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Analytical and Bioanalytical Chemistry (v.382, #2)

Euroanalysis XIII: The European Conference on Analytical Chemistry by Jesús Hernández Méndez; José Luis Pérez Pavón (pp. 243-244).

European Analytical Column No. 33 (January 2005) by Miguel Valcárcel; Ernst-Heiner Korte (pp. 245-247).

On-line FT-Raman and dispersive Raman spectra database of artists’ materials (e-VISART database) by K. Castro; M. Pérez-Alonso; M. D. Rodríguez-Laso; L. A. Fernández; J. M. Madariaga (pp. 248-258).

Raman spectroscopy has been widely applied in the analysis of different types of artwork. This technique is sensitive, reliable, non-destructive and can be used in situ. However, there are few references in the literature regarding specific Raman spectra libraries for the field of artwork analysis. In this paper, the development of two on-line databases with Fourier transform Raman (FT-Raman; 1064 nm) and dispersive Raman (785 nm) spectra of materials used in fine art is presented; both are implemented in the e-vibrational spectroscopic databases of artists’ materials database (e-VISART). The database provides not only spectra, but also information about each pigment. It must be highlighted that for each pigment or material several spectra are available from different dealers. Some of the FT-Raman spectra available in the e-VISART database have not been published until now. Some examples in which the e-VISART database has been successfully used are presented.

Keywords: Pigment; Database; Raman; Library; Spectra

Identification of natural dyes used in works of art by pyrolysis–gas chromatography/mass spectrometry combined with in situ trimethylsilylation by María José Casas-Catalán; María Teresa Doménech-Carbó (pp. 259-268).

Samples of four natural dyes from different organic families—natural madder (anthraquinonoid), curcuma (curcuminoid), saffron (carotenoid) and indigo (indigotic)—were analysed using a new procedure based on pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS), which includes the on-line derivatisation of the natural dyes using hexamethyldisilazane (HMDS). In addition, a previous procedure involving the addition of a 10% H₂SO₄ aqueous solution to the dye and further separation with ethyl acetate has been tested. This procedure enhances the sensitivity of the method by extracting the colouring compounds from the rest of the compounds present in the natural dye. Two possible derivatising reagents—HMDS and tetramethylammonium hydroxide (TMAH)—were compared in order to assess their effectiveness in the proposed method. Characteristic peaks from trimethylsilyl derivatives of alizarin, quinizarin, xanthopurpurin and purpurin were obtained for madder; peaks from safranal, isophorone and trimethylsilyl derivative of crocetin for saffron; peaks from 4-(4-hydroxy-3-methoxy)phenyl-3-buten-2-one and 4-(4-hydroxy-3-methoxy)phenyl-2-butanone, which are primary pyrolysis products of curcuma, and peaks from indole, 2-methylindole and 2,3-dihydroindol-2-one, which are primary pyrolysis products of indigo, among others, were obtained. The reported procedure leads to the unambiguous identification of the four studied dyes from solid samples formed by individual dyes.

Keywords: Madder; Saffron; Curcuma; Indigo; Py–GC/MS; Hexamethyldisilazane; Tetramethylammonium hydroxide

Earth pigments in painting: characterisation and differentiation by means of FTIR spectroscopy and SEM-EDS microanalysis by C. Genestar; C. Pons (pp. 269-274).

Analytical characterisation of natural earths (ochres, siennas, umbers and green earths) has been carried out using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) coupled to an energy dispersive X-Ray spectrometer (EDS). The study of these pigments, which are found in works of art, is very important since it can shed light on their source or the pictorial technique used. FTIR spectroscopy is suitable for the identification and differentiation of ochres and siennas. According to the matrix of the sample, FTIR allows the classification of ochres into ochres containing kaolinite and ochres containing sulphate. One of the goals of this research has been to establish a relationship between the matrix and the source of the samples tested. SEM-EDS is probably a better technique than FTIR for characterising umbers and green earths since they do not exhibit significant differences when FTIR studies are performed.

Keywords: Ochres; Siennas; Umbers and green earths; SEM-EDS; FTIR; Works of art

Analysis of organic colouring and binding components in colour layer of art works by S. Kuckova; I. Nemec; R. Hynek; J. Hradilova; T. Grygar (pp. 275-282).

Two methods of analysis of organic components of colour layers of art works have been tested: IR microspectroscopy of indigo, Cu-phthalocyanine, and Prussian blue, and MALDI-TOF-MS of proteinaceous binders and a protein-containing red dye. The IR spectra distortion common for smooth outer surfaces and polished cross sections of colour layer of art works is suppressed by reflectance measurement of microtome slices. The detection limit of the three blue pigments examined is ~0.3 wt% in reference colour layers in linseed oil binder with calcite as extender and lead white as a drying agent. The sensitivity has been sufficient to identify Prussian blue in repaints on a Gothic painting. MALDI-TOF-MS has been used to identify proteinaceous binders in two historical paintings, namely isinglass (fish glue) and rabbit glue. MALDI-TOF-MS has also been proposed for identification of an insect red dye, cochineal carmine, according to its specific protein component. The enzymatic cleavage with trypsin before MALDI-TOF-MS seems to be a very gentle and specific way of dissolution of the colour layers highly polymerised due to very long aging of old, e.g. medieval, samples.

Keywords: Proteins; Binders; Blue dyes; Painting; MALDI

An extensive colour palette in Roman villas in Burgos, Northern Spain: a Raman spectroscopic analysis by S. E. J. Villar; H. G. M. Edwards (pp. 283-289).

Seventy-five specimens from thirty fragments of Roman villa wall-paintings from sites in Burgos Castilla y Leon, Spain, have been analysed by Raman spectroscopy. This is the first time that a Raman spectrocopic study of Roman wall-paintings from Spain has been reported. The extensive range of tonalities and colour compositions contrasts with the results found in other provinces of the Roman Empire, for example Romano-British villas. Calcite, aragonite, haematite, caput mortuum, cinnabar, limonite, goethite, cuprorivaite, lazurite, green earth, carbon and verdigris have been found as pigments. Some mineral mixtures with different tonalities have been made using different strategies to those more usually found. Of particular interest is the assignation of the Tarna mine for the origin of the cinnabar used for obtaining the red colour in some specimens analysed here. The wide range of colours, tonalities and minerals found in some of the sites studied in this work is suggestive of a high social status for the community.

Keywords: Raman spectroscopy; Roman villa; Pigment; Wall-painting; Mineral

Development and validation of a novel HPLC/ELSD method for the direct determination of tobramycin in pharmaceuticals, plasma, and urine by Nikolaos C. Megoulas; Michael A. Koupparis (pp. 290-296).

A novel method for the direct determination of the aminoglycoside tobramycin was developed and validated based on reversed-phase high-performance liquid chromatography (RP-HPLC) with evaporative light scattering detector (ELSD). Using a Waters ODS-2 C18 Spherisorb column with an evaporation temperature of 45°C and nitrogen pressure of 3.5 bar, the selected mobile phase consisted of water/acetonitrile 55:45 containing 1.5 mL L⁻¹ HFBA (11.6 mM) in an isocratic mode at a rate of 1.0 mL min⁻¹. Tobramycin’s retention time was 4.3 min with an asymmetry factor of 1.7. A logarithmic calibration curve was obtained from 1 to 38 μg mL⁻¹ (r > 0.9998). LOD was 0.3 μg mL⁻¹; within-day %RSD was 1.0 (n = 3, 4.7 μg mL⁻¹) and between-day %RSD was 1.1 (3 days within a week). The developed method was applied to the determination of tobramycin in a pharmaceutical crude substance and formulations (eye drops and ointments). Dilution experiments revealed the absence of interference from excipients (no constant and proportional errors); recovery from spiked samples was 99–103% with %RSD < 2.2 (n = 3×3). The developed HPLC/ELSD method was also found to be applicable in the determination of tobramycin in human plasma (0.6–12.5 μg mL⁻¹) and urine (1.5–12.5 μg mL⁻¹) after solid-phase extraction using carboxylate cartridges followed by solvent evaporation (×2 preconcentration). A mean recovery of 86% for plasma and 91% for urine was obtained.

Keywords: Evaporative light scattering; ELSD; Tobramycin; HPLC; Aminoglycosides; Pharmaceuticals; Plasma; Urine

Amperometric detection in TMB/HRP-based assays by Pablo Fanjul-Bolado; María Begoña González-García; Agustín Costa-García (pp. 297-302).

3,3′,5,5′-Tetramethylbenzidine (TMB) is the most commonly used chromogen for horseradish peroxidase (HRP) and so its performance as an electrochemical substrate was evaluated. Measurements of HRP activity in solution were carried out by using an amperometric detector coupled to a flow injection analysis (FIA) system. The enzymatic product was easily detected at a potential of +0.1 V (vs. Ag-pseudoreference electrode) at a bare screen-printed electrode placed in a homemade electrochemical flow cell. A high flow rate (4.3 mL min⁻¹) of 0.5 M H₂SO₄ was used to obtain repeatable signals and a short analysis time. The detection limit achieved after 15 min of incubation was 2×10⁻¹⁴ M of HRP. The applicability of the amperometric detector to ELISAs was demonstrated by using a commercially available kit for the quantification of interleukin-6 (IL-6) without modifying the kit manufacturer’s protocol or the reagents for this test.

Keywords: Horseradish peroxidase; 3,3′,5,5′-Tetramethylbenzidine; Screen-printed carbon electrode; Flow injection analysis; ELISA

Amperometric PMMA-microchip with integrated gold working electrode for enzyme assays by Mario Castaño-Álvarez; M. Teresa Fernández-Abedul; Agustín Costa-García (pp. 303-310).

The use of a gold film in-channel detector combined with a poly(methyl methacrylate) (PMMA) CE microchip has been tested for alkaline phosphatase (AP) enzymatic assays. Tris-borate or Tris-Gly (pH 9.0, 50 mmol L⁻¹) buffer solutions were appropriate as running buffer. Signals for three common AP products: α-naphthol, p-nitrophenol, and ascorbic acid, were obtained. They were reproducible (RSD 4.4% for six successive electropherograms corresponding to 5 mmol L⁻¹ α-naphthol solution) and the response was dependent on concentration (linear relationship for ascorbic acid solutions between 5 and 20 mmol L⁻¹ concentration). Use of an end-channel gold film electrode was also investigated. If one of the reagents (substrate or enzyme) is included in the running buffer, two different types of enzymatic assay are feasible in less than 3 min.

Keywords: Microchip; Electrochemical detection; In-channel; Gold film; Enzyme assay

Classifying honeys from the Soria Province of Spain via multivariate analysis by M. J. Nozal Nalda; J. L. Bernal Yagüe; J. C. Diego Calva; M. T. Martín Gómez (pp. 311-319).

A total of 73 different honeys from seven botanical origins [ling (Calluna vulgaris L.), heather (Erica sp.), rosemary (Rosmarinus officinalis L.), thyme (Thymus vulgaris L.), honeydew (Quercus sp.), spike lavender (Lavandula latifolia M.) and french lavender (Lavandula stoechas L.)] have been classified by applying discriminant analysis to their metal content data and other common physicochemical parameters. Fifteen minerals were identified and quantified using atomic emission spectroscopy (AES) for K and Na, and inductively coupled plasma atomic emission spectrometry (ICP-AES) for Mg, Ca, Al, Fe, Mn, Zn, B, Cu, Co, Cr, Ni, Cd and Pb. Moreover, eight physicochemical parameters were analysed following the Harmonised Methods of the International Honey Commision: ash content, moisture, insoluble matter, reducing sugars, apparent sucrose, diastase activity, free acidity and hydroxymethylfurfural. The honeys analysed were characterised and distinguished using chemometrics. ANOVA highlighted significant differences between the honeys in terms of the mean contents of all variables except apparent sucrose, HMF, Fe and Zn. Principal component analysis was used as a descriptive tool to visualise the data structure in two dimensions, finding relationships between variables and types of honey. Likewise, discriminant analysis, together with various methods (stepwise, forward and backward), was used to select the variables with the highest discriminating power, which allowed us to classify all of the botanical origins considered in this work, achieving a global success rate close to 90% following cross-validation.

Keywords: Honey; Mineral content; Physicochemical parameters; Chemometrics; Discriminant analysis

Robust and non-parametric statistics in the evaluation of figures of merit of analytical methods. Practices for students by M. Cruz Ortiz; Ana Herrero; Silvia Sanllorente; Celia Reguera (pp. 320-327).

A set of laboratory practices is proposed in which evaluation of the quality of the analytical measurements is incorporated explicitly by applying systematically suitable methodology for extracting the useful information contained in chemical data. Non-parametric and robust techniques useful for detecting outliers have been used to evaluate different figures of merit in the validation and optimization of analytical methods. In particular, they are used for determination of the capability of detection according to ISO 11843 and IUPAC and for determination of linear range, for assessment of the response surface fitted using an experimental design to optimize an instrumental technique, and for analysis of a proficiency test carried out by different groups of students. The tools used are robust regression, least median of squares (LMS) regression, and some robust estimators as median absolute deviation (m.a.d.) or Huber estimator, which are very useful as an alternatives to the usual centralization and dispersion estimators.

Keywords: Proficiency test; Non-parametric statistics; Least median of squares regression; Linear range; Capability of detection; Experimental design

Use of multivariate curve resolution for determination of chromium in tanning samples using sequential injection analysis by V. Gómez; M. P. Callao (pp. 328-334).

We report a method for determining total chromium in tanning samples using sequential injection analysis (SIA) with a diode-array spectrophotometric detector. With a suitable analytical sequence CrO₄^2– is converted to Cr₂O₇^2– inside the tubes of the SIA system, after total oxidation of chromium(III). A data matrix is obtained and analysed by several chemometric techniques based on multivariate analysis: principal components analysis, simple-to-use interactive self-modelling mixture analysis, and multivariate curve resolution-alternating least-squares. We studied several samples from different stages of a tanning process. Two of these samples were easily oxidized but the others needed more extreme conditions. The analytical sequence prepared, which was based on obtaining a pH gradient and used H₂SO₄ as reagent, is valid and independent of the level of oxidation needed for the sample. We established a calibration model and evaluated the figures of merit. In some samples we found interferents. With this method the amounts of chromium in each sample were quantified and the results were statistically similar to those obtained by use of the reference method, atomic absorption spectrometry.

Keywords: Chromium; SIA; MCR; Tanning sample

Extraction procedures for chemical speciation of arsenic in atmospheric total suspended particles by Vanesa Oliveira; José Luis Gómez-Ariza; Daniel Sánchez-Rodas (pp. 335-340).

An arsenic chemical speciation study was performed in 2000, using air filters on which total suspended particles (TSP) were collected, from the city of Huelva, a medium size city with huge industrial influence in SW Spain. Different procedures for extraction of the arsenic species were performed using water, NH₂OH.HCl, and H₃PO₄ solutions, with either microwave or ultrasonic radiation. The best optimised extraction methods were use of 100 mmol L⁻¹ NH₂OH.HCl and 10 mmol L⁻¹ H₃PO₄ and microwave radiation for 4 min. High-performance liquid chromatography coupled with hydride generation and atomic fluorescence spectrometry (HPLC–HG–AFS) was employed for determination of the arsenic species. The results from 12 TSP air filters collected on a monthly basis showed extraction was quantitative (94% with NH₂OH.HCl and 86% H₃PO₄). Only inorganic arsenic species (arsenite and arsenate) were detected. The mean arsenite concentration was 1.2±0.3 ng m⁻³ (minimum 0.3 ng m⁻³, maximum 1.8 ng m⁻³). The mean arsenate concentration was 10.4±1.8 ng m⁻³, with greater monthly variations than arsenite (minimum 2.1 ng m⁻³, maximum 30.6 ng m⁻³). The high level of arsenic species in the TSP samples can be related to a copper smelter located in the region.

Keywords: Arsenic; Extraction; Chemical speciation; Air filter; TSP

Detection of 2,4,6-trichloroanisole in chlorinated water at nanogram per litre levels by SPME–GC–ECD by Paula B. M. Pinheiro; Joaquim C. G. Esteves da Silva (pp. 341-346).

A method involving solid-phase micro extraction (SPME) and gas chromatography with electron capture detection (SPME–GC–ECD) has been optimised for identification and quantification of 2,4,6-trichloroanisole (TCA) at ng L⁻¹ concentrations in disinfected (chlorinated) water samples. A central composite design was used for factorial analysis of four factors, three factors related to the SPME (PDMS fibre) procedure (adsorption time, temperature of the sample during headspace sampling, and desorption time) and one related to the GC operation (the rate of increase of the temperature of the GC oven). Good linearity (linear correlation coefficient greater than 0.999) was observed for TCA concentrations up to 50 ng L⁻¹, limits of detection and quantification of 0.7 and 2.3 ng L⁻¹, respectively, and good precision (relative standard deviation 2.8% and 3.4% for 5 and 30 ng L⁻¹ of TCA, respectively). Besides TCA, this system also enables the detection and quantification of the four trihalomethanes in the μg L⁻¹ concentration range with limits of detection and quantification of approximately 0.3 μg L⁻¹ and 1 μg L⁻¹, respectively.

Keywords: 2,4,6-Trichloroanisole (TCA); Trihalomethanes (THM); Chlorination; Water; Disinfection by-products.

Use of ICP and XAS to determine the enhancement of gold phytoextraction by Chilopsis linearis using thiocyanate as a complexing agent by Jorge L. Gardea-Torresdey; Elena Rodriguez; Jason G. Parsons; Jose R. Peralta-Videa; George Meitzner; Gustavo Cruz-Jimenez (pp. 347-352).

Under natural conditions gold has low solubility that reduces its bioavailability, a critical factor for phytoextraction. Researchers have found that phytoextraction can be improved by using synthetic chelating agents. Preliminary studies have shown that desert willow (Chilopsis linearis), a common inhabitant of the Chihuahuan Desert, is able to extract gold from a gold-enriched medium. The objective of the present study was to determine the ability of thiocyanate to enhance the gold-uptake capacity of C. linearis. Seedlings of this plant were exposed to the following hydroponics treatment: (1) 5 mg Au L⁻¹ (2.5×10⁻⁵ mol L⁻¹), (2) 5 mg Au L⁻¹+10⁻⁵ mol L⁻¹ NH₄SCN, (3) 5 mg Au L⁻¹+5×10⁻⁵ mol L⁻¹ NH₄SCN, and (4) 5 mg Au L⁻¹+10⁻⁴ mol L⁻¹ NH₄SCN. Each treatment had its respective control. After 2 weeks we determined the effect of the treatment on plant growth and gold content by inductively coupled plasma–optical emission spectroscopy (ICP–OES). No signs of shoot-growth inhibition were observed at any NH₄SCN treatment level. The ICP–OES analysis showed that addition of 10⁻⁴ mol L⁻¹ NH₄SCN increased the concentration of gold by about 595, 396, and 467% in roots, stems, and leaves, respectively. X-ray absorption spectroscopy (XAS) studies showed that the oxidation state of gold was Au(0) and that gold nanoparticles were formed inside the plants.

Keywords: Gold; PhytoextractionChilopsis linearisICP–OES; XAS; Complexing agents

Effect of chloride on heavy metal mobility of harbour sediments by A. Guevara-Riba; A. Sahuquillo; R. Rubio; G. Rauret (pp. 353-359).

To evaluate the environmental impact of polluted sediments, several operationally defined sequential extraction procedures (SEPs) have been described. Salinity has long been recognised as an important variable determining the physicochemical behaviour of heavy metals in marine sediments. Thus, in the present paper, the modified BCR-SEP has been applied to harbour sediments in order to assess to what extent trace metal mobility (Cd, Cr, Cu, Ni, Pb and Zn) could be influenced by chloride content in sediments. For this, washed (W) and non-washed (NW) sediments were compared. The relative mobility order observed for the six trace metals studied was not seen to be influenced by the presence of chloride in the sediments, but an increase of mobility was observed for Cd and Zn (the most mobile metals) when chloride was present in the sediments. Characterisation of the sediments and of the pseudo-total metal contents by means of an aqua regia extraction was also assessed.

Keywords: Sequential extraction procedure; Trace metals; Mobility; Chloride content

Copper, nickel, and vanadium in the Western Galician Shelf in early spring after the Prestige catastrophe: is there seawater contamination? by Juan Santos-Echeandía; Ricardo Prego; Antonio Cobelo-García (pp. 360-365).

The original cargo fuel transported by the Prestige tanker, according to our analysis, contained several trace elements, for example Cu (3 μg g⁻¹), Ni (97 μg g⁻¹), and V (382 μg g⁻¹). The possibility of metal contamination of seawater near the bottom from the sedimented fuel and in surface waters from the fuel deposited on the littoral area was researched in the Western Galician Shelf 5 months after the Prestige shipwreck (November 2002). Water samples obtained at eight stations from Finisterre Cape to Miño River were analysed by means of an electroanalytical method (AdCSV) and following trace-metal-clean procedures. Only the surface Cu and Ni levels at the Ons and Cíes Islands were higher than those considered as background for Open North East Atlantic Ocean waters. The accumulation and weathering of the fuel deposited on the shores could be a significant source for the enrichment found, but the influence of industrial and urban inputs from the neighbouring Pontevedra and Vigo rias is also possible. Thus, this study was useful for establishing typical values of Cu, Ni, and V in Galician Shelf waters for the first time. Total metal concentrations ranged between 1.7 and 3.4 nmol L⁻¹ for Cu, between 2.9 and 4.8 nmol L⁻¹ for Ni, and between 19.7 and 32.3 nmol L⁻¹ for V; dissolved concentrations were between 0.7 and 1.5 nmol L⁻¹ for Cu, between 2.2 and 3.3 nmol L⁻¹ for Ni, and between 15.5 and 27.0 nmol L⁻¹ for V; particulate values below 2.6 nmol L⁻¹ for Cu, 2 nmol L⁻¹ for Ni, and 7.2 nmol L⁻¹ for V were obtained.

Keywords: Metals; Contamination; Seawater; Oil-spillPrestigeGalician Shelf

A rapid and sensitive GC–MS method for determination of 1,3-dichloro-2-propanol in water by Rainer Schuhmacher; Johanna Nurmi-Legat; Andreas Oberhauser; Markus Kainz; Rudolf Krska (pp. 366-371).

A rapid analytical method for sensitive determination of 1,3-dichloro-2-propanol (1,3-DCP) in river water has been developed. 1,3-DCP is extracted from water with ethyl acetate. After filtration through sodium sulfate the ethyl acetate phase is analyzed by gas chromatography–mass spectrometry. The method uses 1,3-DCP-d₅ as internal standard. Different extraction solvents, concentrations of ammonium sulfate in the water samples, and the effect of humic acid were tested and their influence on the recovery of DCP has been evaluated. The method quantification limit was 0.1 μg L⁻¹. For spiked water samples (0–5.2 μg L⁻¹, n=21) a repeatability coefficient of variation of 5.4% was obtained. The average recovery rate of 1,3-DCP was 105±3% (n=21). Stability tests, which were carried out with Danube river water, led to an estimated 1,3-DCP degradation rate of 0.008±0.0008 day⁻¹ at 6°C.

Keywords: Dichloropropanol; Water; Gas chromatography; Mass spectrometry

Factors affecting signal intensity in headspace mass spectrometry for the determination of hydrocarbon pollution in beach sands by Miguel del Nogal Sánchez; José Luis Pérez Pavón; M. Esther Fernández Laespada; Carmelo García Pinto; Bernardo Moreno Cordero (pp. 372-380).

One of the main limitations to the use of direct coupling of headspace mass spectrometry (HS-MS) for the quantitative determination of analytes in a sample is related to factors affecting the signal intensity. The importance of strategies aimed at compensating this problem is considerable in the case of classification, and is indeed critical as regards the problems involved in quantification. This paper reports the effects of the different factors affecting HS-MS signal intensity in the quantification of the pollution of beach sands by hydrocarbons—the matrix effect, signal instability over time and nature of the different pollutants present in the polluted sands—and proposes possible solutions. Signal instability was solved by using a multiplicative calibration transfer algorithm. A three-factor Box–Behnken experimental design was used to study the matrix effect, mainly as regards the moisture of the samples, and the results are discussed.

Keywords: Headspace mass spectrometry; Hydrocarbon pollution; Quantification

Rapid voltammetric determination of nitroaromatic explosives at electrochemically activated carbon-fibre electrodes by Lourdes Agüí; Denis Vega-Montenegro; Paloma Yáñez-Sedeño; José M. Pingarrón (pp. 381-387).

The electrochemical behaviour of some nitroaromatic explosives (2,4,6-trinitrotoluene, TNT; 2,6-dinitrotoluene, 2,6-DNT; 2-nitrotoluene, 2-NT; 2-amino-4,6-dinitrotoluene, 2-A-4,6-DNT; 3,5-dinitroaniline, 3,5-DNA; and nitrobenzene, NB) at electrochemically activated carbon-fibre microelectrodes is reported. Electrochemical activation of such electrode material by repeated square-wave (SW) voltammetric scans between 0.0 and +2.6 V versus Ag/AgCl, produced a dramatic increase in the cathodic response from these compounds. This is attributed to the increase of the carbon-fibre surface area, because of its fracture, and the appearance of deep fissures along the main fibre axis into which the nitroaromatic compounds penetrate. Based on the important contribution of adsorption and/or thin layer electrolysis to the total voltammetric response, a SW voltammetric method for rapid detection of nitroaromatic explosives was developed. No interference was found from compounds such as hydrazine, phenolic compounds, carbamates, triazines or surfactants. The limits of detection obtained are approximately 0.03 μg mL⁻¹ for all the nitroaromatic compounds tested. The method was applied for the determination of TNT in water and soil spiked samples; recoveries were higher than 95% in all cases.

Keywords: Nitroaromatic explosives; Activated carbon fibre; Square-wave voltammetry

Residual aqueous ozone determination by gas diffusion reverse flow injection analysis by M. Baeza; J. Alonso; J. Bartrolí (pp. 388-395).

A novel system based on reverse flow injection analysis with a gaseous diffusion step (GD-r-FIA) has been developed for the analysis of ozone. It includes an automatic microburet injection system. The ozone diffuses through a microporous membrane of polyvinylidene difluoride (PVDF) from the donor stream to the acceptor stream containing nitrite ions. The nitrite concentration in the acceptor solution decreases due to the ozone reduction reaction. In this way, a simple indirect measurement of the ozone concentration can be performed using the Griess–Ilosvay reaction for the nitrite ion. This correlates with the decrease in absorbance of the azoic dye formed with the ozone concentration in the donor stream. The system has been optimised by investigating the effect of the nitrite concentration in the acceptor stream on the diffusion flow. The optimum nitrite concentration was set at 0.250 ppm with a flow rate of 1.5 ml/min. The efficiency of the ozone diffusion through the membrane was only 4.4%. This affects the average sensitivity, which is low (0.0092±0.0012 AU/ppm), although the detection limit is similar to that obtained with other reported methods (0.03 ppm). The main advantage of the system reported here is that it has a linear range that is an order of magnitude broader than those observed for other GD-FIA systems. This is especially useful for continuous monitoring systems, since the residual ozone concentration is normally between 0.05 and 5.0 ppm. Additionally, using the reverse flow injection analysis (FIA) technique minimises chemical consumption and residue generation. Finally, the stability of the ozone solution and the repeatability and reproducibility of the method have been studied.

Keywords: r-FIA; Ion nitrite; Automatic microburet; Adaptative analysis; GD; Ozone

A novel dynamic approach for automatic microsampling and continuous monitoring of metal ion release from soils exploiting a dedicated flow-through microdialyser by Manuel Miró; Modupe Jimoh; Wolfgang Frenzel (pp. 396-404).

In this paper, a novel concept is presented for automatic microsampling and continuous monitoring of metal ions in soils with minimum disturbance of the sampling site. It involves a hollow-fiber microdialyser that is implanted in the soil body as a miniaturized sensing device. The idea behind microdialysis in this application is to mimic the function of a passive sampler to predict the actual, rather than potential, mobility and bioavailability of metal traces. Although almost quantitative dialysis recoveries were obtained for lead (≥ 98%) from aqueous model solutions with sufficiently long capillaries (l ≥30 mm, 200 μm i.d.) at perfusion rates of 2.0 μL min⁻¹, the resistance of an inert soil matrix was found to reduce metal uptake by 30%. Preliminary investigation of the potential of the microdialysis analyser for risk assessment of soil pollution, and for metal partitioning studies, were performed by implanting the dedicated probe in a laboratory-made soil column and hyphenating it with electrothermal atomic absorption spectrometry (ETAAS), so that minute, well-defined volumes of clean microdialysates were injected on-line into the graphite furnace. A noteworthy feature of the implanted microdialysis-based device is the capability to follow the kinetics of metal release under simulated natural scenarios or anthropogenic actions. An ancillary flow set-up was arranged in such a way that a continuous flow of leaching solution — mild extractant (10⁻² mol L⁻¹ CaCl₂), acidic solution (10⁻³ mol L⁻¹ HNO₃), or chelating agent (10⁻⁴ or 10⁻² mol L⁻¹ EDTA) — was maintained through the soil body, while the concentration trends of inorganic (un-bound) metal species at the soil-liquid interface could be monitored at near real-time. Hence, relevant qualitative and quantitative information about the various mobile fractions is obtained, and metal-soil phase associations can also be elucidated. Finally, stimulus-response schemes adapted from neurochemical applications and pharmacokinetic studies are to be extended to soil research as an alternative means of local monitoring of extraction processes after induction of a chemical change in the outer boundary of the permselective dialysis membrane.

Keywords: Microdialysis; Metal ions; Soil; Continuous monitoring; Automated sampling

Evolution of ochratoxin A content from must to wine in Port Wine microvinification by N. Ratola; E. Abade; T. Simões; A. Venâncio; A. Alves (pp. 405-411).

To study the evolution of ochratoxin A (OTA) content from must to wine during the making of Port Wine, grapes from the five most common varieties of Port Wine were harvested and combined in equal percentages in order to perform microvinifications. Three sets of assays were studied: a blank (A), where the most common Port Wine-making process was used; in the second (B), a solution of OTA was added to the initial must; in the third (C), the grapes were aspersed with an inoculating solution of OTA-producing fungi. Samples were collected, in duplicate, on four different occasions throughout the process. The influence of the addition of SO₂ to the must was also assessed in each set. The quantification of OTA was based on the standard reference method for wines (European Standard prEN 14133), which includes clean-up via immunoaffinity columns and HPLC with fluorescence detection. The limits of detection were 0.076 μg/l for wine and 0.114 μg/l for must. The method was validated by assessing the precision, accuracy and by obtaining an estimate of the global uncertainty. Overall, the levels of OTA observed during the vinifications dropped by up to 92%, and no grapes used in this work were contaminated naturally.

Keywords: Ochratoxin A; Microvinification; Must; Port Wine; HPLC

Orthogonal signal correction applied to the classification of wine and molasses vinegar samples by near-infrared spectroscopy. Feasibility study for the detection and quantification of adulterated vinegar samples by María-José Sáiz-Abajo; José-María González-Sáiz; Consuelo Pizarro (pp. 412-420).

The most common fraudulent practice in the vinegar industry is the addition of alcohol of different origins to the base wine used to produce wine vinegar with the objective of reducing manufacturing costs. The mixture is then sold commercially as genuine wine vinegar, thus constituting a fraud to consumers and an unfair practice with respect to the rest of the vinegar sector. A method based on near-infrared spectroscopy has been developed to discriminate between white wine vinegar and alcohol or molasses vinegar. Orthogonal signal correction (OSC) was applied to a set of 96 vinegar NIR spectra from both original and artificial blends made in the laboratory, to remove information unrelated to a specific response. The specific response used to correct the spectra was the extent of adulteration of the vinegar samples. Both raw and corrected NIR spectra were used to develop separate classification models using the potential functions method as a class-modeling technique. The previous models were compared to evaluate the suitability of near-infrared spectroscopy as a rapid method for discrimination between vinegar origin. The transformation of vinegar NIR spectra by means of an orthogonal signal-correction method resulted in notable improvement of the specificity of the constructed classification models. The same orthogonal correction approach was also used to perform a calibration model able to detect and quantify the amount of exogenous alcohol added to the commercial product. This regression model can be used to quantify the extent of adulteration of new vinegar samples.

Keywords: Fraud detection; Wine vinegar; Molasses vinegar; NIR spectroscopy; Orthogonal signal correction; Potential functions

Analysis of organic acids in wines by Fourier-transform infrared spectroscopy by José Luís Moreira; Lúcia Santos (pp. 421-425).

Fourier-transform infrared (FTIR) spectroscopy has been a major point of development in many wine laboratories in recent years. It enables almost instant analysis of several properties of wine, usually with very good precision and accurate results. Nevertheless, validation procedures should not be forgotten and should be fully performed. Recovery experiments were performed by spiking wine samples with different amounts of organic acids (tartaric, malic, lactic, acetic and citric—the most prominent in wines). After FTIR analysis of the total acidity and of each organic acid concentration, recoveries were calculated. For total acidity recovery results were, in general, good and very close to 100% (64–111%). On the other hand, for individual organic acid concentrations, the recovery results were lower than 100% (11–73%) for all spiking additions. These results could be explained by spectroscopic interferences between the organic acids. Because they have similar infrared spectra, it is not easy to distinguish between them and, therefore, to achieve accurate calibration. When total acidity, with a different infrared spectrum from the other abundant compounds in the wine, was taken as a single property the recovery results were acceptable.

Keywords: Wine; Analysis; FTIR; Spectrometry; Interferences; Organic acids

Assessment of the essential element and heavy metal content of edible fish muscle by M. L. Carvalho; S. Santiago; M. L. Nunes (pp. 426-432).

The aim of this work was to determine the concentrations of some essential and toxic elements in the muscle of ten species of commercial fish consumed in Portugal. We combined two different techniques for determination of the elements—energy-dispersive X-ray fluorescence (EDXRF) was used to quantify K, Ca, Fe, Zn, Se, Rb, and Sr and flame atomic-absorption spectrometry for analysis of Cr, Ni, Cu, Cd, Hg, and Pb. The latter technique was used because of its higher sensitivity, because these elements were not detected by EDXRF. The results obtained show a similar pattern for the trace elements. K and Ca are present at the highest concentrations in all the samples studied, from 0.6–1.3% and from 0.04–0.08%, respectively, followed by Zn, Fe, Sr, Se, and Rb. Sr is present at higher concentrations than Rb in all the species studied except meagre. Concentrations of the elements in octopus do not follow this pattern—Fe is present at a higher concentration than Zn. Low concentrations of Cr (0.66–1.5 μg g⁻¹), Ni (0.11–0.24 μg g⁻¹), Cd (0.01–0.08 μg g⁻¹), Hg (0.49–2.74 μg g⁻¹), and Pb (0.02–0.06 μg g⁻¹) were observed in all the samples analysed. The concentration of Hg was highest in Helicolenus dactylopterus—5.4 μg g⁻¹ in one sample.

Keywords: Fish; Toxic elements; Flame atomic absorption spectrometry (FAAS); Energy-dispersive X-ray fluorescence (EDXRF); Biomonitoring

Determination of macrolide antibiotics in porcine and bovine urine by high-performance liquid chromatography coupled to coulometric detection by María José González de la Huebra; Ursula Vincent; Guy Bordin; Adela Rosa Rodríguez (pp. 433-439).

A high-performance liquid chromatography method coupled to coulometric detection has been applied for the determination, in a single run, of up to eight macrolide antibiotics (erythromycin [ERY], tylosin [TYL], tilmicosin [TILM], spiramycin 2 [SPI 2], spiramycin 3 [SPI 3], josamycin [JOS], kitasamycin [KIT], and rosamicin [ROS]) in spiked porcine and bovine urine. Quantification was performed using matrix-matched calibration with roxithromycin (ROX) as the internal standard. The detection limits for each drug were below 3.5 ng injected (equivalent to an initial concentration below 0.07 mg L⁻¹) for porcine urine and below 5 ng injected (equivalent to an initial concentration below 0.10 mg L⁻¹) for bovine urine. Recoveries from urine samples spiked at three different concentrations within the linear range were not significantly dependent on concentration. The entire procedure provides average macrolide recoveries ranging from 69.7 to 96.6% for bovine urine and from 75.5 and 96.1% for porcine urine.

Keywords: Macrolide antibiotics; Multiresidue method; Coulometric detection; High-performance liquid chromatography; Porcine urine; Bovine urine

Determination of ageing time of spirits in oak barrels using a headspace–mass spectrometry (HS-MS) electronic nose system and multivariate calibration by M Pilar Martí; Jorge Pino; Ricard Boqué; Olga Busto; Josep Guasch (pp. 440-443).

The aromatic composition of sugar cane spirits and, in general, of alcoholic beverages, is mainly influenced by the ageing process in wood barrels. There are several factors that affect the quality of the final aged product, but the time of the storage in the barrel is perhaps the most important one. Ageing time must therefore be controlled in order to detect counterfeits; however, this parameter is very difficult to control and, at present, there is no analytical method available to determine it. We propose a quantitative method for determining the ageing time of sugar cane spirits in oak barrels by using an electronic nose based on coupling directly a headspace sampler to a mass spectrometer (HS-MS), and multivariate calibration. The method developed is simple and provides, in 5 min, the ageing time of spirits with an accuracy of about 1 month.

Keywords: Electronic nose; HS-MS; Alcoholic beverages; Multivariate calibration; Ageing

Column preconcentration of gold by adsorbing AuCl₄⁻ onto methyltrioctyl ammonium chloride–naphthalene and subsequent atomic absorption spectrometric determination by M. Behpour; A. M. Attaran; S. M. Ghoreishi; N. Soltani (pp. 444-447).

A sensitive, selective and simple preconcentration method for ultra-trace gold determination has been developed that uses naphthalene–methyltrioctyl ammonium chloride (Aliquat 336s) as an adsorbent. Gold, in the form of AuCl₄⁻, was retained by the adsorbent in the column at a flow rate of 1 ml min⁻¹. After filtration, the solid mass consisting of the gold complex and naphthalene was dissolved out of the column with 5 ml of N,N-dimethylformamide (DMF), and the metal was then determined by atomic absorption spectrometry. In the initial solution, the calibration graph of absorbance versus gold concentration was found to be linear in the range 0.5–150 ng ml⁻¹ Au(III) with r=0.997 (n =9), and the 3 s detection limit was 0.428 ng ml⁻¹. The relative standard deviation for eight replicate measurements of 20 μg of gold was 2.14%. Preconcentration factors of 390 and 650 were achieved using 5 ml and 3 ml of DMF, respectively. The proposed method was successfully applied to the determination of gold in wastewater, processed pool water, slurry pool water, and raw well-water from the Moteh gold mine, and synthetic samples.

Keywords: Gold; Column preconcentration; Atomic absorption; Waste water

Improving the accuracy of carbon-to-hydrogen ratio determination for P, N, S, O, Cl, and Br-containing organic compounds using atomic emission detection by Elena S Chernetsova; Alexander I Revelsky; Dupont Durst; Tim G Sobolevsky; Igor A Revelsky (pp. 448-451).

The objective of this work was to investigate the dependence of atomic emission detector C and H response on microwave-induced plasma conditions and to improve the accuracy of carbon-to-hydrogen ratio determination for trialkylphosphates, herbicides, chlorophenols, and sulfur-containing organic compounds. Compounds which differed structurally from the analytes were used as reference compounds. It was found that when the oxygen concentration in the helium was the maximum for the instrument (9%) relative errors in carbon-to-hydrogen ratio determination were 3–8%, irrespective of analyte and reference compound structure, whereas when working in the mode of operation recommended by the manufacturer of the instrument (1.5% oxygen in helium) the respective errors were 10–20% or higher. This improvement in the accuracy of carbon-to-hydrogen ratio determination was accompanied by a factor of ten decrease in sensitivity.

Keywords: GC–AED; Carbon-to-hydrogen ratio determination; Trialkylphosphates; Herbicides; Chlorinated compounds; Brominated compounds; Sulfur-containing compounds

A catalytic multi-pumping flow system for the chemiluminometric determination of metformin by Karine L. Marques; João L. M. Santos; José L. F. C. Lima (pp. 452-457).

A multi-pumping flow system for the chemiluminometric determination of the hypoglycaemic drug metformin was implemented. The developed methodology was based on the metformin-induced inhibition (metformin acts as a Cu(II) scavenger) of the catalytic effect of Cu(II) ions on the chemiluminescent reaction between luminol and hydrogen peroxide. The flow manifold configuration was based on the utilisation of multiple solenoid-actuated micro-pumps that were simultaneously accountable for sample/reagent introduction and reaction zone formation/propulsion, thus resulting in a fully automated, simple and highly selective multi-pumping flow system. A versatile sample manipulation allowed the establishment of distinct sampling strategies with low reagent consumption. The characteristic pulsed flow ensured an effective sample/reagent mixing leading to a better and faster reaction zone homogenisation and thus improved analytical signals. Linear calibration plots were obtained for metformin hydrochloride concentrations ranging from 5 to 15 mg L⁻¹ with a relative standard deviation lower than 2.0% (n=5). Detection limit was 0.94 mg L⁻¹, and the sampling rate was about 95 determinations per hour. The developed methodology was applied to the analysis of pharmaceutical formulations and the obtained results were in agreement with those furnished by the reference method with relative percentage deviations of lower than 1.5%.

Keywords: Multi-pumping; Pulsed flow; Chemiluminescence; Metformin; Luminol; Copper

Use of near-infrared reflectance spectroscopy in predicting nitrogen, phosphorus and calcium contents in heterogeneous woody plant species by C. Petisco; B. García-Criado; B. R. Vázquez de Aldana; I. Zabalgogeazcoa; S. Mediavilla; A. García-Ciudad (pp. 458-465).

Near-infrared reflectance spectroscopy was applied to determine nitrogen (N), phosphorus (P) and calcium (Ca) content in leaf samples of 18 woody species. A total of 183 samples from mountain, riparian and dry areas from the Central–Western Iberian Peninsula were collected for this purpose. The wide intervals of variation observed in nutrient concentrations (6.6–45.0 g kg⁻¹ for N, 0.24–2.97 g kg⁻¹ for P, and 1.00–20.06 g kg⁻¹ for Ca) were due to the great heterogeneity of the samples. To develop calibration equations, multiple linear regression, and partial least-squares regression (PLSR) were used. In both cases, three mathematical transformations of the data were applied: log1/R and first and second derivatives. The best calibration statistics were obtained using PLSR and derivative transformations (second derivative for N and first derivative for P and Ca). The following coefficients of multiple determination (R²) and standard errors of cross validation were obtained: 0.99 and 0.93 for N, 0.94 and 0.15 for P, and 0.95 and 0.88 for Ca. In the external validation the standard errors of prediction obtained were 0.76 (N), 0.11 (P) and 0.60 (Ca).

Keywords: Near-infrared reflectance spectroscopy (NIRS); Chemical composition; Woody plant species

Application of ICP-OES to the determination of CuIn_1−xGa_xSe₂ thin films used as absorber materials in solar cell devices by Rodolfo Fernández-Martínez; Raquel Caballero; Cecilia Guillén; María Teresa Gutiérrez; María Isabel Rucandio (pp. 466-470).

CuIn_1−xGa_xSe₂ [CIGS; x=Ga/(In+Ga)] thin films are among of the best candidates as absorber materials for solar cell applications. The material quality and main properties of the polycrystalline absorber layer are critically influenced by deviations in the stoichiometry, particularly in the Cu/(In+Ga) atomic ratio. In this work a simple, sensitive and accurate method has been developed for the quantitative determination of these thin films by inductively coupled plasma optical emission spectrometry (ICP-OES). The proposed method involves an acid digestion of the samples to achieve the complete solubilization of CIGS, followed by the analytical determination by ICP-OES. A digestion procedure with 50% HNO₃ alone or in the presence of 10% HCl was performed to dissolve those thin films deposited on glass or Mo-coated glass substrates, respectively. Two analytical lines were selected for each element (Cu 324.754 and 327.396 nm, Ga 294.364 and 417.206 nm, In 303.936 and 325.609 nm, Se 196.090 and 203.985 nm, and Mo 202.030 and 379.825 nm) and a study of spectral interferences was performed which showed them to be suitable, since they offered a high sensitivity and no significant inter-element interferences were detected. Detection limits for all elements at the selected lines were found to be appropriate for this kind of application, and the relative standard deviations were lower than 1.5% for all elements with the exception of Se (about 5%). The Cu/(In+Ga) atomic ratios obtained from the application of this method to CIGS thin films were consistent with the study of the structural and morphological properties by X-ray diffraction (XRD) and scanning electron microscopy (SEM).

Keywords: ICP-OES; Solar cell applications; CuIn_1−xGa_xSe₂ thin films; Inter-element interferences

Simultaneous determination of phenolic compounds by means of an automated voltammetric “electronic tongue” by A. Gutés; A. B. Ibáñez; F. Céspedes; Salvador Alegret; M. del Valle (pp. 471-476).

This contribution describes the simultaneous determination of three phenolic compounds, o-cresol, p-chlorophenol and 4-chloro-3-methylphenol, using direct oxidation and amperometric detection coupled by signal deconvolution, accomplished via chemometric methods. Direct oxidation of phenolic compounds is performed at the surface of an epoxy-graphite transducer, by linear scan voltammetry. Due to strong signal overlapping, artificial neural networks (ANNs) were used during data treatment, in a combination of chemometrics and electrochemical sensors known as an “electronic tongue”. To calibrate this system properly, a total of 80 mixed samples were prepared automatically by employing a sequential injection analysis (SIA) system designed to automatically generate the information needed to train the network. The phenolic compound concentration varied from 1 to 70 μM for o-cresol, from 0.5 μM to 140 μM for p-chlorophenol and from 1 μM to 100 μM for 4-chloro-3-methylphenol. A good prediction capability was obtained, with correlation coefficients >0.964 when the obtained values were compared with those expected for a set of 24 external test samples not used for training. The results presented here indicate that this technique is a simple and robust analytical method of environmental interest.

Keywords: Phenols; Voltammetry; Artificial neural networks; “Electronic tongue”

Determination of ametryn in soils via microwave-assisted solvent extraction coupled to anodic stripping voltammetry with a gold ultramicroelectrode by Oriza Tavares; Simone Morais; Paula Paíga; Cristina Delerue-Matos (pp. 477-484).

An extraction-anodic adsorptive stripping voltammetric procedure using microwave-assisted solvent extraction and a gold ultramicroelectrode was developed for determining the pesticide ametryn in soil samples. The method is based on the use of acetonitrile as extraction solvent and on controlled adsorptive accumulation of the herbicide at the potential of 0.50 V (vs. Ag/AgCl) in the presence of Britton-Robinson buffer (pH 3.3). Soil sample extracts were analysed directly after drying and redissolution with the supporting electrolyte but without other pre-treatment. The limit of detection obtained for a 10 s collection time was 0.021 μg g⁻¹. Recovery experiments for the global procedure, at the 0.500 μg g⁻¹ level, gave satisfactory mean and standard deviation results which were comparable to those obtained by HPLC with UV detection.

Keywords: Ametryn; Gold ultramicroelectrode; Stripping voltammetry; Spiked soil samples; Microwave-assisted solvent extraction

Comparative study of atomic fluorescence spectroscopy and inductively coupled plasma mass spectrometry for mercury and arsenic multispeciation by José Luis Gómez-Ariza; Fernando Lorenzo; Tamara García-Barrera (pp. 485-492).

Mercury and arsenic are two elements of undoubted importance owing to their toxic character. Although speciation of these elements has been developed separately, in this work for the first time the speciation of As and Hg using two atomic fluorescence detectors in a sequential ensemble is presented. A coupling based on the combination of high-performance liquid chromatography (where mercury and arsenic species are separated) and two atomic fluorescence detectors in series, with several online treatments, including photooxidation (UV) and hydride generation, has allowed the determination of mercury and arsenic compounds simultaneously. The detection limits for this device were 16, 3, 17, 12 and 8 ng mL⁻¹ for As^III, monomethylarsinic acid, As^V, Hg²⁺ and methylmercury, respectively. This coupling was compared with an analogous one based on inductively coupled plasma–mass spectrometry (ICP-MS) detection, with detection limits of 0.7, 0.5, 0.8, 0.9 and 1.1 ng mL⁻¹, respectively. Multispeciation based on ICP-MS exhibits better sensitivity than the coupling based on tandem atomic fluorescence, but this second device is a very robust system and exhibits obvious advantages related to the low cost of acquisition and maintenance, as well as easy handling, which makes it a suitable system for routine laboratories.

Keywords: Mercury; Arsenic; Inductively coupled plasma mass spectrometry; Atomic fluorescence spectroscopy; Speciation; Multielemental speciation

Separation of biomolecules by μ-high-performance anion-exchange chromatography using a tentacle-like stationary phase by Nicola Dawn Marlin; Norman William Smith (pp. 493-497).

A variety of biomolecules and their variants, which have previously been problematic to separate, have been analysed using a novel anion-exchange resin based on a non-porous polystyrene polymeric support with a hydrophilic coating and grafted tentacular quaternary ammonium functional groups. The hydrophilic coating results in minimal interaction between the support and the biomolecule, while the highly flexible tentacular-like anion-exchange groups increase the ionic interaction potential and act as an umbrella to hold the proteins away from the surface. Because of the removal of silanophilic interactions, minimisation of hydrophobic interactions, and the highly flexible nature of the tentacle-like ion exchangers, ionic interactions can therefore dominate the separation. As such this phase is highly suited to the separation of highly charged biomolecules and their variants. This polymeric strong anion-exchange (SAX) support was packed into a fused-silica capillary column and, using a salt concentration gradient, various recombinant proteins were analysed by μ-HPLC resulting in baseline resolution.

Keywords: Anion exchange; Bioanalytical; MicroLC; Proteins

Determination of ethyl carbamate in alcoholic beverages: an interlaboratory study to compare HPLC-FLD with GC-MS methods by Susana de Melo Abreu; Arminda Alves; Beatriz Oliveira; Paulo Herbert (pp. 498-503).

An international interlaboratory study on the determination of ethyl carbamate in alcoholic beverages by a new HPLC-FLD and by the official GC-MS methods is presented. The aim of this study was to improve the knowledge about precision and accuracy parameters of the new method and to compare the performance of both HPLC and GC methods. Five different samples representing table wines, fortified wines (red and white), distilled spirits, and wine spirits were available for analysis by each participant. Despite the low number of participants (6), the results obtained by the laboratories using the HPLC-FLD method are comparable to those obtained by GC-MS methods. The present study emphasizes the possibility to use, as routine, a much simpler analytical method than the current reference method by GC-MS for ethyl carbamate determination in alcoholic beverages.

Keywords: Ethyl carbamate; Alcoholic beverages; Interlaboratory study; GC-MS; HPLC-FLD

The selectivity in MEKC of pseudo-stationary phases based on polyelectrolyte complexes: I. composition of the complex by Alexey V. Shpak; Andrey V. Pirogov; Oleg A. Shpigun (pp. 504-512).

Polyelectrolyte–surfactant complexes (PSC) of polycarboxylic acids with alkyl-trimethylammonium salts look very promising as a new type of pseudo-stationary phase in micellar electrokinetic chromatography. PSC produce an intramolecular micellar phase, and the morphology of the micelles is significantly different from that of the corresponding “typical” surfactant micelles. Pseudo-stationary phases based on PSC have unique selectivity. In this paper, the effect of the composition (φ) of the PSC of polyacrylic acid (PAA) M_W 130,000 with dodecyltrimethylammonium bromide (DTAB) and of the PSC of PAA M_W 450,000 with DTAB on the separation of DNS–amino acids and phenol derivatives in these systems was investigated. Relative retention and relative selectivity were used to describe the electrophoretic behavior of the amino acids and phenol derivatives. The main advantage of PSC pseudo-phases is that the nature and the structure of micelle-like units, and hence the selectivity of electrophoretic separation, could easily be modified by changing the composition of the complex.

Keywords: Pseudo-stationary phases; Polyelectrolyte complexes; MEKC; Polyacrylic acid; Selectivity

Use of 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide immobilized on silica gel for automated preconcentration and selective determination of antimony(III) by flow-injection electrothermal atomic absorption spectrometry by C. Bosch Ojeda; F. Sánchez Rojas; J. M. Cano Pavón; L. Terrer Martín (pp. 513-518).

Selective sorption of Sb(III) on a microcolumn packed with 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide immobilized on silica gel (DPTH-gel) has been used for determination of Sb(III). A flow-injection system comprising a microcolumn connected to the tip of the autosampler was used for preconcentration. The sorbed antimony was eluted with nitric acid directly into the graphite furnace and determined by AAS. The detection limit for antimony under the optimum conditions was 0.3 ng mL⁻¹. This procedure was used for determination of antimony in natural water, soil, vegetation, and a certified sample of a city waste incineration ash (BCR 176).

Keywords: Antimony; Electrothermal atomic absorption spectrometry; Preconcentration; Microcolumn; Flow injection

Multiresidue analysis of phenylurea herbicides in environmental waters by capillary electrophoresis using electrochemical detection by M. Chicharro; E. Bermejo; A. Sánchez; A. Zapardiel; A. Fernandez-Gutierrez; D. Arraez (pp. 519-526).

A rapid multiresidue method has been developed for the analysis of seven phenylurea herbicides in the presence of two s-triazines in environmental waters. A simple end-column electrochemical detector was used in combination with a commercially-available capillary electrophoresis instrument with UV detection. The determination of phenylurea pesticides using micellar electrokinetic capillary chromatography with electrochemical detection represents the first such determination that has been reported. In both detection systems, linear ranges were obtained for the seven phenylurea herbicides at concentrations lower than 2.0×10⁻⁵ mol l⁻¹, in 0.020 mol l⁻¹ phosphoric acid at pH 7.0 and containing 0.020 mol l⁻¹ of sodium dodecylsulfate, in order to obtain selectivity in the additional separation by a micellar distribution process. Under these conditions a detection limit lower than 5.0×10⁻⁶ mol l⁻¹ (0.25 pmol of pesticide) was achieved for most of them. The pesticides were resolved in less than 30 min.

Keywords: Micellar electrokinetic capillary chromatography; Electrochemical detection; Phenylurea herbicides; Environmental waters

Rapid analysis of pyrethroids in whole urine by high-performance liquid chromatography using a monolithic column and off-line preconcentration in a restricted access material cartridge by M.E. León-González; M. Plaza-Arroyo; L.V. Pérez-Arribas; L.M. Polo-Díez (pp. 527-531).

A rapid high-performance liquid chromatography (HPLC) method using a monolithic column with UV detection at 238 nm was developed for the determination of fenpropathrin, betacyfluthrin, deltamethrin, and permethrin (cis and trans isomers) in whole urine. The method is based on the use of a monolithic chromatographic column and a restricted access material (RAM) cartridge for sample preparation. The mobile phase was water/acetonitrile (42:58 v/v), the flow rate was 3 mL min⁻¹, and chromatographic separation was carried out in 10 min. The separation of cis and trans isomers of permethrin was also possible under the above-mentioned conditions. Detection limits in reconstituted whole urine samples were between 0.9 μg L⁻¹ for betacyfluthrin and 4.4 μg L⁻¹ for fenpropathrin and trans-permethrin. Recoveries for urine samples spiked with different amounts of pyrethroids (between 19 μg L⁻¹ and 75 μg L⁻¹) were in the 70±6 to 90±7% range.

Keywords: Pyrethroid insecticides; Monolithic column; Restricted access material cartridge; Urine

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Analytical and Bioanalytical Chemistry (v.382, #2)

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Analytical and Bioanalytical Chemistry (v.382, #2)