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Analytica Chimica Acta (v.553, #1-2)

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

Contents (pp. v-vi).

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

Sensitive and selective liquid chromatography–tandem mass spectrometry method for the quantification of azithromycin in human plasma by Ramakrishna V.S. Nirogi; Vishwottam N. Kandikere; Manoj Shukla; Koteshwara Mudigonda; Santosh Maurya; Ravikumar Boosi; Anjaneyulu Yerramilli (pp. 1-8).

A simple, rapid, sensitive and selective liquid chromatography–tandem mass spectrometry method was developed and validated for the quantification of azithromycin, a broad-spectrum antimicrobial agent, in human plasma using erythromycin as internal standard. Following solid-phase extraction, the analytes were separated using an isocratic mobile phase on a reverse phase C₁₈ column and analyzed by mass spectrometry in the multiple reaction monitoring mode using the respective [M+H]⁺ ions, m/z 749/591 for azithromycin and m/z 734/576 for the IS. The assay exhibited a linear dynamic range of 5–500ng/mL for azithromycin in human plasma. The lower limit of quantification was 5ng/mL with a relative standard deviation of less than 5%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 2.0min for each sample made it possible to analyze more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.

Keywords: Azithromycin; Liquid chromatography–tandem mass spectrometry; Human plasma; Pharmacokinetic study

Peptides analysis in blood plasma using on-line system of supported liquid membrane and high-performance liquid chromatography by Anna Drapała; Jan Åke Jönsson; Piotr Wieczorek (pp. 9-14).

The potential of using supported liquid membrane (SLM) technique, combined with reversed-phase high-performance liquid chromatography (RP-HPLC) has been investigated for the determination of peptides in human blood plasma. The peptides studied were_DLLeu_DLPhe, MetLeuPhe, GlyLeuTyr and ValGluProIleProTyr. The carrier (Aliquat 336) was incorporated in membrane phase in order to facilitate the transport of investigated peptides. After extraction, the analyte-enriched acceptor phase was directly injected into an HPLC system for analysis. With SLM, high selectivity and efficiency were achieved for extraction of peptides in aqueous solutions. Lower extraction efficiency was obtained in plasma sample. The limiting factors were the presence of salts and proteins in blood plasma. The necessary of ultrafiltration application before the SLM was required in order to improve its stability. The minimum quantifiable concentration was 90–130ng/ml of the investigated peptides based on 0.5ml plasma. The standard curve was linear over the concentration range of 0.05–10μg/ml.

Keywords: Peptides; Supported liquid membrane; HPLC; Aliquat 336; Blood plasma

Determination of methacycline in human plasma by liquid chromatography coupled to tandem mass spectrometry by Xiaoyan Chen; Shuang Ren; Fang Meng; Yifan Zhang; Dafang Zhong (pp. 15-20).

A rapid, sensitive and selective LC–MS–MS method has been developed and validated for the determination of methacycline in human plasma and employed in a bioequivalence study of two 300mg tablet formulations in 18 healthy volunteers. The analyte and internal standard (IS) oxytetracycline were extracted from plasma using solid-phase extraction (SPE), then separated on a Diamonsil C₁₈ column using a mobile phase of methanol–water–formic acid (80:20:0.5, v/v/v). The detection was performed on a tandem mass spectrometer equipped with an electrospray ionization (ESI) source. Linearity was established in the concentration range of 5.0–4000ng/ml. The lower limit of quantification (LLOQ) was 5.0ng/ml. The intra- and inter-day relative standard deviation (R.S.D.) across three validation runs over the entire concentration range was <8.0%. Accuracy determined at three concentrations (5.0, 200 and 3600ng/ml for methacycline) ranged from 0.4 to 1.7% as terms of relative error (R.E.). Each plasma sample was chromatographed within 3.6min. The method is proved to be highly selective and suitable for bioequivalence evaluation of different formulations containing methacycline and clinical pharmacokinetic investigation of methacycline.

Keywords: Keyword; Methacycline

Multiresidue determination of nicotinoid insecticide residues in drinking water by liquid chromatography with electrospray ionization mass spectrometry by Serenella Seccia; Paola Fidente; Danilo Attard Barbini; Patrizia Morrica (pp. 21-26).

A multianalyte method has been developed for the confirmation and quantification of four neonicotinoids, acetamiprid, imidacloprid, thiacloprid and thiamethoxam in drinking water. These insecticides were extracted from water by solid-phase extraction (SPE) LiChrolut EN. Analytes’ determination and quantification were performed by liquid chromatography–mass spectrometry (LC–MS). Extraction efficiency experiments demonstrated the ability of this method to extract nicotinoids from water samples. Confirmatory analysis was carried out by LC-electrospray ionization–mass spectrometry (LC-ESI–MS) instrumentation equipped with a single-quadrupole mass filter. MS data acquisition was performed by two-ion selected ion monitoring (SIM) program. Average recoveries of the four analytes from drinking water samples were in the range of 95 and 104% with relative standard deviations (R.S.D.)<20%. The limit of quantification (LOQ) for each of the four insecticides was 0.03μgL⁻¹.

Keywords: Nicotinoid insecticides; LC-ESI–MS; SPE; Drinking water

Solvent enhanced ion chromatography of alkaline earth and transition metal ions on porous monolithic silica by Edel Sugrue; Pavel N. Nesterenko; Brett Paull (pp. 27-35).

The high-performance separation of alkaline earth and transition metal ions on a bare porous silica 10.0cm×0.46cm monolith (Merck Chromolith Si) was achieved using solvent enhanced ion chromatography. Using acetonitrile or methanol based ammonium and sodium acetate buffered mobile phases, the effect upon cation retention of mobile phase ionic strength, organic content and pH were evaluated. Increasing mobile phase acetonitrile concentration from 60 to 80% acetonitrile resulted in 10–15-fold increases in cation retention due to reduced hydration of the metal ions and hence enhanced ion-exchange interactions with surface silanol groups. The optimised conditions for the separation of Cu(II), Cd(II), Ni(II), Co(II) and Mn(II) were found to be 80% MeCN with 10.3mM ammonium acetate (pH 4.6). Detection of transition metal ions was obtained using post-column reaction with 4-(2-pyridylazo) resorcinol and absorbance at 510nm. Under elevated flow conditions (up to 5mL/min), total runs times could be reduced to under 4min. Optimum peak efficiencies were seen at flow rates of between 1.5 and 2mL/min and were equivalent to an average efficiency of 25,000N/m.

Keywords: Monolithic silica; Alkaline earth metal ions; Transition metal ions; Solvent enhanced ion chromatography

Evaluation of impact of different antioxidants on stability of dietary folates during food sample preparation and storage of extracts prior to analysis by Johan D.M. Patring; Madelene S. Johansson; Elena Yazynina; Jelena A. Jastrebova (pp. 36-42).

A troublesome factor during folate analysis is the instability of folates, especially tetrahydrofolate. This investigation was therefore performed to evaluate the relative effectiveness of four antioxidants (2-mercaptoethanol, dithiothreitol, 2,3-dimercapto-1-propanol, and 2-thiobarbituric acid) as stabilizing agents. The antioxidants were tested in the combination with 2% sodium ascorbate in acetate, phosphate, and HEPES/CHES buffers commonly used to extract folates from food samples. Baker's yeast was chosen as a model food matrix. A validated method based on reversed-phase high performance liquid chromatography with fluorescence and diode array detection was used for folate analysis. We showed that sample handling was of critical importance in folate analysis. Heat treatment, long-term storage, and repeated freeze/thaw cycles could impair the stability of tetrahydrofolate in varying degrees depending on buffers and antioxidants used. 2,3-Dimercapto-1-propanol was better than 2-mercaptoethanol in protecting tetrahydrofolate under heat extraction, long-term storage of food extracts and freezing/thawing. The use of 2,3-dimercapto-1-propanol as stabilizing agent in folate analysis may, therefore, be preferable owing to its lower toxicity and higher protective effectiveness. Preparation of food samples should include as few freeze/thaw steps as possible before analysis to prevent degradation of tetrahydrofolate.

Keywords: Folate analysis; Stability; Sample pre-treatment; Storage; Freezing/thawing; Antioxidant

Enantioseparation of chiral epoxides using four new cyclodextrin derivatives as chiral stationary phases of capillary gas chromatography by Xueyan Shi; Hongchao Guo; Min Wang (pp. 43-49).

Four new cyclodextrin derivatives (CDs), 2,6-di- O-benzyl-3- O-heptanonyl-β-cyclodextrin, 2,6-di- O-benzyl-3- O-octanonyl-β-cyclodextrin, 2,3-di- O-benzyl-6- O-heptanonyl-β-cyclodextrin, and 2,3-di- O-benzyl-6- O-octanonyl-β-cyclodextrin, were synthesized and used as chiral stationary phases for capillary gas chromatography (CGC). The four CDs can be divided into two groups by different substitution position of acyl groups in CD. It was found that both CDs with acyl groups in 6-position of CD and CDs with acyl groups in 3-position of CD possessed enantioselectivity to chiral epoxides though more baseline resolving were obtained on CDs with acyl groups in 3-position of CD than on CDs with acyl groups in 6-position of CD. On these CDs, enantiomers of chiral epoxides were successfully separated, and enantiomer excesses (e.e.%) of some chiral epoxides were also determined.

Keywords: Cyclodextrin derivatives; Chiral stationary phases; Capillary gas chromatography; Enantioseparation; Epoxides; Enantiomer excess

Determination of pyrethroid insecticide residues in vegetable oils by using combined solid-phases extraction and tandem mass spectrometry detection by Francesc A. Esteve-Turrillas; Agust�n Pastor; Miguel de la Guardia (pp. 50-57).

A methodology has been developed for the determination of pyrethroid insecticide residues in vegetable oils, based in a solid-phase extraction (SPE) with combined solid supports phases. Several solid phases such as florisil, alumina, C₁₈ and graphitized carbon black were tested in order to minimize fat residues, being a combination of treated alumina and C₁₈ which provided the best results.Oil samples were partitioned with acetonitrile–hexane (1:1) and then eluted through a combined column packed with deactivated basic-alumina and C₁₈, employing the acetonitrile extract as elution solvent. Gas chromatography tandem mass spectrometry was used for determination.Tetramethrin, Bifenthrin, Phenothrin, λ-Cyhalothrin, Permethrin, Cyfluthrin, Cypermethrin, Flucythrinate, Esfenvalerate, Fluvalinate and Deltamethrin were studied. Limits of detection values ranging from 0.3 to 1.4ng/g and repeatability values from 4 to 13%, evaluated from the relative standard deviation of three analyses of samples spiked at 1ng/g, were obtained.Neither matrix effects nor interferences were observed employing the proposed treatment in olive oil analysis and recoveries at 25 and 100ng/g level varied from 104±2 to 91±9%. The method can be also used for other vegetable oils such as sunflower, corn and soybean.

Keywords: Pyrethroid; Residues; Vegetable oil; Solid-phase extraction; Alumina; C; ₁₈; Tandem mass

Precise determination of Sc in natural waters by neutron activation analysis coupled with preconcentration of Sc by Miho Nomura; Mayumi Sato; Hiroshi Amakawa; Yasuji Oura; Mitsuru Ebihara (pp. 58-63).

We have developed a precise method for determining Sc in natural water samples by preconcentration neutron activation analysis (PNAA) using a carrier-free radioactive nuclide (⁴⁷Sc) as a yield tracer. The separation of Sc from natural water samples was performed by iron precipitation technique followed by an anion exchange method, which enables more than 88% of Sc recovery.Blank samples indicated that the blank contribution was not negligible for determining Sc in natural samples. As for a surface seawater sample, blank corrections in raw data (real amount+blank) were 58–65% and 29% for the use of the normal polyethylene sheet and the high purity sheet, respectively, for sealing samples in neutron activation. However, the corrected data showed a good agreement irrespective of the polyethylene sheets.Our surface seawater Sc data (0.23–0.34ng/kg) were comparable or slightly higher than the previous data. On the other hand, the rainwater Sc data (2.49–3.05ng/kg) were one order lower than the reported data. As for rainwater, we are confident that our data were more reliable than the reported data, because the reported data were considered to be susceptible to contamination. Although further studies are required, we believe our newly developed Sc determination technique could be applied to various natural water samples.

Keywords: Neutron activation analysis; Carrier-free radioactive nuclide; Yield tracer; Preconcentration; Seawater; Rainwater

Application of electrospray ionization-mass spectrometry to screen extractants for determination of insulin in an emulsion system by HPLC-UV by Yong Luo; Kaixun Huang; Huibi Xu (pp. 64-72).

Soybean lecithin and phenol intensely interfered in the determination of insulin with HPLC-UV in an emulsion system which was developed for transmucosal delivery. Thus, in this study electrospray ionization mass spectrometry (ESI-MS) with ion trap detection was applied to screen extractants to remove soybean lecithin and phenol in an insulin-loaded emulsion system (IES). The results showed that n-pentanol was a suited extractant to meet the measurement requests because a large quantity of soybean lecithin and phenol were removed simultaneously, and there appeared no interferences brought by n-pentanol in insulin measurement. The analytical method was assessed by the criteria including linearity (linearity range: 1.05–7.34U/mL and correlation coefficient: 0.99936), accuracy (recoveries: 98.1–102.5%), within-day precision (R.S.D.: 0.5%, n=6), LOD (0.01U/mL), and LOQ (0.03U/mL), and exhibited high sensitivity and specificity, and considerable accuracy and precision on the determination of insulin in the emulsion system. The application of this method had been successfully performed to study the storage conditions of IES, and the results indicated that insulin in IES would be stable at 4°C in light proof condition, which was significant for further pharmaceutical research.

Keywords: ESI-MS; Screening extractants; Insulin; Emulsion system; HPLC

New poly( N-(hydroxymethyl)methacrylamide–1-allyl-2-thiourea) hydrogels prepared by radiation-induced polymerisation: Selective adsorption, recovery and pre-concentration of Pt(II) and Pd(II) by Serhat Döker; Savaş Malcı; Mehmet Doğan; Bekir Salih (pp. 73-82).

Poly( N-(hydroxymethyl)methacrylamide–1-allyl-2-thiourea) hydrogels, poly(NHMMA–ATU), which have highly open pore size and high swellability, were synthesized by gamma irradiation using⁶⁰Co-γ source at different radiation dose rates and in different 1-allyl-2-thiourea content in the ternary mixture of NHMMA–ATU–H₂O. These hydrogels were used for specific platinum and palladium selectivity, recovery and pre-concentration from single and competitive media. It was observed that platinum and palladium adsorption capacities onto the hydrogels were also high at low pHs. Adsorption capacity of the hydrogels for platinum and palladium ions in acidic media around pH 0.5 were found to be about 477 and 407mgg⁻¹ dry hydrogels for Pt(II) and Pd(II). Adsorption of platinum and palladium ions onto the hydrogels was found to be very fast and also these hydrogels were showed extremely high selectivity to the platinum and palladium ions at pH 0.5 beside the extremely high concentration of the other transition and toxic metal ions. All matrix effects were easily eliminated adsorbing platinum and palladium ions onto the hydrogels at around pH 0.5 and desorbing into 3.0M HCl solution containing 0.8M thiourea because of the high specificity of these hydrogels to precious metal ions although the existing of the other metal ions at high concentration and at low pHs. Different amount of platinum spiked geological samples were analyzed for the method validation after discovered method applied and it was found that recovery of platinum was not less than 96.8%.

Keywords: Hydrogels; γ-Radiation; Recovery; Precious metal; Selectivity; Matrix elimination

Chromatographic prefractionation prior to two-dimensional electrophoresis and mass spectrometry identifies: Application to the complex proteome analysis in rat liver by Ming-xia Gao; Jin Hong; Peng-yuan Yang; Xing-min Zhang (pp. 83-92).

In this paper, we describe an approach for fractionating complex protein samples from rat liver prior to two-dimensional gel electrophoresis (2-DE) using reversed-phase high-performance liquid chromatography (RP-HPLC). The whole lysate of liver tissue was prefractionated by RP-HPLC with an optimal multi-stage linear gradient elution. Successive fractions were analyzed using 2-DE and selected spots were identified by MALDI-TOF-TOF mass spectrometry. The reproducibility of this prefractionation technology allows pooling of several consecutive runs of the same sample, resulting in a highly enrichment of low abundance proteins. Computer-assisted calculation showed that the total spot number of samples prefractionated by RP-HPLC was nearly five times as many as that of unfractionated sample. The choice of Coomassie Blue staining rather than silver staining indicated that RP-HPLC prefractionation can provide strong enrichment effect which enabled us to visualize additional and less abundance proteins. Chromatographic enrichment was also demonstrated by the peptide mass fingerprint data, which gave mass spectra with increased number of peptide detected and improved signal intensity.

Keywords: Reversed-phase high-performance liquid chromatography; Two-dimensional gel electrophoresis; Proteomics; MALDI-TOF-TOF

Determination of linear alkylbenzenesulfonates in water samples by immunoaffinity chromatography with fluorescence detection by M.L. S�nchez-Mart�nez; M.P. Aguilar-Caballos; S.A. Eremin; A. G�mez-Hens (pp. 93-98).

A simple and fast immunochromatographic method is proposed for the determination of linear alkylbenzenesulfonates (LASs) in real water samples. The approach consists of the injection in a commercial Protein G column of a preincubated mixture containing linear sodium 4-dodecylbenzenesulfonate (LDS), which was chosen as a LAS model, polyclonal anti-LAS antibodies, and a fluorescent tracer based on the coupling of a LAS mimic to a fluorescein derivative. This approach allows the separation of free and bound tracer fractions without any additional elution step, and the direct measurement of the fluorescence of the free tracer through the peak height of the immunochromatogram, which was proportional to the analyte concentration. The immunocolumn can be used up to 50 times without eluting and regenerated for at least 15 times. The dynamic range of the method is 0.09–3.0μgml⁻¹ LDS and the detection limit is 35ngml⁻¹. The precision, expressed as relative standard deviation, ranges between 5.4 and 7.1%. The application of the method to the analysis of water samples (tap-, ground- and waste-water) was carried out including a previous solid-phase extraction step that allowed to obtain a detection limit of 7ngml⁻¹, using 100ml of water sample. The range of the standard deviation obtained was 4–10 and the recoveries obtained for spiked samples ranged from 85.8 to 110.8%.

Keywords: Immunoaffinity chromatography; Fluorescence detection; LASs; Water samples

A fully automated method for in real time determination of laccase activity in wines by Manuel Urbano Cuadrado; Pedro M. P�rez-Juan; Mar�a D. Luque de Castro; Miguel A. G�mez-Nieto (pp. 99-104).

An automated method for determining laccase activity in musts and wines is here presented. The method is based on the Flow Injection technique using the mode of stop-flow at the detector with monitoring of the absorbance change caused by the oxidation of the substrate (syringaldazine). All the units that form the autoanalyser are controlled by a computer program for automating continuous processes developed by the authors. This work was aimed at providing wineries with a new tool for evaluating the degree of infection by Botrytis cinerea that overcomes the disadvantages involved in the determination of gluconic acid. In addition, a study of the relationship between the content of gluconic acid and laccase activity was carried out and no relationship was found. Thus, this acid is not an appropriate marker for evaluating infection by Botrytis. The analytical method was characterised and the limit of detection and limit of quantification were 0.2 and 0.6Uml⁻¹, respectively. The linear range was 0.6–24.0Uml⁻¹. This range is enough for the application of the method to wine; nevertheless, an enlargement of the range, if required, could be obtained with a higher dilution factor. Repeatability and reproducibility, expressed as relative standard deviation, were 4.0 and 6.5%, respectively. The total time necessary per analysis is 12min. The method can be used as a routine method at grape reception in wineries.

Keywords: Automation; Flow injection; Laccase; Wine

New insight on ancient cosmetic preparation by synchrotron-based infrared microscopy by M. Cotte; P. Dumas; G. Richard; R. Breniaux; Ph. Walter (pp. 105-110).

Synchrotron IR micro-spectroscopy is appropriately suited to the analysis of small particles of archaeological cosmetics. The sample originates from a 33 centuries old Egyptian cosmetic remain. Thanks to the high spectral quality and high lateral resolution achieved by this synchrotron-based microspectroscopic tool, new insights into the composition and spatial location of both organic and mineral components of the sample were obtained. Five different particles were analyzed and delivered similar findings: the core is fat rich, and surrounded with a mineral phase. In two particles, lead palmitate was clearly identified as a major component. Phosgenite (Pb₂CO₃Cl₂), a lead salt synthesized in aqueous solution, was also located in region near the surface of the particles.

Keywords: Synchrotron; FTIR; Microscopy; Cosmetic; Archaeology; Ancient

Multivariate calibration applied to the field of cultural heritage: Analysis of the pigments on the surface of a painting by Emilio Marengo; Maria Cristina Liparota; Elisa Robotti; Marco Bobba (pp. 111-122).

This paper concerns a first attempt of application of multivariate calibration to the field of cultural heritage for the determination of the superficial pigments composition of a painting. For this purpose, 10 mixtures of three organic pigments (Alizarin, Permanent Red and Phtalocyanine Green) selected by an augmented simplex-centroid design were mixed with linseed oil and spread on 10 cotton canvas strips. Each sample was characterised with three genuine replicates of an ATR-IR spectrum.Three calibration models, responding to the relative concentration of each specific pigment in the mixtures, were built with the partial least squares (PLS1) algorithm, using the ATR-IR spectra of the surfaces as predictors. The three mixtures corresponding to the augmentation of the simplex-centroid design were used to validate the model predictive ability which proved to be very satisfactory, with very low root mean squared error of prediction (RMSEP). Finally the models were successfully applied to a real painting, to predict the concentrations of some unknown mixtures of the three studied pigments.This work might have possible applications in the determination of the composition of dyes in real paintings to obtain information on the execution technique and for restoration purposes.

Keywords: Augmented simplex-centroid design; ATR-FT-IR spectroscopy; PLS (partial last squares); Cultural heritage

Flow injection chemiluminescence determination of cephalosporins in pharmaceutical preparations using tris (2,2′-bipyridyl) ruthenium (II)-potassium permanganate system by Chalermporn Thongpoon; Boonsom Liawruangrath; Saisunee Liawruangrath; R. Alan Wheatley; Alan Townshend (pp. 123-133).

A flow injection (FI) method using the tris(2,2′-bipyridyl) ruthenium(II) [Ru(bpy)₃²⁺]-potassium permanganate chemiluminescence(CL) was developed for the rapid and sensitive determination of cephalosporins such as cefoxitin, cefazolin, cephalexin, cefadroxil, cefaclor and cefoperazone. The method is based on the CL reaction of cephalosporins and Ru(bpy)₃²⁺ with potassium permanganate in the presence of perchloric acid, catalyzed by Mn(II). Under the optimum conditions, the calibration curves are linear over the range 0.10–12.0μgml⁻¹ for cefoxitin, 0.10–10.0μgml⁻¹ for cefoperazone and 0.10–15.0μgml⁻¹ for cefazolin, cephalexin, cefadroxil, and cefaclor, respectively. The limits of detection (3 σ) are 0.03μgml⁻¹ for cefoxitin and cefadroxil, 0.06μgml⁻¹ for cefoperazone and 0.08μgml⁻¹ for cefazolin, cephalexin and cefaclor, respectively. The method was successfully applied to the determination of cefoxitin, cefazolin, cephalexin and cefadroxil in pharmaceutical formulations with a sample throughput of 90h⁻¹. There were no interference effects from some common excipients used in pharmaceutical preparations.

Keywords: Flow injection; Chemiluminescence; Cephalosporins; Tris(2,2′-bipyridyl) ruthenium (II); Potassium permanganate; Pharmaceuticals

The use of the autocorrelation function in modeling of multivariate data by C.E. Alciaturi; M.E. Escobar; I. Est�ves (pp. 134-140).

The use of the autocorrelation function ( R₁) with lag 1 in univariate and multivariate model selection is proposed. In the univariate case, a Z-value is calculated from the R₁ of the residual vector. A high positive value of Z indicates the presence of smooth, non-random variations in the data not explained by the model considered. In the multivariate case, a new procedure is proposed. A “short�? path is found in the independent variable space, and the Z from the dependent variable residual vector is used to measure the smoothness of the changes in the dependent variable. Applications are shown for variable selection and determination of the number of latent variables in PLS1 models.

Keywords: Autocorrelation; Smoothness; Model selection; Linear models

Application of partial least-squares spectrophotometric-multivariate calibration to the determination of 2- sec-butyl-4,6-dinitrophenol (dinoseb) and 2,6-dinitro- p-cresol in industrial and water samples containing hydrocarbons by Juan A. Arancibia; Gerardo Mart�nez Delfa; Carlos E. Boschetti; Graciela M. Escandar; Alejandro C. Olivieri (pp. 141-147).

The present report describes the spectrophotometric determination of 2- sec-butyl-4,6-dinitrophenol (dinoseb) and 2,6-dinitro- p-cresol, two inhibitors of the styrene polimerization, in two very different types of matrices. One of them is present in an industrial distillation tower, and contains styrene and more than 60 hydrocarbons. Partial least-squares (PLS) multivariate calibration enabled us to determine both analytes without the necessity of applying extraction processes, as well as significantly reducing the time involved in the currently applied analytical method. The limit of detection for both compounds, referred to the industrial sample, was 1.0μgml⁻¹, for concentration ranges of 0–261μgml⁻¹ (dinoseb) and 0–448μgml⁻¹ (2,6-dinitro- p-cresol). The method was successfully applied to real samples. In addition, dinoseb was simultaneously determined with 2,6-dinitro- p-cresol in hydrocarbon–water mixtures by PLS calibration. In this type of samples, the concentrations are significantly lower and thus a pre-concentration step through solid-phase extraction preceded the spectrophotometric measurements. The limits of detection for the simultaneous determination of dinoseb and 2,6-dinitro- p-cresol were 1.2 and 1.0ngml⁻¹, respectively.

Keywords: Spectrophotometry; Multivariate calibration; Partial least-squares; Solid-phase extraction; 2-; Sec; -butyl-4,6-dinitrophenol; 2,6-Dinitro-; p; -cresol

Surface detection of chemical warfare agent simulants and degradation products by Abu B. Kanu; Paul E. Haigh; Herbert H. Hill (pp. 148-159).

Chemical warfare agent (CWA) simulants as well as their degradation and hydrolysis products were detected from surfaces using thermal desorption ion mobility spectrometry (TD-IMS). CWA simulant materials that closely mimic the chemical structures of real CWA G/V-type nerve and S-type vesicant simulants were used in this study. Reduced mobility constants ( K₀) in air were reported for 20 compounds studied. Spectra for sample materials as low as 1ng deposited on a paper filter were produced for most of the compounds. Detection limits as low as 15pg of sample material with a sensitivity of 3.2×10² ampere per gram (Ag⁻¹) were reported. TD-IMS, which is normally used for the detection of explosives and drugs of abuse, demonstrated the capability of separating and detecting mixtures of CWA simulants, degradation and hydrolysis products from surface samples. TD-IMS demonstrated clear advantages of speed, high throughput and versatility over chromatographic methods of analysis for detecting CWA simulants, degradation and hydrolysis products. Successful development of the technique may lead to a practical and simple sensor for CWA and related compounds that could be installed and used at sensitive locations around the USA and throughout the world.

Keywords: Chemical warfare agent simulants; Degradation products; Thermal desorption ion mobility spectrometry; Surface detection; Sensors

Ion-selective electrodes: polyaniline modification and anion recognition (pp. 160-168).

Highly selective single-use fluoride ion optical sensor based on aluminum(III)-salen complex in thin polymeric film by Ibrahim H.A. Badr; Mark E. Meyerhoff (pp. 169-176).

A highly selective optical sensor for fluoride ion based on the use of an aluminum(III)-salen complex as an ionophore within a thin polymeric film is described. The sensor is prepared by embedding the aluminum(III)-salen ionophore and a suitable lipophilic pH-sensitive indicator (ETH-7075) in a plasticized poly(vinyl chloride) (PVC) film. Optical response to fluoride occurs due to fluoride extraction into the polymer via formation of a strong complex with the aluminum(III)-salen species. Co-extraction of protons occurs simultaneously, with protonation of the indicator dye yielding the optical response at 529nm. Films prepared using dioctylsebacate (DOS) are shown to exhibit better response (e.g., linear range, detection limit, and optical signal stability) compared to those prepared using ortho-nitrophenyloctyl ether ( o-NPOE). Films formulated with aluminum(III)-salen and ETH-7075 indicator in 2DOS:1PVC, exhibit a significantly enhanced selectivity for fluoride over a wide range of lipophilic anions including salicylate, perchlorate, nitrate, and thiocyanate. The optimized films exhibit a sub-micromolar detection limit, using glycine-phosphate buffer, pH 3.00, as the test sample. The response times of the fluoride optical sensing films are in the range of 1–10min depending on the fluoride ion concentration in the sample. The sensor exhibits very poor reversibility owing to a high co-extraction constant (log K=8.5±0.4), indicating that it can best be employed as a single-use transduction device. The utility of the aluminum(III)-salen based fluoride sensitive films as single-use sensors is demonstrated by casting polymeric films on the bottom of standard polypropylene microtiter plate wells (96wells/plate). The modified microtiter plate optode format sensors exhibit response characteristics comparable to the classical optode films cast on quartz slides. The modified microtiter is utilized for the analysis of fluoride in diluted anti-cavity fluoride rinse samples and the results obtained are shown to correlate well with the analysis performed using the LaF₃ single crystal ion-selective electrode.

Keywords: Fluoride ion sensor; Aluminum(III)-salen complex; pH-chromoionophore; Single-use optical sensors; Microtiter plate format optode

Ni(II)-selective ion sensors of salen type Schiff base chelates by A.K. Jain; V.K. Gupta; P.A. Ganeshpure; J.R. Raisoni (pp. 177-184).

The two nickel chelates of Schiff bases, N-(2-hydroxybenzyl)- N′-(2-hydroxybenzylidene)ethylenediamine Ni(II) (I) and N-(2-hydroxybenzylidene)- N′-(2-picolyl)ethylenediamine Ni(II) (II), have been synthesized and explored as a neutral ionophores for preparing polyvinyl chloride based membrane sensors selective to Nickel(II). The addition of sodium tetraphenylborate and various plasticizers, viz., DOS, TEHP, DEP and CN has been found to substantially improve the performance of the sensors. The best performance was obtained with the sensor having membrane of chelate (II) with composition (w/w) chelate (1%):PVC (33%):CN (65.5%):NaTPB (0.5%). This sensor exhibits Nernstian response in the concentration range 3.2×10⁻⁶ to 5.0×10⁻²M Ni(II), performs satisfactorily over wide pH range of (2.2–5.9) with a fast response time (∼10s). The sensor was also found to work satisfactorily in partially non-aqueous media up to 25% (v/v) content of acetone, methanol or ethanol and could be used over a period of 4 months. The response of the sensor was highly selective to Ni²⁺ over a large number of cations and it could therefore be used for Ni²⁺ estimation in the presence of a number of interfering ions. The sensor could be used successfully for the estimation of nickel at trace level in biological and environmental samples.

Keywords: Schiff base chelate; PVC membrane; Nickel selective sensor

Designing an arsenate-selective sensor based on the bis(dichloroorganostannyl)methane derivative [Cl₂(4- n-C₈H₁₇-C₆H₄)Sn]₂CH₂ by Nikos A. Chaniotakis; Klaus Jurkschat; Gregor Reeske; Antonis Volosirakis (pp. 185-189).

A new lipophilic bicentric organotin arsenate-selective carrier is reported. This new bis(dichloro-4- n-octylphenylstannyl)methane carrier is used for the construction and optimization of an arsenate-selective electrode. The liquid polymeric membrane of the arsenate-selective electrode was optimized and the resulting electrode shows a very good selectivity [KH2AsO4−,Xpot X: ClO₄⁻ (0.87)>AsO₄⁻ (0)>H₂PO₄⁻ (−0.97)>NO₃⁻ (−1.24)>Cl⁻ (−1.61)>SO₄²⁻ (−3.16)] and a detection limit in the order of 2×10⁻⁶M, in a glutamic buffer of pH 4.0. This study sets the grounds for the development of an ionophore-based sensor for the direct and selective determination of arsenate in aqueous samples.

Keywords: Sensor; Ionophor; Arsenate; Lewis acid; Tin

Impedance immunosensor based on receptor protein adsorbed directly on porous gold film by Zhaopeng Chen; Jianhui Jiang; Guoli Shen; Ruqin Yu (pp. 190-195).

In this paper, a new immunosensor has been proposed based on the receptor protein adsorbed directly on a porous gold film. The film was produced electrochemically on a glassy carbon electrode in 0.08M hydrogen tetrachloroaurate solution containing 0.004M lead acetate with applied potential of −0.5V (versus Ag/AgCl) for 50s. The assay was carried out based on a sandwich procedure. The impedance signals amplified by precipitation of an insoluble product on the electrode showed good linearity with the content of IgG in the range of 0.011–11ngmL⁻¹ with a detection limit of 0.009ngmL⁻¹. The gold film was characterized by scanning electron microscopy and the results showed porous gold nanoclusters were electrochemically deposited on the glassy carbon electrode.

Keywords: Immunosensor; Porous gold film; Adsorption; Faradaic impedance spectroscopy

A one-step method to construct a third-generation biosensor based on horseradish peroxidase and gold nanoparticles embedded in silica sol–gel network on gold modified electrode by Junwei Di; Chunping Shen; Shaohua Peng; Yifeng Tu; Shujin Li (pp. 196-200).

A one-step method for fabrication of horseradish peroxidase (HRP) biosensor has been developed. The gold nanoparticles and HRP were simultaneously embedded in silica sol–gel network on gold electrode surface in the presence of cysteine. The immobilized HRP exhibited direct electrochemical behavior toward the reduction of hydrogen peroxide. The heterogeneous electron transfer rate constant was evaluated to be 7.8s⁻¹. The biosensor displayed an excellent elctrocatalytic response to the reduction of H₂O₂ without any mediator. The calibration range of H₂O₂ was from 1.6μmolL⁻¹ to 3.2mmolL⁻¹ and a detection limit of 0.5μmolL⁻¹ at a signal-to-noise ratio of 3. TheKMapp value of HRP immobilized on the electrode surface was found to be 1.1mmolL⁻¹. The biosensor exhibited high sensitivity, rapid response and long-term stability.

Keywords: Horseradish peroxidase; Direct electron transfer; Gold nanoparticles; Silica sol–gel; Biosensor

Anodic stripping voltammetric determination of traces and ultratraces of thallium at a graphite microelectrode by Nadia Spano; Angelo Panzanelli; Paola Costantina Piu; Maria Itria Pilo; Gavino Sanna; Renato Seeber; Andrea Tapparo (pp. 201-207).

A bare graphite microelectrode was used for the anodic stripping voltammetry determination of traces and ultratraces of Tl⁺ ion in aqueous solutions at pH 3.5, in the presence of a 1×10⁻³molL⁻¹ EDTA solution. The proposed method, validated and tested at ultratrace level in environmental water samples, showed low detection and quantification limits (0.01 and 0.03μgL⁻¹, respectively) and excellent capability to determine the analyte also in the presence of a very high excess of interfering ions, i.e. 2200:1 and 10,000:1 (w:w) for Pb²⁺ and Cd²⁺, respectively. Furthermore, the wide linearity range, the absence of bias, the low time required for each measurement and the low cost of the instrumentation needed are additional factors supporting the application of such a method as a screening tool in the direct determination of thallium ionic species in environmental samples.

Keywords: Thallium; Square wave anodic stripping voltammetry; SWASV; Microelectrodes; Environmental samples

Multivariate optimization for molybdenum determination in environmental solid samples by slurry extraction-ETAAS by M. Felipe-Sotelo; M.J. Cal-Prieto; A. Carlosena; J.M. Andrade; E. Fern�ndez; D. Prada (pp. 208-213).

A direct procedure to determine molybdenum in environmental solid samples (coal fly ash, sediment, soil and urban dust) by slurry extraction-electrothermal atomic absorption spectroscopy (SE-ETAAS) employing multivariate optimization is presented. Sample mass, ultrasonic power, HNO₃ concentration and HCl concentration were the most important variables affecting the extraction of Mo, as Plackett–Burman designs put forward. Time of agitation revealed not significant (within the 10–100s range), thanks to the focused ultrasonic agitation program employed throughout (using a USS-100 probe). Two Simplex, a regular and a modified one, were carried out to simultaneously optimize the HNO₃ and HCl concentrations. Both Simplex converged to 14% (v/v) HCl and 10% (v/v) HNO₃. Sample mass was studied by means of a univariate procedure (optimum at 50mg). Furnace programs were studied using wall atomization with and without BaF₂ as modifier, yielding similar results. Quantitative extraction was obtained, with good accuracy (ca. 90% recovery) and precision (R.S.D.<9%), evaluated using five CRMs (coal fly ash SRM1633a, urban dust SRM1649a, marine sediments BCSS1 and PACS1, soil GBW07401). The limit of detection of the method was 0.1μgg⁻¹ (20mg/1mL slurry) and the characteristic mass was 9.5±1.7pg. Main advantages of the slurry extraction procedure are that it can be implemented directly on the autosampler cups, and that it is inexpensive and fast.

Keywords: Mo; Environmental solid samples; Slurry extraction-ETAAS; Multivariate optimization

Antimony speciation analysis in sediment reference materials using high-performance liquid chromatography coupled to hydride generation atomic fluorescence spectrometry by M. Potin-Gautier; F. Pannier; W. Quiroz; H. Pinochet; I. de Gregori (pp. 214-222).

This work presents the development of suitable methodologies for determination of the speciation of antimony in sediment reference samples. Liquid chromatography with a post-column photo-oxidation step and hydride generation atomic fluorescence spectrometry as detection system is applied to the separation and determination of Sb(III), Sb(V) and trimethylantimony species.Post-column decomposition and hydride generation steps were studied for sensitive detection with the AFS detector. This method was applied to investigate the conditions under which speciation analysis of antimony in sediment samples can be carried out. Stability studies of Sb species during the extraction processes of solid matrices, using different reagents solutions, were performed. Results demonstrate that for the extraction yield and the stability of Sb species in different marine sediment extracts, citric acid in ascorbic acid medium was the best extracting solution for antimony speciation analysis in this matrix (between 55% and 65% of total Sb was recovered from CRMs, Sb(III) being the predominant species). The developed method allows the separation of the three compounds within 6min with detection limits of 30ngg⁻¹ for Sb(III) and TMSbCl2 and 40ngg⁻¹ for Sb(V) in sediment samples.

Keywords: Speciation; Antimony; Extraction; Atomic fluorescence spectrometry; Hydride generation; Liquid chromatography; Sediment samples; Stability study

Author Index (pp. 223-224).

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Analytica Chimica Acta (v.553, #1-2)