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Analytica Chimica Acta (v.577, #1)

Contents (pp. v-vi).

Editorial Board (pp. co1).

Calendar of forthcoming meetings (pp. n1).

Contents (pp. v-vi).

Editorial Board (pp. co1).

Calendar of forthcoming meetings (pp. n1).

Chromatographic separation for domoic acid using a fragment imprinted polymer by Takuya Kubo; Makoto Nomachi; Koji Nemoto; Tomoharu Sano; Ken Hosoya; Nobuo Tanaka; Kunimitsu Kaya (pp. 1-7).

We prepared molecularly imprinted polymers for an amnesic shellfish poison, domoic acid. To prepare the polymer, we tested several commercial aromatic dicarboxylic compounds such as isomers of phthalic acid for templates of molecularly imprinted polymers. The highest selective recognition ability of the polymer for domoic acid in the tested compounds was found when o-phthalic acid was used as the template. The ability was due to the acidity of the carboxylic acids in the domoic acid and the similarity of the shape around the carboxylic acids of domoic acid and the templates. The effective chromatographic separation of domoic acid in the extract from blue mussels was achieved with a LC column packed with the fragment imprinted polymer using o-phthalic acid as the template. This polymer can be utilized for a clean up procedure of domoic acid in toxic shellfish.

Keywords: Molecularly imprinted polymer; Domoic acid; Selective separation; LC

Chromatographic separation for domoic acid using a fragment imprinted polymer by Takuya Kubo; Makoto Nomachi; Koji Nemoto; Tomoharu Sano; Ken Hosoya; Nobuo Tanaka; Kunimitsu Kaya (pp. 1-7).

Keywords: Molecularly imprinted polymer; Domoic acid; Selective separation; LC

Ultra-performance liquid chromatography–tandem mass spectrometry: A novel challenge in multiresidue pesticide analysis in food by Tomáš Kovalczuk; Martin Jech; Jan Poustka; Jana Hajšlová (pp. 8-17).

Potential of ultra-performance liquid chromatography (UPLC) separation strategy coupled with tandem (in space) mass spectrometric detection (MS/MS) in multiresidue pesticide analysis was critically assessed. Performance parameters such as number of theoretical plates, height of theoretical plate, peak symmetry and peak capacity were measured/calculated on the basis of data generated by analysis of apple extracts containing 17 (semi)polar pesticides representing various classes of active ingredients of widely used crop protective preparations. Ultra-performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) procedure provided improved chromatographic parameters resulting in significantly increased sample throughput including lower solvent consumption and lower limits of quantitation (LOQs) for most of target analytes compared to common method employing conventional high-performance liquid chromatography (HPLC) separation.

Keywords: Ultra-performance liquid chromatography; High-performance liquid chromatography; Tandem quadrupole mass spectrometry; Multiresidue; Pesticides; Food analysis

Method optimization for the determination of four mercury species by micro-liquid chromatography–inductively coupled plasma mass spectrometry coupling in environmental water samples by A. Castillo; A.F. Roig-Navarro; O.J. Pozo (pp. 18-25).

A method based on the coupling microHPLC–microneb-ICPMS has been developed for Hg(II), MeHg⁺, EtHg⁺ and PhHg⁺ species. Gradient elution using methanol andl-cysteine at pH 3.0 allowed the chromatographic separation of all species in less than 13min (total analysis time 15min). The direct coupling of microLC to ICPMS through a Micromist nebulizer permits the analysis of environmental water without sample pretreatment and derivatization steps. Nebulizer type, organic modifier and column length were the main parameters tested. The methanol content and pH of the mobile phase greatly affected the retention time and sensitivity of the method. Key factors to obtain high signal to noise ratio, at concentrations below 1μgL⁻¹, were found to be the nebulization step and traces of Hg present in the complexing agent. A detailed optimization of carrier and make up gas flow rates have enabled the nebulization of the methanol gradient elution with good mass transport efficiency, low organic solvent loading into the plasma and excellent precision.The performance of the microHPLC–microneb-ICPMS method developed was evaluated on a surface water sample filtered (0.22μm) and spiked with 0.5μgL⁻¹ (as Hg) of each species. Precision (R.S.D., n=6) for all species of Hg varied from 0.5 to 2.1%. Detection limit, defined as three times the standard deviation ( n=6), ranged from 8ngL⁻¹ for EtHg⁺ to 32ngL⁻¹ for PhHg⁺ and was noticeably lower than those reported in previous LC-based methods. Accuracy was suitable with recoveries ranging from 85 to 100% when tested at two levels (0.5 and 10μgL⁻¹) in groundwater samples. Recovery was matrix affected when water samples of high salinity (depurated wastewater and seawater) were used.

Keywords: Mercury speciation; Microbore column; Micro-liquid chromatography; Micronebulizer; Inductively coupled plasma mass spectrometry; Water

Simultaneous determination of naphthoquinone derivatives in Boraginaceous herbs by high-performance liquid chromatography by Yani Hu; Zhihong Jiang; Kelvin Sze-Yin Leung; Zhongzhen Zhao (pp. 26-31).

A high-performance liquid chromatographic method using diode-array detection (HPLC-DAD) has been developed for the simultaneous quantification of eight naphthoquinone derivatives namely shikonin, acetylshikonin, deoxyshikonin, β-acetoxyisovalerylshikonin, isobutylshikonin, β,β-dimethylacrylshikonin, 2-methyl- n-butyrylshikonin and isovalerylshikonin in nine species of the Boraginaceae family. These species, coming from different areas of China, are all used as interchangeable sourcing plants for the Chinese Materia Medica known as “Zicao�?, and are Arnebia euchroma (Royle) Johnston., A. guttata Bunge, Lithospermum erythrorhizon Sieb. et Zucc., Onosma paniculatum Bur. et Franch., O. exsertum Hemsl., O. confertum W.W. Smith, O. hookerii Clarke var. longiflorum Duthie, O. hookerii Clarke and O. waltonii Duthic. Quantification of the eight naphthoquinones in all the Zicao samples are reported and compared with each other. Furthermore, two positional isomers, 2-methyl- n-butyrylshikonin and isovalerylshikonin, were successfully separated and quantified for the first time in the present study. The results showed that, besides the three officially used species (namely, A. euchroma, A. guttata and L. erythrorhizon) that were listed in Chinese pharmacopoeia as interchangeable sourcing plants for Zicao, other six species of Onosma used by native peoples in Tibet and Yunnan Province also contain various types and considerable amounts of naphthoquinones and that O. waltonii contains the most. Therefore, these species of Onosma could be developed as new sources of naphthoquinones. The entire analytical procedure is reproducible and suitable for the quantification of naphthoquinones in all related Boraginaceous plants for quality assessment purposes.

Keywords: Boraginaceae; Arnebia; spp.; Lithospermum; spp.; Onosma; spp.; Naphthoquinone; Zicao

A high-performance liquid chromatographic method using diode-array detection (HPLC-DAD) has been developed for the simultaneous quantification of eight naphthoquinone derivatives namely shikonin, acetylshikonin, deoxyshikonin, β-acetoxyisovalerylshikonin, isobutylshikonin, β,β-dimethylacrylshikonin, 2-methyl- n-butyrylshikonin and isovalerylshikonin in nine species of the Boraginaceae family. These species, coming from different areas of China, are all used as interchangeable sourcing plants for the Chinese Materia Medica known as “Zicao”, and are Arnebia euchroma (Royle) Johnston., A. guttata Bunge, Lithospermum erythrorhizon Sieb. et Zucc., Onosma paniculatum Bur. et Franch., O. exsertum Hemsl., O. confertum W.W. Smith, O. hookerii Clarke var. longiflorum Duthie, O. hookerii Clarke and O. waltonii Duthic. Quantification of the eight naphthoquinones in all the Zicao samples are reported and compared with each other. Furthermore, two positional isomers, 2-methyl- n-butyrylshikonin and isovalerylshikonin, were successfully separated and quantified for the first time in the present study. The results showed that, besides the three officially used species (namely, A. euchroma, A. guttata and L. erythrorhizon) that were listed in Chinese pharmacopoeia as interchangeable sourcing plants for Zicao, other six species of Onosma used by native peoples in Tibet and Yunnan Province also contain various types and considerable amounts of naphthoquinones and that O. waltonii contains the most. Therefore, these species of Onosma could be developed as new sources of naphthoquinones. The entire analytical procedure is reproducible and suitable for the quantification of naphthoquinones in all related Boraginaceous plants for quality assessment purposes.

Keywords: Boraginaceae; Arnebia; spp.; Lithospermum; spp.; Onosma; spp.; Naphthoquinone; Zicao

Low pressure ion chromatography with a low cost paired emitter–detector diode based detector for the determination of alkaline earth metals in water samples by Leon Barron; Pavel N. Nesterenko; Dermot Diamond; Martina O’Toole; King Tong Lau; Brett Paull (pp. 32-37).

The use of a low pressure ion chromatograph based upon short (25mm×4.6mm) surfactant coated monolithic columns and a low cost paired emitter–detector diode (PEDD) based detector, for the determination of alkaline earth metals in aqueous matrices is presented. The system was applied to the separation of magnesium, calcium, strontium and barium in less than 7min using a 0.15M KCl mobile phase at pH 3, with post-column reaction detection at 570nm using o-cresolphthalein complexone. A comparison of the performance of the PEDD detector with a standard laboratory absorbance detector is shown, with limits of detection for magnesium and calcium using the low cost PEDD detector equal to 0.16 and 0.23mgL⁻¹, respectively. Finally, the developed system was used for the determination of calcium and magnesium in a commercial spring water sample.

Keywords: Low pressure ion chromatography; Alkaline earth metals; Post-column reaction; Paired emitter–detector diode detector

Approach for ochratoxin A fast screening in spices using clean-up tandem immunoassay columns with confirmation by high performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) by I.Yu. Goryacheva; S. De Saeger; M. Lobeau; S.A. Eremin; I. Barna-Vetró; C. Van Peteghem (pp. 38-45).

An approach for ochratoxin A (OTA) fast cost-effective screening based on clean-up tandem immunoassay columns was developed and optimized for OTA detection with a cut-off level of 10μgkg⁻¹ in spices. Two procedures were tested and applied for OTA detection. Column with bottom detection immunolayer was optimized for OTA determination in Capsicum ssp. spices. A modified clean-up tandem immunoassay procedure with top detection immunolayer was successfully applied for all tested spices. Its main advantages were decreasing of the number of analysis steps and quantity of antibody and also minimizing of matrix effects. The total duration of the extraction and analysis was about 40min for six samples. Chilli, red pepper, pili-pili, cayenne, paprika, nutmeg, ginger, white pepper and black pepper samples were analyzed for OTA contamination by the proposed clean-up tandem immunoassay procedures. Clean-up tandem immunoassay results were confirmed by HPLC–MS/MS with immunoaffinity column clean-up. Among 17 tested Capsicum ssp. spices, 6 samples (35%) contained OTA in a concentration exceeding the 10μgkg⁻¹ limit discussed by the European Commission. All tested nutmeg ( n=8), ginger ( n=5), white pepper ( n=7) and black pepper ( n=6) samples did not contain OTA above this action level.

Keywords: Ochratoxin A; Spices; Screening; Immunoassay; High performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS)

Validated high-performance thin-layer chromatography method for determination of trigonelline in herbal extract and pharmaceutical dosage form by Shruti Chopra; Farhan J. Ahmad; Roop K. Khar; Sanjay K. Motwani; Saiqa Mahdi; Zeenat Iqbal; Sushma Talegaonkar (pp. 46-51).

A new, simple, sensitive, selective, precise and robust high-performance thin-layer chromatographic (HPTLC) method for analysis of trigonelline was developed and validated for the determination of trigonelline in herbal extracts and in pharmaceutical dosage forms. Analysis of trigonelline was performed on TLC aluminium plates pre-coated with silica gel 60F-254 as the stationary phase. Linear ascending development was carried out in twin trough glass chamber saturated with mobile phase consisting of n-propanol-methanol-water (4:1:4, v/v/v) at room temperature (25±2°C). Camag TLC scanner III was used for spectrodensitometric scanning and analysis in absorbance mode at 269nm. The system was found to give compact spots for trigonelline ( R_f value of 0.46±0.02). The linear regression analysis data for the calibration plots showed good linear relationship with r²=0.9991±0.0002 in the concentration range 100–1200ng spot⁻¹ with respect to peak area. According to the International Conference on Harmonization (ICH) guidelines the method was validated for precision, recovery, robustness and ruggedness. The limits of detection and quantification were determined. The trigonelline content of herbal extracts quantified and estimated from the formulation was found to be well within limits (±5% of the labeled content of the formulations). Statistical analysis of the data showed that the method is reproducible and selective for the estimation of trigonelline.

Keywords: Trigonelline; High-performance thin layer chromatography; Method validation; Quantitative analysis; Herbal extract; Gels

Optimisation of derivatisation for the analysis of estrogenic compounds in water by solid-phase extraction gas chromatography–mass spectrometry by Z.L. Zhang; A. Hibberd; J.L. Zhou (pp. 52-61).

An optimisation of derivatisation methods for the simultaneous determination of endocrine disrupting chemicals (EDCs) in water by solid-phase extraction (SPE) gas chromatography–mass spectrometry (GC–MS) was developed in this study. Seven highly potent EDCs including 17β-estradiol (E2), estrone (E1), 16α-hydroxyestrone, 17α-ethynylestradiol (EE2), bisphenol A, 4-nonylphenol and 4- tert-octylphenol were selected as the target compounds. The SPE technique, followed by the derivatisation with N, O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) was used for the extraction recoveries of compounds from water and effluent samples. The stability of the silylation derivatives under different reaction conditions was investigated. The combined use of BSTFA and pyridine as derivatisation reagents, together with the use of hexane as the final solvent, was preferred in order to generate more stable derivatives of EDCs. The relative response factor (RRF) of all derivatives except that of EE2 was stable 120h after derivatisation. The addition of pyridine as derivatisation reagent with BSTFA can prevent the conversion of EE2 to other products during the reaction. Several parameters that may affect the recovery of EDCs, such as the SPE flow rate, and water properties including aquatic colloid content and surfactant concentration were tested. The results showed that the flow rate (1–25mLmin⁻¹), colloid concentration (0–50mgL⁻¹) and surfactants concentration (0–10μgL⁻¹) did not cause significant decrease in the EDCs recovery.

Keywords: Endocrine disrupting chemicals; Solid-phase extraction; Steroids; Phenolic compounds; Gas chromatography–mass spectrometry

Optimisation of derivatisation for the analysis of estrogenic compounds in water by solid-phase extraction gas chromatography–mass spectrometry by Z.L. Zhang; A. Hibberd; J.L. Zhou (pp. 52-61).

Keywords: Endocrine disrupting chemicals; Solid-phase extraction; Steroids; Phenolic compounds; Gas chromatography–mass spectrometry

Simultaneous determination of preservatives in soft drinks, yogurts and sauces by a novel solid-phase extraction element and thermal desorption-gas chromatography by Lili Wang; Xiao Zhang; Yiping Wang; Wei Wang (pp. 62-67).

A novel solid-phase extraction element combined with thermal desorption-gas chromatography (TD-GC) using a pyrolysis-GC system was applied for the determination of the five preservatives – benzoic acid, sorbic acid, and methyl, ethyl and propyl esters of p-hydroxybenzoic acid – in soft drinks, yogurts and sauces. The extraction element is made of a titanium (Ti) tubing (30mm×1.2mm i.d.×1.6mm o.d.) coated with a chemically bonded layer of polydimethylsiloxane (PDMS) to a thickness of 500μm. A sample pH of 2.0, sample volume of 5ml, extraction time of 45min with addition of salt (15% m/v NaCl) and TD temperature from 40 to 280°C at a heating rate of 40°Cmin⁻¹ and maintained at 280°C for 9min, were selected as optimum extraction and desorption conditions. The linearity of the method was satisfactory over a concentration range of 2–1000mgL⁻¹ for benzoic acid and sorbic acid, 0.2–300mgL⁻¹ for methyl ester of p-hydroxybenzoic acid, and 0.02–300mgL⁻¹ for ethyl and propyl esters of p-hydroxybenzoic acid, and the correlation coefficients were higher than 0.997. The limit of detection ranged from 0.002 to 0.2mgL⁻¹. The potential of the proposed method was assessed by applying it to the determination of preservatives in real samples. The recoveries (92–106%) and precisions (R.S.D.s of 0.9–4.6% ( n=5)) of the method were examined by analyzing soft drink, yogurt and sauce samples spiked at levels of between 20 and 100mgL⁻¹. This simple, accurate and highly sensitive method may be used in the determination of the preservatives in various water-based food samples.

Keywords: Preservatives; Extraction method; Polydimethylsiloxane; Thermal desorption; Gas chromatography

Evaluation of the electrophoretic behaviour of opioid peptides by Victoria Sanz-Nebot; Fernando Benavente; Elena Hernández; José Barbosa (pp. 68-76).

A general equation established in a previous study was used to model the electrophoretic mobility of a series of opioid peptides as a function of pH of the separation electrolyte. The concordance between the predicted and the experimental electrophoretic mobilities was excellent and the optimum pH for the separation of the modelled compounds could be predicted from a limited amount of experimental data. The equations were also useful for the accurate determination of the ionization constants of the polyprotic analytes. It was also demonstrated that if ionization constant values are known, the CE separations of the studied peptides can easily be predicted taking into account the classical semiempirical relationships between electrophoretic mobility and charge-to-mass ratio ( m_e versus q/ M^α). The separations simulated considering the accurate charge-to-mass ratios of each peptide at a certain pH value were in good agreement with the experimental results.Once an optimum separation pH value and a running buffer compatible with electrospray mass spectrometry (ESI) detection were selected, a method for the separation and characterization of this series of analytes by capillary electrophoresis-electrospray ionization mass spectrometry (CE-ESI-MS) was established using a commercial sheath–flow interface. Method validation was performed in order to prove the suitability of the proposed method for quantitative analysis. Thus, quality parameters, such as repeatability, reproducibility, limits of detection and linearity were determined.

Keywords: Neuropeptides; Capillary electrophoresis; Migration prediction; Ionization constants; Mass spectrometry

Evaluation of the electrophoretic behaviour of opioid peptides by Victoria Sanz-Nebot; Fernando Benavente; Elena Hernández; José Barbosa (pp. 68-76).

Keywords: Neuropeptides; Capillary electrophoresis; Migration prediction; Ionization constants; Mass spectrometry

A novel fluorescent array for mercury (II) ion in aqueous solution with functionalized cadmium selenide nanoclusters by Jinlong Chen; YingChun Gao; ZhiBing Xu; GenHua Wu; YouCun Chen; ChangQing Zhu (pp. 77-84).

Mono-disperse CdSe nanoclusters have been prepared facilely and functionalized withl-cysteine through two steps by using safe and low cost substances. They are water-soluble and biocompatible. Especially these functionalized quantum dots can be stably soluble in water more than for 30 days, and the intensity of fluorescence and absorbance was decreased less than 15% of fresh prepared CdSe colloids. These functionalized CdSe QDs exhibited strong specific affinity for mercury (II) through QDs interface functional groups. Based on the quenching of fluorescence signals of functionalized CdSe QDs at 530nm and no obvious wavelength shift or no new emission band in present of Hg (II) at pH 7.75 of phosphate buffer solution, a simple, rapid and specific array for Hg (II) was proposed. In comparison with conventional organic fluorophores, these nanoparticles are brighter, more stable against photobleaching, and do not suffer from blinking. Under optimum conditions, the response of linearly proportional to the concentration of Hg (II) between 0 and 2.0×10⁻⁶molL⁻¹, and the limit of detection is 6.0×10⁻⁹molL⁻¹. The relative standard deviation of six replicate measurements is 1.8% for 1.0×10⁻⁷molL⁻¹ Hg (II). The mechanism of reaction is also discussed. The proposed method was successfully applied for Hg (II) detection in four real samples with a satisfactory result that was obtained by cold vapor atomic fluorescence spectrometry (CV-AFS).

Keywords: Cadmium selenide nanoclusters; Fluorescence; Mercury (II)

Sulfonated poly(ether ether ketone) as an alternative charged material to poly(vinyl chloride) in the design of ion-selective electrodes by Anna González-Bellavista; Jorge Macanás; Maria Muñoz; Esteve Fabregas (pp. 85-90).

To date, poly(vinyl chloride) (PVC) is the most used polymer in the design of ion selective electrode (ISE) membranes. This paper is focused on the use of sulfonated poly(ether ether ketone) (SPEEK) as an alternative material to PVC for the design of ISEs. SPEEK of the desired degree of sulfonation is synthesized from poly(ether ether ketone) (PEEK). An NH₄⁺-ISE has been chosen as a model electrode to study the efficiency of SPEEK as polymer matrix of the membrane. The material was evaluated in ionophore free ion exchanger membranes as well as in ion-selective electrodes membranes containing nonactine as ionophore. Analytical performance parameters of the prepared electrodes were evaluated. The electrodes show a slope between 50 and 60mVdec⁻¹ depending on both the calibration medium and the membrane composition. A linear range of response between 10⁻⁴ and 1.0M and a lifetime of 1–2 months were obtained. The interferences of cations such us Ca²⁺, Na⁺, Li⁺ and K⁺ over the prepared ISEs are studied as well. Although the plasticizer in the SPEEK based membrane matrix is not necessary, its presence improves the sensibility. This makes SPEEK a good potential choice over alternative membrane matrices reported in the literature and a promising platform for the establishment of membrane components.

Keywords: Sulfonated polyether ether ketone; Charged membrane; Ion-selective electrode; Ammonium

Organotin compounds: An ionophore system for fluoride ion recognition by Sudeshna Chandra; Aleš Růži�?ka; Petr Švec; Heinrich Lang (pp. 91-97).

Ion-selective properties were established for membrane electrodes prepared by using organotin compounds of type (L^CNRSnF₂)_n, (R= n-Bu (I),=Ph (II)) and (L^CNSnF₃)_n (III) (L^CN=C₆H₄(CH₂NMe₂)-2). Electrodes formulated with the optimized membranes containing the organotin compoundsI–III as ionophores and sodium tetraphenylborate (10–30%) exhibited high selectivity for fluoride over other anions. An electrode prepared with ionophoreII using dibutyl phthalate as the plasticizer and 15% sodium tetraphenylborate (NaTPB) as anion additive, possesses the best potentiometric response characteristics. It shows a detection limit of 7.9×10⁻⁷M with a slope of 62.7mVdecade⁻¹ of activity in buffer solutions of pH 5.5. The interference from other anions is suppressed under this optimized measurement conditions. An entirely non-Hofmeister selectivity sequence (F⁻>CH₃COO⁻>Cl⁻>I⁻∼Br⁻>ClO₄⁻>NO₂⁻>NO₃⁻>SCN⁻) with remarkable preference towards fluoride is obtained. The influence on the electrode performances by anion additive was studied, and the possible response mechanism was investigated by UV–vis spectra. The electrode has been used for direct determination of fluoride in drinking mineral water with satisfactory results.

Keywords: Organotin compounds; Fluoride selective electrode; Ionophores; Anion recognition

Organotin compounds: An ionophore system for fluoride ion recognition by Sudeshna Chandra; Aleš Růžička; Petr Švec; Heinrich Lang (pp. 91-97).

Keywords: Organotin compounds; Fluoride selective electrode; Ionophores; Anion recognition

Electrodeposited glucose oxidase/anionic clay for glucose biosensors design by Adriana Mignani; Erika Scavetta; Domenica Tonelli (pp. 98-106).

An amperometric glucose biosensor was developed using an anionic clay matrix (layered double hydroxide (LDH), Ni/Al–NO₃) for the immobilization of glucose oxidase (GOx). The biofilm was prepared by electrodeposition of the clay and GOx and subsequent cross-linking with glutaraldeyde. The Pt surface modified with the Ni/Al–NO₃ shows a much reduced noise, giving rise to a better signal to noise ratio for the currents relative to H₂O₂ oxidation, and a linear range for H₂O₂ determination wider than the one observed for bare Pt electrodes. Under the optimised operative conditions, the performances of the biosensor have been evaluated by measuring the steady-state currents (at +0.45V versus SCE) to increasing concentrations of glucose in “air saturated�? 0.1M phosphate buffer (pH 7.0). Both batch and flow injection modes were explored. The response to glucose was linear up to 8.0 and 12.0mM, and the sensitivities were 7.7±0.1 and 19.1±0.2mAM⁻¹cm⁻², respectively. The current response of the biosensors does not significantly change for 15 consecutive days in batch and for 10 days in flow, at least, if stored at 4°C in phosphate buffer, when not in use. The effects of interferants and applicability to fruit juices and soft drinks analysis of the biosensor were also investigated.

Keywords: Amperometric biosensor; Glucose oxidase; Layered double hydroxides; Electrodeposition; Interferants

Electrodeposited glucose oxidase/anionic clay for glucose biosensors design by Adriana Mignani; Erika Scavetta; Domenica Tonelli (pp. 98-106).

An amperometric glucose biosensor was developed using an anionic clay matrix (layered double hydroxide (LDH), Ni/Al–NO₃) for the immobilization of glucose oxidase (GOx). The biofilm was prepared by electrodeposition of the clay and GOx and subsequent cross-linking with glutaraldeyde. The Pt surface modified with the Ni/Al–NO₃ shows a much reduced noise, giving rise to a better signal to noise ratio for the currents relative to H₂O₂ oxidation, and a linear range for H₂O₂ determination wider than the one observed for bare Pt electrodes. Under the optimised operative conditions, the performances of the biosensor have been evaluated by measuring the steady-state currents (at +0.45V versus SCE) to increasing concentrations of glucose in “air saturated” 0.1M phosphate buffer (pH 7.0). Both batch and flow injection modes were explored. The response to glucose was linear up to 8.0 and 12.0mM, and the sensitivities were 7.7±0.1 and 19.1±0.2mAM⁻¹cm⁻², respectively. The current response of the biosensors does not significantly change for 15 consecutive days in batch and for 10 days in flow, at least, if stored at 4°C in phosphate buffer, when not in use. The effects of interferants and applicability to fruit juices and soft drinks analysis of the biosensor were also investigated.

Keywords: Amperometric biosensor; Glucose oxidase; Layered double hydroxides; Electrodeposition; Interferants

Flow injection chemiluminescence determination of naproxen based on KMnO₄–Na₂SO₃ reaction in neutral aqueous medium by Yinhuan Li; Jiuru Lu (pp. 107-110).

A simple, rapid and sensitive flow injection chemiluminescence (CL) method is described for the determination of naproxen. It was found that strong CL signal was generated when naproxen was mixed with KMnO₄ and Na₂SO₃ in neutral aqueous medium. Under the optimum experimental conditions, the CL intensity was linearly related to the concentration of naproxen from 4.0×10⁻⁹ to 1.0×10⁻⁶gmL⁻¹ ( r=0.9993). The detection limit was 2×10⁻⁹gmL⁻¹ naproxen, the relative standard deviation for 1.0×10⁻⁷gmL⁻¹ naproxen solution was 1.5% ( n=11) and the sampling frequency was 120h⁻¹. The method was applied to the determination of naproxen in pharmaceutical preparation with satisfactory results. The mechanism of CL reaction was discussed briefly.

Keywords: Chemiluminescence; Flow injection; Naproxen; KMnO; ₄

Flow injection chemiluminescence determination of naproxen based on KMnO₄–Na₂SO₃ reaction in neutral aqueous medium by Yinhuan Li; Jiuru Lu (pp. 107-110).

Keywords: Chemiluminescence; Flow injection; Naproxen; KMnO; ₄

A novel approach for the rapid decomposition of Actinide™ resin and its application to measurement of uranium and plutonium in natural waters by I.W. Croudace; P.E. Warwick; R.C. Greenwood (pp. 111-118).

A rapid and robust procedure is described for the decomposition of Actinide™ resin permitting the routine application of this resin as a preconcentrator. Although the classical Fe(OH)₃ precipitation is effective in scavenging actinides, the need for careful handling to recover the sticky precipitate makes the new method much more attractive. The known difficulty of decomposing Actinide™ resin, which is required prior to the subsequent separation of adsorbed actinides, is innovatively overcome by using a borate fusion attack. This procedure effectively solves the normally encountered problem by safely and speedily decomposing the resin in minutes rather than hours. The alternative and apparently simpler technique of direct ashing of the Actinide™ resin is not used since it leads to a residue that is not readily leachable. The new technique has been incorporated into a procedure for the isolation of Pu and U from natural water samples and their subsequent quantification by alpha spectrometry. The efficiency of loading of the elements onto Actinide™ resin has been tested using both batch and column-based approaches. The integrated method involving Actinide™ resin preconcentration, borate fusion, anion and UTEVA chromatography and electrodeposition provides limits of detection of 0.001BqL⁻¹ and chemical recoveries in excess of 80% from groundwater and seawater samples as large as 5L. Comparative data, presented for the analysis of independently analysed river, borehole and surface run-off waters using both the described procedure and other competing techniques, show very good agreement.

Keywords: Actinides; Actinide™ resin; Borate fusion; Alpha spectrometry; Natural waters; Plutonium; Uranium

Development of an ultrasound-assisted extraction method for biomonitoring of vanadium and nickel in the coastal environment under the influence of the Prestige fuel spill (North east Atlantic Ocean) by I. Lavilla; P. Vilas; J. Millos; C. Bendicho (pp. 119-125).

As a consequence of the Prestige shipwreck occurred in the Northeast Atlantic Ocean in November 2002, the need for establishing the environmental impact caused by metals has been of primary concern. Among the different metals contained in the fuel spill, V and Ni are particularly of interest since they appear at relatively high concentration in the original fuel. Biomonitoring of V and Ni using wild mussels ( Mytilus edulis) collected along the Galician Coast (NW Iberian Peninsula) has been performed. Ultrasound-assisted extraction of V and Ni from dried mussel tissues using probe sonication allowed a fast solid–liquid extraction thus facilitating sample preparation from large sample batches used for biomonitoring. V and Ni were determined in shellfish caught in the Galician littoral and tar balls from the Prestige spill by electrothermal-atomic absorption spectrometry and inductively coupled plasma-optical emission spectrometry, respectively. A Plackett–Burman saturated design was applied for screening optimization of variables influencing the ultrasound-assisted extraction of V and Ni from shellfish. Efficient extraction of both metals was obtained from slurries prepared in 2mL capacity sample vials (10mg sample with a particle size less than 100μm) using a 3% (v/v) HNO₃ diluent and subjected to probe sonication (3min; 30% vibrational amplitude of the probe). The method was successfully validated by means of three certified reference materials: NRCC-TORT-2 Lobster hepatopancreas, NIST-SRM 1566b Oyster tissue and NIST-SRM 2977 Mussel tissue. The detection limit (LOD) of V and Ni in the marine biological tissues, calculated according to the 3 σ criterion, were 0.24μgg⁻¹ and 0.15μgg⁻¹ for V and Ni, respectively. V and Ni concentrations in M. edulis were in the range 1.7–4.8 and 0.8–2.8μgg⁻¹, respectively. Whilst no significant variations in Ni contents were observed in regard to reference values, an important increase in V concentration is observed at some sampling points, thereby indicating bioaccumulation.

Keywords: Vanadium; Nickel; Ultrasound-assisted extraction; Fuel spill; Biomonitoring; Shellfish

Extraction and determination of elemental selenium in sediments—A comparative study by Yu-Wei Chen; Lu Li; Alessandro D’Ulivo; Nelson Belzile (pp. 126-133).

This paper proposes a new technique to extract elemental Se from soil and sediment samples. In this study, we have identified that the purchased red elemental selenium standard (PF-Se) was impure and rather consisted of a mixture of CS₂ soluble amorphous elemental Se ( ca. 10%, w/w), water soluble oxidized Se ( ca. 15–17%, w/w) and, CS₂ insoluble red monoclinic elemental Se. In more recent studies, a slow oxidation and a mineral phase transition of this sample was also observed. The solubility of the amorphous elemental Se in CS₂ was at least 0.64mgL⁻¹. The black elemental Se purchased from Sigma–Aldrich had a much lower solubility in CS₂ (7.2μgmL⁻¹) compared to that given in the literature. Any selenium compounds with electrical charge and polar nature is insoluble in CS₂. In a sodium sulphite solution, PF-Se was completely dissolved thus giving a clear indication of the lack of selectivity in that extraction system. Other comparative studies also demonstrated that over extraction did occur with the Na₂SO₃ method. Compared to Na₂SO₃, CS₂ extraction of elemental Se is not only much simpler, straightforward and with higher analytical precision, but also much more selective and accurate. With HG-AFS, the detection limit can reach as low as 1.0ngg⁻¹ in sediment sample owing to a low reagent blank of CS₂ solvent.

Keywords: Elemental selenium; Extraction; Speciation; Carbon disulphide; Solubility; Sediment; Hydride generation-atomic fluorescence spectrometry

Extraction and determination of elemental selenium in sediments—A comparative study by Yu-Wei Chen; Lu Li; Alessandro D’Ulivo; Nelson Belzile (pp. 126-133).

Keywords: Elemental selenium; Extraction; Speciation; Carbon disulphide; Solubility; Sediment; Hydride generation-atomic fluorescence spectrometry

Flow injection system for potentiometric determination of alkaline phosphatase inhibitors by Robert Koncki; Katarzyna Rudnicka; �?ukasz Tymecki (pp. 134-139).

A simple flow injection system for potentiometric detection of alkaline phosphatase (ALP) activity has been developed and adapted for determination of selected inhibitors of this enzyme. In this system monofluorophosphate (MFP) has been applied as a specific ALP substrate. The use of this substrate enables application of fluoride ion selective electrode (FISE) as a detector of the product of the enzyme catalyzed reaction. Moreover, chemical stability and low cost of MFP enables the use of the substrate as a component of the carrier. This way, fluoride ions contained in this substrate define and stabilize baseline signal generated by the detector. Effects from several potential ALP inhibitors and interfering species were studied and discussed. The system allows inhibitive detection of beryllium and vanadate ions at ppb levels with relatively high selectivity, short time of analysis and high throughput of the system (near 8samplesh⁻¹).

Keywords: Flow injection analysis; Fluoride ion selective electrode; Alkaline phosphatase; Inhibitors; Beryllium; Vanadate

Flow injection system for potentiometric determination of alkaline phosphatase inhibitors by Robert Koncki; Katarzyna Rudnicka; Łukasz Tymecki (pp. 134-139).

Keywords: Flow injection analysis; Fluoride ion selective electrode; Alkaline phosphatase; Inhibitors; Beryllium; Vanadate

Elucidation of molecular and elementary composition of organic and inorganic substances involved in 19th century wax sculptures using an integrated analytical approach by M. Regert; J. Langlois; E. Laval; A.-S. Le Hô; S. Pagès-Camagna (pp. 140-152).

Wax sculptures contain several materials from both organic and inorganic nature. These works of art are particularly fragile. Determining their chemical composition is thus of prime importance for their preservation. The identification of the recipes of waxy pastes used through time also provides valuable information in the field of art history.The aim of the present research was to develop a convenient analytical strategy, as non-invasive as possible, that allows to identify the wide range of materials involved in wax sculptures.A multi-step analytical methodology, based on the use of complementary techniques, either non- or micro-destructive, was elaborated. X-ray fluorescence and micro-Raman spectroscopy were used in a non-invasive way to identify inorganic pigments, opacifiers and extenders. The combination of structural and separative techniques, namely infrared spectroscopy, direct inlet electron ionisation mass spectrometry and high temperature gas chromatography, was shown to be appropriate for unravelling the precise composition of the organic substances. A micro-chemical test was also performed for the detection of starch.From this study it has been possible to elucidate the composition of the waxy pastes used by three different sculptors at the end of the 19th century. Complex and elaborated recipes, in which a large range of natural substances were combined, were highlighted.

Keywords: Infrared spectroscopy; Raman spectroscopy; Mass spectrometry; High temperature gas chromatography–mass spectrometry; Wax sculptures; Cultural heritage; Beeswax; Japan wax; Pine resin; Paraffin; Pigments

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Analytica Chimica Acta (v.577, #1)