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Analytica Chimica Acta (v.549, #1-2)

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

Contents (pp. v-vi).

Calendar of forthcoming meetings (pp. n1-n2).

Amperometric sensing in the gas-phase by Ren� Knake; Patrick Jacquinot; Alexia W.E. Hodgson; Peter C. Hauser (pp. 1-9).

The design of amperometric sensors for gaseous species presents a challenge as the gas phase has to be brought into contact with a solid electrode as well as an electrolyte phase which usually is liquid. However, many species of analytical interest are electroactive, such as SO₂, NO_x, O₃, CO, formaldehyde or ethanol, and electrochemical means are always attractive in designing sensors because the electronic signal is obtained directly. Therefore, different approaches have been implemented and some types of such sensors have been available commercially for quite some time. Nevertheless, many new developments with regard to an improvement of sensitivity, selectivity and in the construction of these devices have been reported over the last few years, as well as approaches to miniaturization. In this review it is attempted to give an overview of the state of the art of this field, highlighting recent developments.

Keywords: Sensor; Amperometric; Gas; Gas-diffusion electrode; Solid polymer electrolyte

A sensitive and selective “turn on�? fluorescent chemosensor for Hg(II) ion based on a new pyrene–thymine dyad by Zhuo Wang; Deqing Zhang; Daoben Zhu (pp. 10-13).

Strong pyrene excimer emission was observed for a new pyrene–thymine dyad that can be easily synthesized in the presence of Hg²⁺ ion. But, the enhancement of pyrene excimer emission was not detected in the presence of other metal ions. As a result, this new pyrene–thymine dyad is suited for use as a sensitive and selective “turn on�? fluorescent chemosensor for Hg(II) ion.

Keywords: Hg(II) ion; Chemosensor; Pyrene; Thymine; Excimer emission; Fluorescence

Real-time monitoring of reactive oxygen species production during differentiation of human monocytic cell lines (THP-1) by Shigenobu Kasai; Hitoshi Shiku; Yu-suke Torisawa; Hiroyuki Noda; Jun Yoshitake; Takuo Shiraishi; Tomoyuki Yasukawa; Toshiaki Watanabe; Tomokazu Matsue; Tetsuhiko Yoshimura (pp. 14-19).

Human monocytic leukemia cell line THP-1 differentiates into macrophages by phorbol myristate acetate (PMA) treatment. We report real-time monitoring of reactive oxygen species (ROS) production during the differentiation process. The production of ROS by THP-1 with several hours time scale has been detected using electrochemical and chemiluminescence methods. The increase in oxidation current derived from ROS arising from THP-1 was observed between 1 and 10h after the commencement of treatment with 20nM PMA. The response was unusually slow compared to the quick oxidative response observed in the macrophages. Chemiluminescence methods were used to further investigate the ROS production rate by carrying out treatment with 20nM to 100μM PMA. The chemiluminescence responses were found to be faster for the cells treated with higher concentrations of PMA. The time scale of the oxidative response monitored using the chemiluminescence method correlated with that recorded using a microelectrode. The slow time scale of ROS production reflects the differentiation rate of THP-1 into macrophages. The effect of inhibitors on NADPH oxidase and NO synthase were also examined to find that the superoxide anion is the main radical produced from NADPH oxidase.

Keywords: THP-1; Differentiation; Reactive oxygen species; Chemiluminescence; Electrochemical method

Surface-modified CdSe quantum dots for the sensitive and selective determination of Cu(II) in aqueous solutions by luminescent measurements by Maria Teresa Fern�ndez-Arg�elles; Wei Jun Jin; Jos� M. Costa-Fern�ndez; Rosario Pereiro; Alfredo Sanz-Medel (pp. 20-25).

The use of water-soluble luminescent CdSe quantum dots (QDs), whose surface was modified either with 2-mercaptoethane sulphonic acid or with 2-mercaptoacetic acid, was investigated for the sensitive and selective determination of copper(II) ions in aqueous solutions. A pH 5.5 was selected for measurement. Also, the effect of the presence of different surfactant agents in the sample solution, in order to stabilize the fluorescent signals of the QDs in water, has been investigated. A 10⁻³M of dodecyltrimethylammonium chloride final concentration was selected. Fluorescence signals were found to be stable for at least several days in such conditions.Higher sensitivity was obtained for the sulphonic-modified CdSe QDs. Detection limits for Cu(II) of 0.2μgl⁻¹, a dynamic range up to 30μgl⁻¹, and a R.S.D. of ±2.8% for 10 replicates of a 2.5μgl⁻¹ Cu(II) solution were obtained as analytical performance characteristics. Besides, the influence on the fluorescence signal of foreign cations, including Na⁺, K⁺, Ca²⁺, Mg²⁺, Zn²⁺, Mn²⁺, Co³⁺, Ag⁺, Hg²⁺ and Fe³⁺ was studied (to avoid inner filter effect, the colourless complex FeF₆³⁻ was investigated instead of Fe³⁺). Results showed a high selectivity of the sulphonic-modified QDs towards Cu(II) ions. The proposed method demonstrated improved sensitivity and selectivity characteristics for Cu(II) determinations as compared to other already described luminescence QDs-based analytical methods for metal ions determinations.Analytical applicability of the QDs has been demonstrated by tap and fountain water analysis. Results of Cu(II) determinations were in good agreement to those obtained by using an alternative analytical method.

Keywords: Quantum dots; Surface modifications; Luminescence; Copper ions determination

Fluorimetric study of the interaction between nicotinamide adenine dinucleotide phosphate and tetracycline–europium complex and its application by Qian Peng; Faju Hou; Xiaoxia Ge; Chongqiu Jiang; Shubo Gong (pp. 26-31).

A new spectrofluorimetric method was developed for the determination of trace amount of nicotinamide adenine dinucleotide phosphate (NADP). Using europium (Eu³⁺)–tetracycline (TC) complex as a fluorescent probe, in the buffer solution of pH 7.60. NADP can remarkably enhance the fluorescence intensity of the Eu³⁺–TC complex at λ=612nm and the enhanced fluorescence intensity of Eu³⁺ ion is in proportion to the concentration of NADP. Optimum conditions for the determination of NADP were also investigated. The dynamic range for the determination of NADP is 4.4×10⁻⁷ to 2.2×10⁻⁶moll⁻¹ with detection limit of 6.9×10⁻⁸moll⁻¹. This method is simple, practical and relatively free interference from coexisting substances and can be successfully applied to determination of NADP in synthetic water samples and in serum samples. Moreover, the enhancement mechanisms of the fluorescence intensity in the Eu³⁺–TC system and the Eu³⁺–TC–NADP system have been also discussed.

Keywords: Nicotinamide adenine dinucleotide phosphate (CoII or NADP); Tetracycline (TC); Europium (Eu; ³⁺; ); Spectrofluorimetric method

Determination of protein with methylene blue-sodium tetraphenylborate phosphorescence probe solid substrate-room temperature phosphorimetry by Jia-Ming Liu; Shi-rong Hu; Zhi-yong Yang; Xue-Lin Li; Ping-ping Li; Huan-huan Xu; Guo-hui Zhu; Long-Di Li (pp. 32-38).

A new sensitive method for the determination of protein has been established based on methylene blue-sodium tetraphenylborate phosphorescence probe solid substrate-room temperature phosphorescence (SS-RTP) sensitization. Methylene blue (MB) can not only exist as nitrogen quinine cation structure in the acidity agent but also associate with anion of [B(C₆H₅)₄]⁻. According to the facts above, ionic association of [MB]⁺[B(C₆H₅)₄]⁻ can emit strong and stable SS-RTP on acetyl cellulose membrane. It is found that the SS-RTP intensity of luminescence system is increased sharply in the presence of bovine serum albumin (BSA). Under the optimum condition, the linear dynamic range of this method is 0.044–17.6agspot⁻¹ (corresponding concentration: 0.11–44.0fgml⁻¹, the sample volume: 0.4μlspot⁻¹), and the regression equation can be expressed as Δ I_p=20.80+9.702m_BSA (agspot⁻¹) with the correlation coefficient r=0.9995 ( n=6). The detection limit of this method is 13.3zgspot⁻¹ (corresponding concentration: 33agml⁻¹). This sensitive, accurate, selective and repeatable method has been applied to determine the content of protein in real samples with satisfactory results. The reaction mechanism for determination of protein by methylene blue-sodium tetraphenylborate phosphorescence probe SS-RTP sensitization has also been discussed.

Keywords: Protein; Methylene blue-sodium tetrophenylborate phosphorescence probe; Solid substrate-room temperature phosphorimetry (SS-RTP); Sensitization

Theoretical and experimental study of nicotinamide molecularly imprinted polymers with different porogens by Liqing Wu; Kuaichang Zhu; Meiping Zhao; Yuanzong Li (pp. 39-44).

Based on the computational model proposed in our previous work, a comparative study of the influence of porogens on the affinity and selectivity of MIP was carried out in this paper. Nicotinamide (NAM) was chosen as the template and methacrylic acid (MAA) was chosen as the functional monomer. The interaction energy values between NAM and MAA were calculated with methanol, acetonitrile, chloroform and toluene as the porogens, respectively. The subsequent chromatographic evaluation was carried out to give the retention factors and selectivity factors of NAM and its analogues. Good correlations were found to exist between the interaction energies and the retention factors or selectivity factors. When the porogens had poor hydrogen bonding capacity, the interaction energy was mainly influenced by dielectric constant of solvent. And when the porogen had strong capacity in forming hydrogen bond, both the dielectric constant of the solvent and the hydrogen bonding interference affected the forming of the template–monomer complex and the corresponding interaction energy. Aprotic porogen with low dielectric constant was likely to lead to large interaction energy between the template and the functional monomer, resulting in a MIP with better affinity and selectivity. The success of the predicting model provides a experiment-free way for the selection of porogen for given template and functional monomer.

Keywords: Molecular recognition; Molecularly imprinted polymer (MIP); Theoretical; Porogen; Solvent effect

Selective separation of brominated bisphenol A homologues using a polymer-based medium prepared by the fragment imprinting technique by Takuya Kubo; Ken Hosoya; Tomoharu Sano; Makoto Nomachi; Nobuo Tanaka; Kunimitsu Kaya (pp. 45-50).

To achieve the selective separation of brominated aromatic compounds, the polymer-based separation media were prepared by the fragment imprinting technique and were evaluated with high-performance liquid chromatography. In the results, the separation medium prepared with 2,6-bis-(trifluoromethyl)-benzoic acid as the template showed the selective retention abilities for 3,5- and/or 3′,5′-brominated or chlorinated bisphenol A homologues. The selective retention seems due to the shape recognition according to the alternative template molecule. Especially, the tetrabromo- or tetrachloro-bisphenol A homologues were selectively recognized by the imprinting effect.

Keywords: Fragment imprinting; Selective retention; Brominated or chlorinated bisphenol A; Alternative template molecules

Synthesis, characterization, and analytical applications of erbium(III) ion imprinted polymer particles prepared via γ-irradiation with different functional and crosslinking monomers by R. Kala; V.M. Biju; T. Prasada Rao (pp. 51-58).

Erbium(III) ion imprinted polymer (IIP) particles were synthesized by preparing erbium(III)–5,7-dichloroquinoline-8-ol–4-vinylpyridine prepolymer complex and then copolymerizing via γ-irradiation with different functional and crosslinking monomer combinations, viz. styrene–divinyl benzene, 2-hydroxyethyl methacrylate (HEMA)–ethylene glycoldimethacrylate (EGDMA), methyl methacrylate (MMA)–EGDMA. The erbium(III) imprint ion was removed by stirring the above particles with 6.0moll⁻¹ HCl to obtain leached IIP particles. Control polymer (CP) particles were prepared without imprint ion. Again, CP, unleached and leached IIP particles were characterized by XRD, UV–vis spectrophotometric, pore size, SEM, and swelling ratio studies. The preconcentration of traces of erbium(III) during rebinding with leached IIP particles was studied as a function of pH, weight of polymer material, preconcentration and elution times, eluent concentration and volume, and aqueous phase volume. These studies indicate that as low as 2μg of erbium(III) present in 500ml can be preconcentrated into 20ml of 1.0moll⁻¹ HCl, and thus providing an enrichment factor of ∼25. Furthermore, the present study indicates that styrene–divinyl benzene-based IIP could be a better choice for the separation of erbium(III) from yttrium(III), dysprosium(III), holmium(III), and thulium(III) compared to HEMA–EGDMA and MMA–EGDMA-based IIPs.

Keywords: γ-Radiation; Ion imprinted polymers; Functional and crosslinking monomers; Lanthanides

A polymeric junction membrane for solid-state reference electrodes by Jeonghan Ha; Steven M. Martin; Youngho Jeon; In Jun Yoon; Richard B. Brown; Hakhyun Nam; Geun Sig Cha (pp. 59-66).

A polymer membrane system composed of 30wt.% cellulose acetate (CA) and polyurethane (PU) has been developed for the fabrication of mass producible solid-state reference electrodes. The CA/PU membrane exhibits appropriate adhesion to common substrates (e.g., ceramic and silicon chips) of miniaturized electrochemical sensors, allows quick hydration of internal hydrogel layer (3M KCl with a 6wt.% water soluble polymer) deposited on micro-patterned electrodes resulting in fast preconditioning time (∼100s), and provides a stable reference potential for an extended period (use-lifetime: 25–90min) by limiting the diffusion of internal electrolytes. The potentiometric responses of the CA/PU membrane-based solid-state reference electrodes drifted rapidly (40–90mV/h) after their use-lifetime; the results suggest that the internal electrolyte slowly fills the micro-channels of the outer membrane while maintaining stable potential, and begins to diffuse away at an increased rate from the membrane/aqueous solution interface. The potentiometric responses of the polymer membrane-based ion-selective electrodes (for Na⁺, K⁺, Ca²⁺, Cl⁻ and H⁺) formed on the same chip with the CA/PU membrane-coated Ag/AgCl reference electrode were examined both in aqueous and physiological samples; their analytical performance closely matched that of sensors measured against a conventional reference electrode.

Keywords: Ion-selective electrode; Reference electrode; Liquid junction; Cellulose acetate; Polyurethane

Square-wave adsorptive stripping voltammetry for the determination of cyclofenil after photochemical derivatization by Wagner F. Pacheco; P�rcio A.M. Farias; Ricardo Q. Aucelio (pp. 67-73).

Square-wave adsorptive voltammetry was applied for the determination of cyclofenil at ultra-trace levels. Due to the unstable behavior of cyclofenil, the analyte photochemical derivative was used for quantification. This stable analyte photoderivative was pre-concentrated (30s accumulation time) on the hanging mercury drop electrode (HMDE), using Britton–Robinson buffer (pH 9) as the supporting electrolyte. Under these conditions, the cyclofenil photoderivative presented one reduction peak maximum at −1280mV. Instrumental and experimental parameters were carefully optimised. Limit of detection of 1.5×10⁻⁸moll⁻¹, was achieved with a linear dynamic range from 5×10⁻⁸ to 6×10⁻⁶moll⁻¹. This analytical approach was tested through the analysis of one commercial pharmaceutical formulation and analyte spiked urine samples. While no interferences were observed for the analysis of the pharmaceutical tablet, urine samples imposed interferences that were corrected by using the analyte addition technique. Recovery tests enabled results from 93.6 to 106.5%. Repeatability of the measurements was below 7% at 1×10⁻⁶moll⁻¹ concentration level.

Keywords: Cyclofenil; Stripping voltammetry; Photochemical derivatization; Square-wave technique

Optimization of the experimental parameters in the determination of lamotrigine by adsorptive stripping voltammetry by M. Encarnaci�n Burgoa Calvo; Olga Dom�nguez Renedo; M. Julia Arcos Mart�nez (pp. 74-80).

This paper describes a procedure that has been optimized for the determination of lamotrigine (LTG) by adsorptive stripping voltammetry (AdSV). Two different voltammetric techniques, namely differential pulse adsorptive stripping voltammetry (DPAdSV) and square wave adsorptive stripping voltammetry (SWAdSV) were used. In order to determine the most sensitive technique, optimization of the experimental parameters using experimental design methodology was carried out for each technique. The detection limits obtained, 4.68×10⁻⁹moldm⁻³ for DPAdSV and 5.02×10⁻⁹moldm⁻³ for SWAdSV, show that both techniques are almost the same sensitive for the analysis of lamotrigine. Finally, this method was used to determine lamotrigine in pharmaceutical preparations and in spiked human plasma samples.

Keywords: Lamotrigine; Differential pulse adsorptive stripping voltammetry; Square wave adsorptive stripping voltammetry; Experimental design

Capillary zone electrophoresis separation of low concentration stimulants in human urine with laser-induced fluorescence detection by Xiuhan Yang; Xiaochuan Wang; Xiangmin Zhang (pp. 81-87).

Capillary zone electrophoresis separation with laser-induced fluorescence (LIF) detection for the determination of fluorescein isothiocyanate (FITC) derivatized stimulants (ephedrine, phenylpropanolamine and heptaminol) was demonstrated. A simple electrophoretic buffer system composed of 30mM triethylamine was selected and high voltage of 16kV was applied for the capillary electrophoresis separations. Stimulants in human urine were extracted by organic solvents and then derivatized with FITC. By employing a semiconductor laser-induced fluorescence detector, low concentration stimulants of 22ng/mL can be detected within 10min. Operation conditions for derivatization and separation were discussed. This simple CZE–LIF method with sensitive detection provided the possibility to develop the on-chip stimulants screening methods for doping control.

Keywords: Semiconductor laser-induced fluorescence detection; Capillary zone electrophoresis; Ephedrine; Phenylpropanolamine; Heptaminol

Method development and validation for the simultaneous determination of rosiglitazone and metformin in pharmaceutical preparations by capillary zone electrophoresis by Ceren Yardımcı; Nuran Özaltın (pp. 88-95).

A novel and simple capillary zone electrophoresis method was developed and validated for the simultaneous determination of rosiglitazone and metformin in pharmaceutical preparations. The optimum separation for these analytes was achieved in <9min at 25°C with a fused-silica capillary column (80.5cm×75μm i.d., effective length 72.0cm) and a running buffer containing 25mM acetate buffer at pH 4.0. The samples were injected hydrodynamically for 3s at 50mbar and the applied voltage was +25.0kV. Detection wavelength was set at 203nm. Verapamil was used as internal standard. The method was suitably validated with respect to specificity, linearity, limit of detection and quantitation, accuracy, precision, and robustness. The limits of detection and quantitation were 0.5 and 1.0μgmL⁻¹ for rosiglitazone and metformin, respectively. The method developed was successfully applied to the simultaneous determination of rosiglitazone and metformin in pharmaceutical preparations. The results were compared to a liquid chromatographic method reported in the literature and no significant difference was found statistically.

Keywords: Rosiglitazone; Metformin; Simultaneous determination; Capillary zone electrophoresis; Validation; Drug analysis

Chiral liquid chromatographic determination of mirtazapine in human plasma using two-phase liquid-phase microextraction for sample preparation by Fernando Jos� Malague�o de Santana; Anderson Rodrigo Moraes de Oliveira; Pierina Sueli Bonato (pp. 96-103).

A simple, inexpensive and efficient preconcentration and clean-up liquid-phase microextraction method (LPME) using porous polypropylene hollow fibre membrane was developed for the extraction of the antidepressant mirtazapine from human plasma. The effects of different parameters influencing the efficiency of extraction were described and optimized. Under optimized conditions, mirtazapine was extracted with 22μl toluene from 0.7ml of plasma previously diluted with 3.1ml deionized water and alkalinized with 0.15ml 10M NaOH. Mefloquine was used as internal standard. The chromatographic analysis was carried out through chiral liquid chromatography (LC) using a Chiralpak AD column and hexane–ethanol (98:2, v/v) plus 0.1% diethylamine as mobile phase, at a flow rate of 1.5mlmin⁻¹. Detection was carried out at 292nm. The mean recoveries of (+)-( S)- and (−)-( R)- mirtazapine were 29.1 and 28.8%, respectively. The quantification limit (LOQ) was 6.25ngml⁻¹ with linear response over the 6.25–625ngml⁻¹ concentration range for both enantiomers. Within-day and between-day assay precision and accuracy were studied at three concentration levels (15, 100 and 500ngml⁻¹). For both mirtazapine enantiomers, the coefficients of variation (CV) and deviation from the theoretical values were lower than 15% at all concentration levels. The developed and validated method showed that LPME is a promising technique for sample preparation for the analyses of chiral drugs in biological samples.

Keywords: Liquid-phase microextraction; Porous polypropylene hollow fiber; Liquid chromatography; Enantiomeric separation; Mirtazapine; Plasma

Pressurized liquid extraction using water/isopropanol coupled with solid-phase extraction cleanup for semivolatile organic compounds, polycyclic aromatic hydrocarbons (PAH), and alkylated PAH homolog groups in sediment by Mark R. Burkhardt; Steven D. Zaugg; Teresa L. Burbank; Mary C. Olson; Jana L. Iverson (pp. 104-116).

Polycyclic aromatic hydrocarbons (PAH) are recognized as environmentally relevant for their potential adverse effects on human and ecosystem health. This paper describes a method to determine the distribution of PAH and alkylated homolog groups in sediment samples. Pressurized liquid extraction (PLE), coupled with solid-phase extraction (SPE) cleanup, was developed to decrease sample preparation time, to reduce solvent consumption, and to minimize background interferences for full-scan GC–MS analysis. Recoveries from spiked Ottawa sand, environmental stream sediment, and commercially available topsoil, fortified at 1.5–15μg per compound, averaged 94.6±7.8%, 90.7±5.8% and 92.8±12.8%, respectively. Initial method detection limits for single-component compounds ranged from 20 to 302μg/kg, based on 25g samples. Results from 28 environmental sediment samples, excluding homologs, show 35 of 41 compounds (85.4%) were detected in at least one sample with concentrations ranging from 20 to 100,000μg/kg. The most frequently detected compound, 2,6-dimethylnaphthalene, was detected in 23 of the 28 (82%) environmental samples with a concentration ranging from 15 to 907μg/kg. The results from the 28 environmental sediment samples for the homolog series showed that 27 of 28 (96%) samples had at least one homolog series present at concentrations ranging from 20 to 89,000μg/kg. The most frequently detected homolog series, C₂-alkylated naphthalene, was detected in 26 of the 28 (93%) environmental samples with a concentration ranging from 25 to 3900μg/kg. Results for a standard reference material using dichloromethane Soxhlet-based extraction also are compared.

Keywords: Polycyclic aromatic hydrocarbon; Pressurized liquid extraction; Solid-phase extraction; Sediment

Development of a solid-phase extraction method for the simultaneous determination of chloroanisoles and chlorophenols in red wine using gas chromatography–tandem mass spectrometry by Almudena Mart�nez-Uru�uela; Isaac Rodr�guez; Rafael Cela; Jos� Mar�a Gonz�lez-S�iz; Consuelo Pizarro (pp. 117-123).

A procedure for the determination of three chloroanisoles (2,4,6-trichloro, 2,3,4,6-tetrachloro and pentachloroanisol), as well as their precursor chlorophenols (2,4,6-trichloro, 2,3,4,6-tetrachloro and pentachlorophenol), involved in the presence of cork taint in red wine has been developed. Samples, up to 1l, were concentrated using a 200mg Oasis HLB solid-phase extraction (SPE) cartridge. Chlorophenols were quantitatively eluted from this sorbent with 3ml of methanol. Chloroanisoles were mainly recovered in a second fraction of n-hexane (2ml). Both fractions were combined and mixed with an aqueous solution of sodium bicarbonate and 50μl of acetic anhydride. Chlorophenols were acetylated in the aqueous-methanolic phase and extracted to n-hexane. Chloroanisoles remained unaffected in the n-hexane layer. Both groups of compounds were determined by gas chromatography–tandem mass spectrometry in the same chromatographic analysis. Using a temperature programmable vaporization injector detection limits from 0.2 to 2.4ngl⁻¹, below their sensorial threshold level in red wine, were obtained for all compounds. Average recoveries higher than 80% and acceptable precision were achieved using red wine samples spiked with the analytes at different concentration levels.

Keywords: Wine; Cork taint; Chloroanisoles; Chlorophenols; Solid-phase extraction; Gas chromatography–electron-capture detection; Gas chromatography–tandem mass spectrometry; CarboFrit™

Simultaneous preconcentration of Cu, Fe and Pb as methylthymol blue complexes on naphthalene adsorbent and flame atomic absorption determination by Nahid Pourreza; Reza Hoveizavi (pp. 124-128).

A simultaneous preconcentration method was developed for determination of trace amounts of Cu, Fe and Pb by atomic absorption spectrometry. The method is based on the retention of their methylthymol blue complexes by naphthalene methyltrioctyl ammonium chloride adsorbent in a column. The adsorbed metal complexes were eluted from the column with nitric acid and Cu, Fe and Pb were determined by flame atomic absorption spectrometry. Several parameters such as pH of the sample solution, ligand concentration, volume of the sample and the amount of methyltrioctyl ammonium chloride loaded on naphthalene were evaluated. The effect of diverse ions on the preconcentration was also investigated. A preconcentration factor of up to 100 or more can easily be achieved depending on the volume of the sample taken. The calibration graphs were obtained in the range of 5–40, 10–100 and 10–200ngml⁻¹ for Cu, Fe and Pb in the initial solution, respectively, when using 500ml of the solution. The detection limit based on three standard deviations of the blank was 0.54, 3.1, and 4.5ngml⁻¹ for Cu, Fe and Pb, respectively. The relative standard deviations (R.S.D.) of 0.62–1.4% for Cu, 1.9–3.4% for Fe and 1.0–2.2% for Pb were obtained. The method was applied to the determination of Cu, Fe and Pb in river and wastewater samples.

Keywords: Solid-phase; Preconcentration; Lead; Iron; Copper; Methylthymol blue and naphthalene–methyltrioctyl ammonium chloride

Estimation ofl-5-hydroxytryptophan in rat serum and Griffonia seed extracts by liquid chromatography–mass spectrometry by Gopalarao Koppisetti; Anilkumar Siriki; Kannababu Sukala; Gottumukkala V. Subbaraju (pp. 129-133).

The application of liquid chromatography–mass spectrometry (LC–MS) was investigated for the analysis ofl-5-hydroxytryptophan (5-HTP) in rat serum. The chromatographic elution was carried out using C₁₈ column (YMC, 250mm×2mm, 5μm) with a mobile phase water: acetonitrile (93:7, v/v). Quantitative analysis was performed by negative ion mode using selective ion monitoring (SIM) method with electrospray ionization interface. The serum samples were de-proteinized with acetonitrile. The limit of detection (LOD) and limit of quantification (LOQ) in the serum was found to be 2 and 6ng and calibration curve ranging from 5 to 17ngμl⁻¹ showed to be linear with correlation coefficient 0.994±0.0006. Within-day and day-to-day reproducibility were 0.39–0.44% and 0.66–1.67%, respectively and the recoveries of 5-HTP in the serum were 94.65–95.46%. The method developed was also found to be applicable for the analysis of Griffonia simplicifolia seed extracts and dosage forms with LOD and LOQ, 0.02 and 0.05ng, respectively and linearity range 3–20ngμl⁻¹ with a correlation coefficient of 0.9992±0.0004. The recoveries in the extracts were 97.00–100.20% and %R.S.D. of the intra- and inter-day precision was found to be 0.27–1.29% and 0.35–1.12%.

Keywords: Liquid chromatography–mass spectrometry; l; -5-Hydroxytryptophan; Serum; Dosage forms

Temperature dependence of solvation heat capacities by gas chromatography by Zoltan A. Fekete; K�roly H�berger; Zolt�n Kir�ly; Mikl�s G�rg�nyi (pp. 134-139).

The temperature dependence of molar solvation heat capacity has been determined in the temperature range of 30–160°C for C₆–C₁₀ n-alkanes and McReynolds test compounds on 100% poly(dimethylsiloxane) (PDMS) FSOT columns using the equations involving the temperature dependence of solvation enthalpy and entropy. The evaluation method is based on a rigorous statistical evaluation of the parameter estimations. On PDMS, column solvation heat capacity versus temperature curves are S-shaped for n-alkanes and for 1-butanol, while the temperature dependence of the other test compounds is more complicated. The results show near monotonous decrease of solvation heat capacity in the whole temperature range. Harmonic oscillator—rigid rotor assumption rationalizes the curves in a simplified way.

Keywords: Gas chromatography; Solvation molar heat capacity; Temperature dependence; Statistical mechanics

Properties and analytical application of PQQ-dependent glycerol dehydrogenase from Gluconobacter sp. 33 by I. Lapenaite; B. Kurtinaitiene; J. Razumiene; V. Laurinavicius; L. Marcinkeviciene; I. Bachmatova; R. Meskys; A. Ramanavicius (pp. 140-150).

PQQ-dependent glycerol dehydrogenase (GlyDH) was purified from Gluconobacter sp. 33. Activation of this enzyme by Ca⁺⁺ and Mg⁺⁺ ions and PQQ was analysed. The purified GlyDH displayed an optimum activity at pH 7.0–7.5 and was the most stable at pH 8.5–9.5. It was determined that the rate of glycerol oxidation had a maximum at 33–37°C. However, a rapid enzyme inactivation began at the temperatures higher than 35°C. The calculated K_M values for glycerol,d-sorbitol, andd-mannitol were 0.83, 1.0, and 2.4mM, respectively. Several different designs of enzymatic electrodes were constructed and involved into glycerol biosensor design. Investigation of substrate selectivity of immobilised (cross-linked by glutaraldehyde) GlyDH shows, that immobilisation procedure decreases the activity of the membranes of Gluconobacter sp. 33 cells (mGlyDH) for glucose, sorbitol, mannitol, and ethanol, but increases the activity of mGlyDH for methanol and dulcitol. Soluble phenazine methosulphate (PMS) and insoluble 4-ferrocenylphenol (FP), N-(4-hydroxybenzylidene)-4-ferrocenylaniline (HBFA) were applied for construction of GlyDH-based biosensors. Inactivation of GlyDH by heavy metal ions was investigated and it was observed that biosensors based on membranes of Gluconobacter sp. 33 cells (mGlyDH) and purified PQQ-dependent glycerol dehydrogenase (pGlyDH) were sensitive to Pb⁺⁺, Cd⁺⁺, Co⁺⁺, Cu⁺⁺, Ni⁺⁺, and Hg⁺⁺. Possibility to apply GlyDH-based biosensors for detection of glycerol and triglycerides in real wine samples was shown.

Keywords: PQQ; Quinoproteins; Biosensor; Glycerol dehydrogenase; Bioelectrochemistry

NIR spectrometry for counterfeit drug detection by Oxana Ye. Rodionova; Lars P. Houm�ller; Alexey L. Pomerantsev; Paul Geladi; James Burger; Vladimir L. Dorofeyev; Alexander P. Arzamastsev (pp. 151-158).

Express-methods for detection of counterfeit drugs are of vital necessity. Visual control, dissociating tests or simple color reaction tests reveal only very rough forgeries. The feasibility of information-rich NIR-measurements as an analytical method together with multivariate calibration for mathematical data processing for false drugs detection is demonstrated. Also, multivariate hyperspectral image analysis is applied providing additional diagnostic information. Hyperspectral imaging is becoming a useful diagnostic tool for identifying non-homogeneous spatial regions of drug formulation. Two types of drugs are used to demonstrate the applicability of these approaches.

Keywords: Counterfeit drugs; Near infra-red spectrometry; Hyperspectral image analysis; Multivariate classification

Quantitation of fusidane antibiotics in pharmaceuticals using the surfactant–dye binding degree method by Esther Mar�a Costi; Mar�a Dolores Sicilia; Soledad Rubio; Dolores P�rez-Bendito (pp. 159-165).

The determination of fusidic acid (FA)/sodium fusidate (SF) in dosage forms based on their modification of the binding degree of the cationic surfactant didodecyldimethylammonium bromide (DDABr) to the anionic dye Coomassie Brilliant Blue G (CBBG) was proposed. The formation of mixed DDABr–CBBG aggregates was monitored from changes in the spectral features of the dye. Addition of fusidane antibiotic to DDABr–CBBG aqueous mixtures caused a decrease in the surfactant–dye binding degree as a result of the formation of DDABr–drug aggregates. At the working pH (7.0), FA and SF were as fusidate anion; therefore, both hydrophobic and attractive electrostatic interactions were responsible for the formation of these mixed surfactant–drug aggregates. Based on the mathematical expression previously derived for determining surfactants, a linear calibration in the fusidane antibiotic concentration range 1.9–70mgL⁻¹ was obtained. The surfactant to dye binding degree (SDBD) method offered important advantages over conventional method used for quality control of fusidane antibiotics in terms of sensitivity (detection limit=0.6mgL⁻¹), selectivity, which permitted a minimum sample treatment (only dissolution of dosage forms), precision [relative standard deviations for the whole analytical process=1.5–2.0% ( n=6)], rapidity, because of the speed of both sample treatment and determination step, required instrumentation (a photometric titrator) and cost. Pharmaceutical samples analyzed included tablets, pomades and creams.

Keywords: Fusidane; Surfactant; Mixed aggregate; Fusidane antibiotics; Dye-surfactant and drug-surfactant binding degree

Classification of PDO olive oils on the basis of their sterol composition by multivariate analysis by M. Rui Alves; Sara C. Cunha; Joana S. Amaral; J.A. Pereira; M. Beatriz Oliveira (pp. 166-178).

The sterol compositions (GLC/FID/capillary column) of monovarietal olive oils (51 samples) from the most important cultivars of northeastern Portugal (Cvs. Cobrançosa, Madural and Verdeal Transmontana) and 27 commercial samples of olive oils with protected denomination of origin (PDO) from the same region and cultivars were evaluated.β-sitosterol, Δ⁵-avenasterol and campesterol were the most representative sterols. Cholesterol, stigmasterol, clerosterol and Δ⁷-stigmastenol were also found in all samples. All studied samples respected EC Regulation N. 2568, and in all cases total sterols were remarkably higher than the minimum limit set by legislation, ranging from 2003 to 2682mg/kg.Results were analysed with the help of several statistical techniques, including reduction of dimensionality by principal component analysis with cross-validation of the number of components, followed by the use of canonical variate predictive biplots for model development and canonical variate interpolative biplots for approximate classification of monovarietal and PDO olive oils. These biplots proved to be a very interesting solution in the present case study, overcoming the problems of interpretation and classification that arise whenever different multivariate analyses are coupled together.

Keywords: Sterols; Olive oils; Multivariate analysis; Biplots

Predicting bulk ambient aerosol compositions from ATOFMS data with ART-2a and multivariate analysis by Weixiang Zhao; Philip K. Hopke; Xueying Qin; Kimberly A. Prather (pp. 179-187).

The aerosol time-of-flight mass spectrometry (ATOFMS) has not generally been used to provide a quantitative estimation of chemical compositions of ambient aerosols. In an initial study, the possibility of developing a calibration model to predict chemical compositions from ATOFMS data was demonstrated, but because of the limited number of samples (only 12), the ability of the calibration model was not fully realized. In this study, 50 samples were created to further test the prediction ability of the calibration model. The conceptual framework is to relate the mass concentrations of the particles in the identified classes to the average aerosol compositions for each sampling time interval using a calibration model based on ART-2a and multivariate analysis. There may be some non-linearity between cluster mass concentrations and ambient species concentrations because of measurement errors, the scaling equations used to estimate particle mass and various assumptions required for building the model. Thus, in this study, PLS regression was integrated with radial basis functions (RBF-PLS) to obtain better prediction effects and compared to partial least square (PLS) regression alone. Compared with an earlier study, these results provide better and a more convincing demonstration of the ability of the calibration model to estimate the chemical compositions from ATOFMS data. The results also suggest that the model would be able to provide carbon data and thus substitute for thermal optical reflectance (TOR) measurements. Additionally, the calibration model based on RBF-PLS showed more accurate predictions in the cases with some non-linearity. Some of the key steps in the modeling effect are also discussed in detail.

Keywords: ATOFMS; Aerosol; Calibration model; Adaptive resonance theory; Aritificial neural networks; ART-2a; Partial least squares; PLS; Radial basis functions; RBF

Determination of²¹⁰Pb at ultra-trace levels in water by ICP-MS by D. Larivi�re; K.M. Reiber; R.D. Evans; R.J. Cornett (pp. 188-196).

²¹⁰Pb ( t_1/2=22.26 years) is one of the most difficult naturally occurring radionuclides to analyze directly via radiometric measurement due to its low-energy radioactive decay. In this work, inductively coupled plasma mass spectrometry (ICP-MS) was investigated as a possible alternative to radiometric counting for the determination of²¹⁰Pb. The formation of isobaric and polyatomic (molecular) interferences was studied and various strategies (i.e. co-precipitation, extraction chromatography, and derivatization) were tested to assess their usefulness in reducing these interferences. In addition, the potential of these strategies as pre-concentration methods was demonstrated. A²¹⁰Pb pre-concentration of >300-fold and recoveries of 63–73% were obtained using a combined co-precipitation and extraction chromatography protocol followed by derivatization using an ethylating reagent. The abundance sensitivity at m/ z=210 in the presence of stable Pb was also investigated for three types of mass spectrometers (sector-field (ICP-SFMS), quadrupole-based (ICP-QMS), and quadrupole-based with a dynamic reaction cell (ICP-QMS (DRC))). Finally, the method was applied to determine²¹⁰Pb in water samples and a detection limit of 90mBqL⁻¹ (10pgL⁻¹) was obtained.

Keywords: Pb-210; Radionuclide; Drinking water; ICP-MS; Polyatomic interferences

Comparison of EDXRF and ICP-OES after microwave digestion for element determination in plant specimens from an abandoned mining area by E. Margu�; I. Queralt; M.L. Carvalho; M. Hidalgo (pp. 197-204).

In this study an energy dispersive X-ray fluorescence (EDXRF) method has been applied to the analysis of some major and minor elements (K, Ca, Mn, Fe, Cu, Sr, Pb and Zn) in four higher plants growing on the waste landfills surrounding an abandoned Pb–Zn ore concentration factory.The validation of the procedure was performed by using a certified standard reference material (NIST SRM 1571: “Orchard leaves�? from National Institute of Standards and Technology) and by comparison with data obtained from two routine microwave assisted digestion procedures commonly applied to vegetation specimens (Dig A: HNO₃+H₂O₂, Dig B: HNO₃+H₂O₂+HF) plus ICP-OES.No statistically significant differences at the 98% confidence level were found between EDXRF and Dig A results, concerning to Ca, Pb, Sr and Zn. On the contrary, statistically significant differences were found for K, Mn, Fe and Cu due to the presence of a silica residue. The addition of HF (Dig B) neither accomplishes the solubilization of these elements. After Dig B a solid residue is formed mainly composed by Ca and F, according to the results obtained by scanning electronic microscopy (SEM).Taking into account all these facts, the EDXRF method proposed proved to be an effective tool for metal determination in vegetation specimens since it allows obviating the matrix destruction stage and the poor recoveries for some elements.

Keywords: Vegetation specimens; Microwave assisted digestion; EDXRF; ICP-OES; Mining wastes

A simple method for correcting the neutron self-shielding effect of matrix and improving the analytical response in prompt gamma-ray neutron activation analysis by K. Sudarshan; R. Tripathi; A.G.C. Nair; R. Acharya; A.V.R. Reddy; A. Goswami (pp. 205-211).

A simple method using an internal standard is proposed to correct for the self-shielding effect of B, Cd and Gd in a matrix. This would increase the linear dynamic range of PGNAA in analyzing samples containing these elements. The method is validated by analyzing synthetic samples containing large amounts of B, Cd, Hg and Gd, the elements having high neutron absorption cross-section, in aqueous solutions and solid forms. A simple Monte-Carlo simulation to find the extent of self-shielding in the matrix is presented. The method is applied to the analysis of titanium boride alloy containing large amount of boron. The satisfactory results obtained showed the efficacy of the method of correcting for the self-shielding effects in the sample.

Keywords: Prompt gamma-ray neutron activation analysis; Self-shielding correction; Internal mono-standard method

Analytical study for the charge-transfer complexes of losartan potassium by Ibrahim A. Darwish (pp. 212-220).

Studies were carried out, for the first time, to investigate the charge-transfer reactions of losartan potassium (LOS-K) as n-electron donor with the σ-acceptor iodine and various π-acceptors: 7,7,8,8-tetracyanoquinodimethane, 1,3,5-trinitrobenzene, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, p-chloranilic acid, tetracyanoethylene, 2,3,5,6-tetrabromo-1,4-benzoquinone, 2,3,5,6-tetrachloro-1,4-benzoquinone, and 2,4,7-trinitro-9-fluorenone. Different colored charge-transfer complexes and radical anions were obtained. Different variables affecting the reactions were studied and optimized. The formed complexes and the site of interaction were examined by UV–vis, IR, and¹H NMR techniques, and computational molecular modeling. The formation of the colored complexes were utilized in the development of simple, rapid and accurate spectrophotometric methods for the analysis of LOS-K in pure form as well as in its pharmaceutical tablets. Under the optimum reaction conditions, linear relationships with good correlation coefficients (0.9985–0.9998) were found between the absorbances and the concentrations of LOS-K in the range of 2–200μgml⁻¹. The limits of assays detection ranged from 0.61 to 19.65μgml⁻¹. No interference could be observed from the co-formulated hydrochlorothiazide (HCTZ), as well as from the additives commonly present in the tablets. The methods were successfully applied to the analysis of tablets from different manufacturers that contain LOS-K, alone or combined with HCTZ, with good accuracy and precision; the recovery percentages ranged from 98.96±1.62% to 101.58±1.29%. The results were compared favourably with the reported method.

Keywords: Losartan potassium; Charge-transfer complexes; Spectrophotometry; Pharmaceutical analysis

Author Index (pp. 221-223).

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Analytica Chimica Acta (v.549, #1-2)