin; Zhenjia Li; Xitang Ying (pp. 290-295).

In the present work, a highly sensitive chemiluminescence enzyme immunoassay (CLEIA) method for the determination of 17β-estradiol (E2) in the wastewater was developed, which used the fluorescein- iso-thiocyanate (FITC)–anti-FITC system as solid phase and the biotin–streptavidin system as signal amplification system, with the highly sensitive 4-methoxy-4-(3-phosphatephenyl)-spiro-(1,2-dioxetane-3,2′-adamantane) (AMPPD)–alkaline phosphatase (ALP) system as chemiluminescence detection system. The specific polyclonal antibody was produced against a conjugate of estradiol–bovine serum albumin (BSA), biotinoyl–diaminodioxaoctane–estradiol conjugate was synthesized. The specificity of anti-E2 antibody was also studied. The results showed that anti-E2 antibody has no cross-reactions for estriol, ethinyl E2, estrone commonly coexisting with E2 in the wastewater. Samples were prepared with solid-phase extraction using C₁₈ cartridges for the removal of matrix effects. The linear range was 2.5–1600pgml⁻¹ and detection limit was 1.5pgml⁻¹. As our known of knowledge, the method was more sensitive for the determination of E2 in water compared with other immunoassay methods. Recoveries were in the range of 80–110% in spiked tap water and wastewater. This method has been successfully used for the detection of E2 in wastewater, compared with the commercially radioimmunoassay (RIA) kit, the correlation was good.

Keywords: 17β-Estradiol; Fluorescein-; iso; -thiocyanate (FITC)–anti-FITC system; Chemiluminescence immunoassay; Wastewater

In vitro monitoring of nanogram levels of naproxen in human urine using flow injection chemiluminescence by Xianglei Cheng; Lixia Zhao; Meilin Liu; Jin-Ming Lin (pp. 296-301).

Based on the synergic effect of the hydrophobicity of sodium dodecylbenzenesulfonate (SDBS) micelles and the incorporation of naproxen molecules, a simple, rapid and sensitive chemiluminescence (CL) method was described for the determination of naproxen in pharmaceuticals and urine. Under the optimum experimental conditions, the CL intensity was linear over the concentration of naproxen ranging from 1.0 to 700.0ngmL⁻¹ ( r=0.9917) with a detection limit as low as 0.9ngmL⁻¹ (S/N=3). The mechanism of CL was discussed in detail based on the spectrometry. The experimental results demonstrated that the excretive amounts of naproxen reached its maximum in 4.0h after taking 200mg naproxen tablet; and the naproxen excretive ratio during 8.0h was 5.46% in the body of volunteers.

Keywords: Chemiluminescence; Naproxen; Urine; Flow injection analysis

Hot electron-induced time-resolved electrogenerated chemiluminescence of a europium(III) label in fully aqueous solutions by Q. Jiang; M. H�kansson; A.-M. Spehar; J. Ahonen; T. Ala-Kleme; S. Kulmala (pp. 302-309).

Time-resolved electrogenerated chemiluminescence of multidentate phenolic Eu(III) chelates were studied in aqueous solution. 2,6-bis[ N, N-bis(carboxymethyl)-aminomethyl]-4-benzoylphenol forms a photoluminescent and electrochemiluminescent Eu(III) chelate, whereas 2,6-bis[ N, N-bis(carboxymethyl)-aminomethyl]-4-methyl phenol-chelated Eu(III) turned out to be not luminescent at all. The importance of the redox properties of both the ground and the excited states of the ligands and the central ion is shown. The former chelate shows relatively weak ECL at an oxide-covered aluminum electrode but the ECL intensity can be strongly enhanced by the addition of peroxodisulfate ions. In the presence of 1mM peroxodisulfate ions the ECL lifetime of this chelate is 0.94ms, thus easily allowing time-resolved detection of the chelate. This chelate can be conjugated to antibodies by thioureido linkage and used as an electrochemiluminescent label in immunoassays as a marker which displays long-lived luminescence in the red end of the optical spectrum. The present ECL is mainly based on the ligand sensitized redox excitation of the chelate by analogous pathways to those known from the studies of aromatic Tb(III) chelates but the energy transfer from the emission centers of the aluminum oxide film can also have minor contribution to the excitation of the label.

Keywords: Bioaffinity assays; Immunoassays; Time-resolved detection; Lanthanide chelates; Electrochemiluminescence

Automatic method for determination of total antioxidant capacity using 2,2-diphenyl-1-picrylhydrazyl assay by Lu�s M. Magalh�es; Marcela A. Segundo; Salette Reis; Jos� L.F.C. Lima (pp. 310-318).

In the present work, an automatic method based on multi-syringe flow injection analysis (MSFIA) was developed for the determination of total antioxidant capacity, measured as the cumulative capacity of the compounds present in the sample to scavenge free radicals, using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) reaction. The determination is based on the colour disappearance due to the scavenging of DPPH by antioxidant compounds monitored spectrophotometrically at 517nm.The influence of initial DPPH concentration and sample dilution in the present methodology was studied. It was verified that the amount of DPPH consumed by antioxidant standards (ascorbic and caffeic acids) was independent of the initial concentration of radical except for situations where DPPH/antioxidant molar ratio was lower than the stoichiometric value. Furthermore, the sample dilution factor plays an important role for achieving results comparable to those from end-point batch method since the exhausting of scavenging ability of the sample should take place during the period of absorbance measurement.The proposed method was applied to several food products and the total antioxidant capacity was expressed as Vitamin C equivalent antioxidant capacity (VCEAC). The results obtained by the proposed method ranged from 1.1 to 318mg of ascorbic acid/100ml and they were statistically comparable to those provided by the batch method. The detection limit was 0.34mg of ascorbic acid/100ml and the determination frequency was about 13h⁻¹ with an excellent repeatability (R.S.D.<1%, n=10).

Keywords: Total antioxidant capacity; DPPH; Multi-syringe flow injection; Beverages

Aracyl triflates for preparing fluorescent and UV absorbing derivatives of unreactive carboxylates, amines and other metabolites by Malina K. Storer; Michael Lever (pp. 319-325).

Aracyl trifluoromethanesulfonate (triflate) reagents alkylate the unreactive carboxyl groups of betaines. The reagents also derivatise tertiary amines, amine oxides, phosphates and thioethers. A general derivatisation procedure is to dilute the sample with a polar aprotic organic solvent containing a trace of water, followed by adding an appropriate base and the aracyl triflate reagent. Limits of detection were 40nM for glycine betaine (GB) and carnitine, 0.14μM for N, N-dimethylglycine, 70nM for trimethylamine (TMA), and 5.9μM trimethylamine- N-oxide (TMAO). Limits of detection were improved when derivatisation yield was optimised for different analytes by changing solvent, base and water content of the reaction mixture. Solvents used include acetonitrile, acetone, butanone, dimethoxyethane and dimethoxyethyl ether, with the presence of some water or alcohol tolerated. Suitable bases include the inorganic bases magnesium hydroxide, silver oxide and lithium phosphate. These bases are sparingly soluble in the reaction solvent so sustain weakly basic conditions during derivatisation and can be removed by centrifugation to stop the reaction. This is particularly important for betaine assays since the derivatives are base-sensitive. The information presented here can be used to develop assays for many metabolites using these versatile reagents.

Keywords: Aracyl trifluoromethanesulfonate; Betaine; Trimethylamine

A new method of histamine colorimetry using 2,3-naphthalenedicarboxaldehyde on a silica–gel column cartridge by Shigeyuki Oguri; Aki Mizusawa; Maiko Kamada; Minako Kohori (pp. 326-331).

In our work, we found, by chance, that 2,3-naphthalenedicarboxaldehyde (NDA) acts as a color development reagent to histamine (HA) in the absence of a reductant, e.g., cyanide anion, even in a weakly acidic environment. The NDA-induced color development reaction to HA shows the maximum absorption of 552nm at pH 6 after a minimal interval of 10min. By using this chemical property, a simple and convenient new method of visual colorimetry of HA on a short silica–gel column cartridge (called an “HA cartridge�? in this study, which consisted of 50mg of silica–gel packed into a 1.0ml disposable syringe) was developed. The new visual method involves extraction of a 5g sample with 5% trichloroacetic acid solution (TCA, 35ml), followed by neutralizing with 1M sodium hydroxide. After loading the TCA extract (500μl) into the HA cartridge, the cartridge was then washed with a 0.1M phosphate buffer, pH 6 (200μl) and water (200μl×3 times). When a solution of 1mM NDA in acetonitrile (200μl) was passed through the HA cartridge, the color inside the cartridge was observed to changed at 3min after the NDA loading from white to indigo-blue, for concentrations of HA ranging from 25 to 1000mgkg⁻¹. This sequence requires only 5min to perform.

Keywords: Allergy-like food poisoning; Colorimetry; Histamine; Histamine poisoning; 2,3-Naphthalenedicarboxaldehyde

Application of X-ray absorption near-edge structure (XANES) using bent crystal analyzer to speciation of trace Os in iron meteorites by Yoshio Takahashi; Tomoya Uruga; Hajime Tanida; Yasuko Terada; Shun’ichi Nakai; Hiroshi Shimizu (pp. 332-336).

X-ray absorption near-edge structure (XANES) spectroscopy at the Os L_III-edge was measured for the speciation of trace Os in two iron meteorites, Negrillos and Bennett County, which contain 65.7 and 58.3mg/kg of Os, respectively, while major elements, Fe+Ni, are more than 95wt.%. During Os XANES measurement, intense Fe–K and Ni–K fluorescence and scattered X-rays existed as background noise, which were more than four orders higher than Os Lα fluorescence. To reject the unwanted X-rays, a log spiral bent crystal analyzer in Bragg geometry for X-ray fluorescence detection combined with a single-element pure Ge detector and slits was used. The system enabled us to obtain the Os L_III-edge XANES spectra of the two iron meteorites with greater quality compared with those recorded in a conventional fluorescence mode by a 19-element Ge detector without analyzer crystals. In addition, a commercially available crystal analyzer (BCLA, Oxford danfysik) in Laue geometry was also tested, and it also gave similar high-quality XANES spectra. The Bragg geometry reduced the noise due to background X-rays more effectively than the Laue system, while the Laue geometry was efficient to collect target fluorescence X-ray, suggesting that a better spectrum in terms of statistics could be obtained using a Laue analyzer coupled with a multi-element Ge detector with a large acceptance area for fluorescence detection. The reliable spectral shape of XANES measured enabled us to simulate XANES spectra of Os in iron meteorites in a highly quantitative manner. A system using log spiral crystal analyzer coupled with a Ge detector is a powerful tool for the speciation of trace elements in natural minerals and rocks.

Keywords: X-ray absorption near-edge structure (XANES); Crystal analyser; Speciation; Osmium

Nucleation monitoring in cooling crystallization with a quartz crystal oscillator by Kouji Maeda; Byoung Chul Kim; Young Han Kim; Keisuke Fukui (pp. 337-344).

A crystallization monitoring system using a quartz crystal oscillator was implemented in the cooling crystallization of dilute lauric acid solutions for the investigation of the nucleation process of the solute. In addition, the microscopic observation of the oscillator surface was conducted to examine the number and size of yielded nuclei, and the observed results and the resonant frequency variation of the oscillator were analyzed to explain the nucleation process.The change of the resonant frequency indicated the beginning moments of emulsification and nucleation of lauric acid near the oscillator surface. The experimental results show that the average crystal size was raised from 139 to 238nm and the nucleation rate was reduced as the solution concentration increased from 0.05 to 0.25g/L. When the solution temperature lowers, the crystal grows more rather than new nuclei form in the high concentration solution. The estimated crystal mass from microscopic observation ranges between 18% and 28% of that from the frequency measurement. It was also demonstrated that the proposed monitoring device is useful to investigate the crystallization process in dilute solutions, which often requires large analytical instruments.

Keywords: Nucleation; Crystallization; Quartz crystal Oscillator; Resonant frequency

Author Index (pp. 345-347).

Sections

Personal tools

Analytica Chimica Acta (v.558, #1-2)

Sections

Personal tools

Local resources

Analytica Chimica Acta (v.558, #1-2)