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Analytica Chimica Acta (v.583, #1)

Editorial Board (pp. co1).

Contents (pp. v-vi).

Calendar of forthcoming meetings (pp. n1).

Contents (pp. v-vi).

Editorial Board (pp. co1).

Calendar of forthcoming meetings (pp. n1).

Publishers Note (pp. 1-1).

Ultrasound assistance to liquid–liquid extraction: A debatable analytical tool by M.D. Luque de Castro; F. Priego-Capote (pp. 2-9).

A review of the effects of ultrasound (US) on liquid–liquid extraction is here presented. The phenomena produced by US, particularly cavitation, influence in different ways mass transfer between two immiscible liquids. The nature of the donor and acceptor phases and the presence of a chemical reaction dramatically affect mass transfer. Discrete and continuous approaches for the development of US-assisted liquid–liquid extraction as well as their advantages and limitations are discussed as a function of the system under study. In depth research in this field is needed in order to establish the liquid–liquid systems which can benefit by application of this type of energy.

Keywords: Liquid–liquid extraction; Ultrasound; Liquid samples; Sample preparation; Acceleration; Automation

Ultrasound assistance to liquid–liquid extraction: A debatable analytical tool by M.D. Luque de Castro; F. Priego-Capote (pp. 2-9).

Keywords: Liquid–liquid extraction; Ultrasound; Liquid samples; Sample preparation; Acceleration; Automation

Measurement of nitrophenols in air samples by impinger sampling and supported liquid membrane micro-extraction by Edmund J. Bishop; Somenath Mitra (pp. 10-14).

A sensitive analytical technique for the detection of trace nitrophenols in air has been developed. The steps in this process are impinger sampling to capture the nitrophenols in an aqueous phase, which is then followed by supported liquid membrane micro-extraction (SLMME) and analytical detection. The nitrophenols were analyzed by reverse-phase high performance liquid chromatography (HPLC) and did not require any derivatization. Method detection limits (MDL) of 0.5–1.0ngL⁻¹ from aqueous solutions and 3.1–46.7ppbV from air extractions were observed. The high enrichment of nitrophenol in SLMME allowed low detection limits even with HPLC-UV detection. SLMME is an inexpensive, easy to use procedure that employs disposable membrane fibers.

Keywords: Membrane separation; Phenols; Liquid phase micro-extraction

Measurement of nitrophenols in air samples by impinger sampling and supported liquid membrane micro-extraction by Edmund J. Bishop; Somenath Mitra (pp. 10-14).

Keywords: Membrane separation; Phenols; Liquid phase micro-extraction

Experimental design for extraction and quantification of phenolic compounds and organic acids in white “Vinho Verde” grapes by M.S. Dopico-García; P. Valentão; L. Guerra; P.B. Andrade; R.M. Seabra (pp. 15-22).

An experimental design was applied for the optimization of extraction and clean-up processes of phenolic compounds and organic acids from white “Vinho Verde” grapes. The developed analytical method consisted in two steps: first a solid–liquid extraction of both phenolic compounds and organic acids and then a clean-up step using solid-phase extraction (SPE). Afterwards, phenolic compounds and organic acids were determined by high-performance liquid chromatography (HPLC) coupled to a diode array detector (DAD) and HPLC–UV, respectively. Plackett–Burman design was carried out to select the significant experimental parameters affecting both the extraction and the clean-up steps. The identified and quantified phenolic compounds were: quercetin-3- O-glucoside, quercetin-3- O-rutinoside, kaempferol-3- O-rutinoside, isorhamnetin-3- O-glucoside, quercetin, kaempferol and epicatechin. The determined organic acids were oxalic, citric, tartaric, malic, shikimic and fumaric acids. The obtained results showed that the most important variables were the temperature (40°C) and the solvent (acid water at pH 2 with 5% methanol) for the extraction step and the type of sorbent (C18 non end-capped) for the clean-up step.

Keywords: White grapes; Experimental design; Plackett–Burman; Phenolic compounds; Organic acids

Strain and phase identification of the U.S. category B agent Coxiella burnetii by matrix assisted laser desorption/ionization time-of-flight mass spectrometry and multivariate pattern recognition by Carrie Y. Pierce; John R. Barr; Adrian R. Woolfitt; Hercules Moura; Edward I. Shaw; Herbert A. Thompson; Robert F. Massung; Facundo M. Fernandez (pp. 23-31).

Accurate bacterial identification is important in diagnosing disease and in microbial forensics. Coxiella burnetii, a highly infective microorganism causative of the human disease Q fever, is now considered a U.S. category B potential bioterrorism agent. We report here an approach for the confirmatory identification of C. burnetii at the strain level which involves the combined use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and supervised pattern recognition via Partial Least Squares-Discriminant Analysis (PLS-DA). C. burnetii isolates investigated in this study included the following prototype strains from different geographical and/or historical origins and with different antigenic properties: Nine Mile I, Australian QD, M44, KAV, PAV, Henzerling, and Ohio. After culture and purification following standard protocols, linear MALDI-TOF mass spectra of pure bacterial cultures were acquired in positive ion mode. Mass spectral data were normalized, baseline-corrected, denoised, binarized and modeled by PLS-DA under crossvalidation conditions. Robustness with respect to uncontrolled variations in the sample preparation and MALDI analysis protocol was assessed by repeating the experiment on five different days spanning a period of 6 months. The method was validated by the prediction of unknown C. burnetii samples in an independent test set with 100% sensitivity and specificity for five out of six strain classes.

Keywords: Microorganism identification; Coxiella burnetii; Matrix-assisted laser desorption/ionization; Time-of-flight mass spectrometry; Partial least squares discriminant analysis

Development and application of immunoaffinity column chromatography for atrazine in complex sample media by Jane C. Chuang; Jeanette M. Van Emon; Randy Jones; Joyce Durnford; Robert A. Lordo (pp. 32-39).

A rabbit antibody immunoaffinity (IA) column procedure was evaluated as a cleanup method for the determination of atrazine in soil, sediment, and food. Four IA columns were prepared by immobilizing a polyclonal rabbit anti-atrazine antibody solution to HiTrap Sepharose columns. Atrazine was bound to the IA columns when the loading solvents were either 100% water, 2% acetonitrile in water, or 10% methanol in phosphate buffered saline (PBS). Quantitative removal of atrazine from the IA columns was achieved with elution solvents of either 70% ethanol in water, 70% methanol in water, or 100% methanol. One control column was prepared using nonspecific rabbit IgG antibody. This control column did not retain any applied atrazine indicating atrazine did not bind indiscriminately to protein or the Sepharose support. The four IA columns showed reproducible coupling efficiency for the immobilization of the atrazine antibody and consistent binding and releasing of atrazine. The coupling efficiency (4.25mg of antibody in 1mL of resin bed) for the four IA columns ranged from 93 to 97% with an average of 96±2% (2.1%). Recoveries of the 500, 50, and 5ngmL⁻¹ atrazine standard solutions from the four IA columns were 107±7% (6.5%), 122±14% (12%), and 114±9% (8.0%) respectively, based on enzyme-linked immunosorbent assay (ELISA) data. The maximum loading was approximately 700ng of atrazine for each IA column (∼0.16μg of atrazine per mg of antibody). The IA columns could withstand 100% methanol as the elution solvent and could be reused more than 50 times with no change in performance. The IA columns were challenged with soil, sediment, and duplicate-diet food samples and effectively removed interferences from these various matrices for subsequent gas chromatography/mass spectrometry (GC/MS) or ELISA analysis. The log-transformed ELISA and GC/MS data were significantly correlated for soil, sediment and food samples although the ELISA values were slightly higher than those obtained by GC/MS. The IA column cleanup procedure coupled with ELISA analysis could be used as an alternative effective analytical method for the determination of atrazine in complex sample media such as soil, sediment, and food samples.

Keywords: Immunoaffinity column; Atrazine; Soil; Sediment; Duplicate-diet food; Gas chromatography/mass spectrometry; Enzyme-linked immunosorbent assay; Immunoassay

A novel immunoassay based on the dissociation of immunocomplex and fluorescence quenching by gold nanoparticles by Zhaofeng Peng; Zhaopeng Chen; Jianhui Jiang; Xiaobing Zhang; Guoli Shen; Ruqin Yu (pp. 40-44).

This study reports a novel, simple and sensitive immunoassay using fluorescence quenching caused by gold nanoparticles coated with antibody. The method is based on a non-competitive heterogeneous immunoassay of human IgG conducted by the typical procedure of sandwich immunocomplex formation. Goat anti-human IgG was first adsorbed on polystyrene microwells, and human IgG analyte was captured by the primary antibody and then sandwiched by antibody labeled with gold nanoparticles. The sandwich-type immunocomplex was subsequently dissociated by the mixed solution of sodium hydroxide and trisodium citrate, the solution obtained, which contains gold nanoparticles coated with antibody, was used to quench fluorescence. The fluorescence intensity of fluorescein at 517nm was inversely proportional to the logarithm of the concentration of human IgG in the dynamic range of 10–5000ngmL⁻¹ with a detection limit of 4.7ngmL⁻¹. The electrochemical experiments and the UV–vis measurements were applied to demonstrate whether the immunoglod was dissociated completely and whether the gold nanoparticles aggregated after being dissociated, respectively. The proposed system can be extended to detect target molecules such as other kinds of antigen and DNA strands, and has broad potential applications in disease diagnosis.

Keywords: Immunoassay; Gold nanoparticles; Dissociation; Fluorescence quenching

An enzymatic method for the rapid measurement of the hemoglobin A_1c by a flow-injection system comprised of an electrochemical detector with a specific enzyme-reactor and a spectrophotometer by Yoko Nanjo; Ryuzo Hayashi; Toshio Yao (pp. 45-54).

A flow-injection analytical (FIA) system, comprised of an electrochemical detector with a fructosyl-peptide oxidase (FPOX-CET) reactor and a flow-type spectrophotometer, was proposed for the simultaneous measurement of glycohemoglobin and total hemoglobin in blood cell. The blood cell samples were hemolyzed with a surfactant and then treated with protease. In the first stage of operation, total hemoglobin in digested sample was determined spectrophotometrically. In the second stage, fructosyl valyl histidine (FVH) released from glycohemoglobin by the selective proteolysis was determined specifically using the electrochemical detector with the FPOX-CET reactor. The FIA system could be automatically processed at an analytical speed of 40 samples per hour. The proposed assay method could determine selectively only the glycated N-terminal residue of β-chain in glycohemoglobin and total hemoglobin in blood cell. The enzymatic hemoglobin A_1c (HbA_1c) value calculated by the concentration ratio of the FVH to total hemoglobin, was closely correlated with the HbA_1c values certified by the Japan Diabetic Society (JDS) and the International Federation of Clinical Chemistry (IFCC).

Keywords: Hemoglobin A; _1c; (HbA; _1c; ); Glycohemoglobin; Total hemoglobin; Diabetes; Enzymatic assay; Flow-injection analysis; Fructosyl-peptide oxidase; Protease

Direct determination of closely overlapping drug mixtures of diflunisal and salicylic acid in serum by means of derivative matrix isopotential synchronous fluorescence spectrometry by J.A. Murillo Pulgarín; A. Alañón Molina; P. Fernández López; I. Sánchez-Ferrer Robles (pp. 55-62).

A direct method for the simultaneous fluorimetric determination of two anti-inflammatory drugs in serum is proposed. The combination of matrix isopotential synchronous fluorescence (MISF) and first derivative technique provides good analytical results and permits the simultaneous determination of diflunisal and salicylic acid in human serum. MISF spectra are obtained by calculating the isopotential trajectory in the three-dimensional fluorescence spectrum for a serum solution. In the spectral contour, the trajectory is taken to be the portion of the line that passes by the fluorescence maxima of both compounds ensuring a sensitivity level similar to that of a direct determination in absence of background fluorescence. Analysis was carried out in water using a pH of 7.2 provides by 0.1M sodium dihydrogen phosphate buffer. Serum samples are diluted 100 times and provide linear calibration plots at diflunisal and salicylic acid concentrations up to 800ngmL⁻¹. The goodness of the analytical signal was checked by using variance analysis. Signals recorded throughout the calibration range were subjected to three calibrations per each analyte, both in the absence and in the presence of variable amounts of the other analyte. Differences between individual calibrations and slopes were compared with those within individual calibrations. Based on the results, diflunisal and salicylic acid can be accurately quantified in the presence of each other. The limit of detection calculated according to Clayton who uses error propagation throughout the calibration curve and a non-centralized security factor was 36.8 and 37.3ngmL⁻¹ for diflunisal and salicylic acid, respectively.

Keywords: Diflunisal; Salicylic acid; Serum; Isopotential fluorimetry

Determination of poorly fluorescent carbamate pesticides in water, bendiocarb and promecarb, using cyclodextrin nanocavities and related media by Natalia L. Pacioni; Alicia V. Veglia (pp. 63-71).

The effect of native cyclodextrins (α, β, or γCD with six, seven and eight glucose units, respectively), hydroxypropyl-β-cyclodextrin (HPCD), chitosan (CHT) and glucose in water solution or water with n-propylamine (PA) as co-solvent upon the UV–vis and fluorescence properties of poorly fluorescent N-methyl carbamates pesticides(C) as bendiocarb (2,2-dimethyl-1,3-benzodioxol-4-ol methylcarbamate,BC) and promecarb (3-methyl-5-(1-methylethyl)phenol methylcarbame,PC) was examined.Fluorescent enhancement was found for both substrates with all CDs in water or PA-water except fromPC with αCD. The addition of CHT increases the fluorescence ofBC but decreases the fluorescence ofPC, and glucose addition gives in both cases no spectral changes.Host-guest interaction was clearly determined by fluorescence enhancement with βCD and HPCD with a 1:1 stoichiometry for the complexes (C:CD). The values obtained for the association constants ( K_A, M⁻¹) were (6±2)×10² and (2.3±0.3)×10² forBC:βCD andBC:HPCD complexes, respectively. ForPC:βCD andPC:HPCD the values of K_A were (19±2)×10² and (21±2)×10², respectively. The ratio of the fluorescence quantum yields for the bound and free substrates ( ϕ^CCD/ ϕ^C) was in the range 1.74–3.8. The limits of detection ( L_D, μgmL⁻¹) for the best conditions were (0.57±0.02) forBC with HPCD and (0.091±0.002) forPC with βCD in water. Application to the analysis in pesticide spiked samples of tap water and fruit yields satisfactory apparent recoveries (84–114%), and for the extraction procedure in fruits and a commercial formulation, recoveries were of 81–98% and 104%, respectively. The method is rapid, simple, direct, sensitive and useful for pesticide analysis.

Keywords: Bendiocarb; Promecarb; Cyclodextrin nanocavities; Molecular nanosensor; Carbamate pesticides; Chitosan; Propylamine effects

Determination of poorly fluorescent carbamate pesticides in water, bendiocarb and promecarb, using cyclodextrin nanocavities and related media by Natalia L. Pacioni; Alicia V. Veglia (pp. 63-71).

Keywords: Bendiocarb; Promecarb; Cyclodextrin nanocavities; Molecular nanosensor; Carbamate pesticides; Chitosan; Propylamine effects

Sensitive and ultra-fast determination of arsenic(III) by gas-diffusion flow injection analysis with chemiluminescence detection by Cristina Lomonte; Matthew Currell; Richard J.S. Morrison; Ian D. McKelvie; Spas D. Kolev (pp. 72-77).

A novel chemiluminescence gas-diffusion flow injection system for the determination of arsenic(III) in aqueous samples is described. The analytical procedure involves injection of arsenic(III) samples and standards into a 0.3molL⁻¹ hydrochloric acid carrier stream which is merged with a reagent stream containing 0.2% (w/v) sodium borohydride and 0.015molL⁻¹ sodium hydroxide. Arsine, generated in the combined carrier/reagent donor stream, diffuses across the hydrophobic Teflon membrane of the gas-diffusion cell into an argon acceptor stream and then reacts with ozone in the flow-through chemiluminescence measuring cell of the flow system. Under optimal conditions, the method is characterized by a wide linear calibration range from 0.6μgL⁻¹ to 25mgL⁻¹, a detection limit of 0.6μgL⁻¹ and a sample throughput of 300 samples per hour at 25mgL⁻¹ and 450 samples per hour at 25μgL⁻¹.

Keywords: Gas-diffusion flow injection analysis; Chemiluminescence detection; Arsenic determination; Arsine; Ozone

Dimethylthioarsinic anhydride: A standard for arsenic speciation by Michael Fricke; Matthias Zeller; William Cullen; Mark Witkowski; John Creed (pp. 78-83).

Dimethylthioarsinic acid (DMTA^V) has recently been identified in biological, dietary and environmental matrices. The relevance of this compound to the toxicity of arsenic in humans is unknown and further exposure assessment and metabolic studies are difficult to conduct because of the unavailability of a well characterized standard. The synthesis of DMTA^V was accomplished by the reaction of dimethylarsinic acid (DMA^V) with hydrogen sulfide. The initial reaction product produced is DMTA^V but multiple products over the course of the reaction are also observed. Therefore, a chromatographic separation was developed to monitor the reaction progress via LC–ICP-MS. In this synthesis, conversion of DMA^V to DMTA^V was not taken to completion to avoid the production of side products. The product was isolated from the starting material by standard organic techniques. Single crystal diffraction demonstrated that solid DMTA^V is present in the form of the oxygen-bridged dimethylthioarsinic anhydride. Dissolution of the anhydride in water produces the acid form of DMTA^V and the aqueous phase DMTA^V provided a characteristic molecular ion of m/ z 155 by LC–ESI-MS. The synthesis and isolation of dimethylthioarsinic anhydride provides a stable crystalline standard suitable for identification, toxicological study and exposure assessment of dimethylthioarsinic acid.

Keywords: Inductively coupled plasma-mass spectrometry; Electrospray ionization-mass spectrometry; Dimethylarsinic acid; Dimethylarsinothioic acid; Hydrogen sulfide; Speciation

Dimethylthioarsinic anhydride: A standard for arsenic speciation by Michael Fricke; Matthias Zeller; William Cullen; Mark Witkowski; John Creed (pp. 78-83).

Keywords: Inductively coupled plasma-mass spectrometry; Electrospray ionization-mass spectrometry; Dimethylarsinic acid; Dimethylarsinothioic acid; Hydrogen sulfide; Speciation

Investigation of mercury-containing proteins by enriched stable isotopic tracer and size-exclusion chromatography hyphenated to inductively coupled plasma-isotope dilution mass spectrometry by Junwen Shi; Weiyue Feng; Meng Wang; Fang Zhang; Bai Li; Bing Wang; Motao Zhu; Zhifang Chai (pp. 84-91).

In order to investigate trace mercury-containing proteins in maternal rat and their offspring, a method of enriched stable isotopic tracer (¹⁹⁶Hg and¹⁹⁸Hg) combined with size-exclusion chromatography (SEC) coupled to inductively coupled plasma-isotope dilution mass spectrometry (ICP-IDMS) was developed. Prior to the analysis,¹⁹⁶Hg- and¹⁹⁸Hg-enriched methylmercury was administrated to the pregnant rats. Then the mercury-containing proteins in serum and brain cytosol of the dam and pup rats were separated by size-exclusion columns and the mercury was detected by ICP-MS. The ICP-MS spectrogram of the tracing samples showed significantly elevated¹⁹⁶Hg and¹⁹⁸Hg isotopic signals compared with the natural ones, indicating that the detection sensitivity could be increased by the tracer method. The contents of mercury in chromatographic fractions of the dam and pup rat brain cytosol were quantitatively estimated by post-column reverse ID-ICP-MS. The quantitative speciation differences of mercury in brain cytosol between the dam and pup rats were observed, indicating that such studies could be useful for toxicological estimation. Additionally, the isotopic ratio measurement of¹⁹⁸Hg/²⁰²Hg in the tracing samples could be used to identify the artifact mercury species caused in the analytical procedure. The study demonstrates that the tracer method combined with high-performance liquid chromatography (HPLC)-ICP-IDMS could provide reliably qualitative and quantitative information on mercury-containing proteins in organisms.

Keywords: Mercury-containing proteins; Stable isotopic tracer; Size-exclusion chromatography; Reverse isotope dilution ICP-MS

Speciation of inorganic selenium using capillary electrophoresis–inductively coupled plasma-atomic emission spectrometry with on-line hydride generation by Biyang Deng; Jinrong Feng; Jun Meng (pp. 92-97).

A novel and simple hydride generator has been developed. The hydride generator has good stability and high gas liquid separation efficiency. The generator serves as an interface of capillary electrophoresis (CE) and inductively coupled plasma atomic emission spectrometry (ICP-AES). This device eliminates the nebulization step and overcomes the common problem of suction flow resulting from the use of nebulization gas in ICP. Selenium compounds that were separated by CE were converted into the corresponding volatile hydrides, followed by ICP-AES measurement. The effects of the concentration of the hydride generating reagents (HCl and NaBH₄), the carrier gas flow rate, and heavy metal interference on Se emission intensity were discussed. The relative standard deviations (RSDs) of peak area, based on six determinations of 50ngmL⁻¹ standard of Se^IV and Se^VI, were 1.5% and 1.8%, respectively. The detection limits (3 σ) of peak area were 2.1ngmL⁻¹ and 2.3ngmL⁻¹ for Se^IV and Se^VI, respectively. Speciation analysis of inorganic Se^IV and Se^IV species using the HG-CE–ICP-AES system was demonstrated in tap and river water samples.

Keywords: Capillary electrophoresis; Hydride generation; Inductively coupled plasma-atomic emission spectrometry; Selenium; Speciation analysis

Determination of benzyltriethyl ammonium chloride from polymeric media by capillary electrophoresis with ultraviolet absorbance detection by Weisheng Lin; Haiying Shi; Trisha May; Honglan Shi; Yinfa Ma (pp. 98-102).

The importance of benzyltriethyl ammonium chloride (BTEAC) in industrial applications has stimulated the development of a number of methods for its determination. In this paper, a high performance capillary electrophoresis (CE) method, coupled with an extraction technique for determining BTEAC in organic matrices, was developed. BTEAC was extracted from organic samples with a 20mM sodium phosphate solution. Sonication was used to improve extraction efficiency. The repeatability and recovery of the technique have been studied and it was proven that the technique is satisfactory for quantitative determination of BTEAC in organic matrices. Separation was achieved within 6min in 20mM sodium phosphate buffer at pH 5.0. The recovery was above 92%. The detection limit for BTEAC is 5mgL⁻¹ with a signal-to-noise ratio of 3. The linear range of the technique is 5–100mgL⁻¹. This method is simple, fast, low-cost, and can be easily used for product quality control in industrial laboratories.

Keywords: Capillary electrophoresis; Benzyltriethyl ammonium chloride; Separation; Ultraviolet absorbance detection

Determination of 13 synthetic food colorants in water-soluble foods by reversed-phase high-performance liquid chromatography coupled with diode-array detector by Katerina S. Minioti; Christina F. Sakellariou; Nikolaos S. Thomaidis (pp. 103-110).

A reversed-phase high performance liquid chromatographic method for the successful separation and determination of 13 synthetic food colorants (Tartrazine E 102, Quinoline Yellow E 104, Sunset Yellow E 110, Carmoisine E 122, Amaranth E 123, Ponceau 4R E 124, Erythrosine E 127, Red 2G E 128, Allura Red AC E 129, Patent Blue V E 131, Indigo Carmine E 132, Brilliant Blue FCF E 133 and Green S E 142) was developed. A C18 stationary phase was used and the mobile phase contained an acetonitrile–methanol (20:80v/v) mixture and a 1% (m/v) ammonium acetate buffer solution at pH 7.5. Successful separation was obtained for all the compounds using an optimized gradient elution within 29min. The diode-array detector was used to monitor the colorants between 350 and 800nm. The method was thoroughly validated. Detection limits for all substances varied between 1.59 (E 142) and 22.1 (E 124)μgL⁻¹. The intra-day precision (as R.S.D._r) ranged from 0.37% (E 122 in fruit flavored drink at a concentration of 100mgL⁻¹) to 4.8% (E 142 in icing sugar at a level of 0.9mgkg⁻¹). The inter-day precision (as R.S.D._R) was between 0.86% for E 122 in fruit flavored drink at 100mgL⁻¹ and 10% for E142 in jam at a concentration of 9mgkg⁻¹. Satisfactory recoveries, ranging from 94% (E 142 in jam) to 102% (E 131 in sweets), were obtained. The method was applied to the determination of colorants in various water-soluble foods, such as fruit flavoured drinks, alcoholic drinks, jams, sugar confectionery and sweets, with simple pre-treatment (dilution or water extraction).

Keywords: Liquid chromatography; Diode-array detector; Synthetic dyes; Food analysis; Confectionary; Soft drinks

Solid-phase extraction-fluorimetric high performance liquid chromatographic determination of domoic acid in natural seawater mediated by an amorphous titania sorbent by Ivy O.M. Chan; Vic W.H. Tsang; K.K. Chu; S.K. Leung; Michael H.W. Lam; T.C. Lau; Paul K.S. Lam; Rudolf S.S. Wu (pp. 111-117).

The feasibility of using sol–gel amorphous titania (TiO₂) as a solid-phase sorbent for the pre-concentration of domoic acid (DA), a potent amnesic shellfish poisoning (ASP) toxin, directly from seawater was explored. The sol–gel titania material is able to adsorb DA from seawater, via the formation of ester-linkage between the carboxylic moieties of DA and the Ti–OH groups on the sorbent surface, at low pH and desorb it at high pH. The chemisorption process is not significantly interfered by the seawater matrix. The optimum pH values for the adsorption and desorption of DA were found to be pH 4 and 11, respectively. The optimal sorbent loading for the batch-type solid-phase extraction of DA was 0.67mg-TiO₂ng-DA⁻¹ and adsorption equilibrium was achieved in 2h at room temperature. The desorbed DA in 500μL of 0.1M alkaline borate buffer can be directly derviatized by 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) in aqueous media for fluorimetric HPLC quantification. Analyte recovery, repeatability and detection limit of this titania SPE-fluorimetric HPLC determination are 89%, 6.2% and 120pg-DAmL⁻¹ ( n=7, P<0.05), respectively, for a sample volume of 30mL. This titania SPE technique should also be applicable to the pre-concentration of other polar carboxylate- and phosphonate-containing biomolecules and pharmaceuticals in complex and interfering environmental sample matrices.

Keywords: Domoic acid; Amnesic shellfish poisoning; Algal toxin; Harmful algal blooms; Titania; Sol–gel; Solid-phase extraction

Determination of itopride in human plasma by liquid chromatography coupled to tandem mass spectrometric detection: Application to a bioequivalence study by Heon-Woo Lee; Ji-Hyung Seo; Seung-Ki Choi; Kyung-Tae Lee (pp. 118-123).

A simple method using a one-step liquid–liquid extraction (LLE) with butyl acetate followed by high-performance liquid chromatography (HPLC) with positive ion electrospray ionization tandem mass spectrometric (ESI-MS/MS) detection was developed for the determination of itopride in human plasma, using sulpiride as an internal standard (IS). Acquisition was performed in multiple reaction monitoring (MRM) mode, by monitoring the transitions: m/ z 359.5>166.1 for itopride and m/ z 342.3>111.6 for IS, respectively. Analytes were chromatographed on an YMC C₁₈ reverse-phase chromatographic column by isocratic elution with 1mM ammonium acetate buffer–methanol (20: 80, v/v; pH 4.0 adjusted with acetic acid). Results were linear ( r²=0.9999) over the studied range (0.5–1000ngmL⁻¹) with a total analysis time per run of 2min for LC-MS/MS. The developed method was validated and successfully applied to bioequivalence studies of itopride hydrochloride in healthy male volunteers.

Keywords: Itopride; Liquid–liquid extraction; Liquid chromatography/tandem mass spectrometry; Human plasma; Bioequivalence

Cylindrospermopsin determination using 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid (HEPES) as the internal standard by Sachiko Kikuchi; Takuya Kubo; Kunimitsu Kaya (pp. 124-127).

Cylindrospermopsin (CYN) was determined by liquid chromatography/electrospray ionization-mass spectrometry (LC/ESI-MS) using 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid (HEPES) as the internal standard. In the selected ion monitoring of LC/ESI-MS, m/ z 414 for CYN and 237 for HEPES were monitored using the negative mode; the retention times of CYN and HEPES were 12.41 and 14.21min, respectively. CYN was determined from peak area ratios of m/ z 414/237. By the treatment of an anion exchange cartridge using a buffer at pH 10.5, CYN was isolated and condensed. No interfering peak was observed. Linearity of this method was observed at the range of 0.10–31.12ng. Total coefficients of variation were 5.1 and 2.9% at 104 and 1038μgCYNL⁻¹. The quantitative limit at a signal-to-noise (S/N) ratio of 10 was 0.16ng.CYN concentration in natural waters is low. CYN in waters should be condensed for determination. This method including the treatment for isolation and condensation of CYN is useful for determination of CYN in environmental and/or drinking waters.

Keywords: Cyanobacterial toxin; Cylindrospermopsin; Internal standard; (2[4-(2-Hydroxyethyl)-1-piperazinyl]ethanesulfonic acid) (HEPES); Liquid chromatography/electrospray ionization-mass spectrometry (LC/ESI-MS); Selected ion monitoring (SIM)

Cylindrospermopsin determination using 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid (HEPES) as the internal standard by Sachiko Kikuchi; Takuya Kubo; Kunimitsu Kaya (pp. 124-127).

Temporal characterisation of river waters in urban and semi-urban areas using physico-chemical parameters and chemometric methods by M. Felipe-Sotelo; J.M. Andrade; A. Carlosena; R. Tauler (pp. 128-137).

Three sampling campaigns were carried out in rivers located at two hydrographic basins affected by urban and semi-urban areas around the Metropolitan area of A Coruña (ca. 500,000 inhabitants, NW-Spain) to study local and temporal variations of 21 physicochemical parameters (pH, conductivity, Cl⁻, SO₄²⁻, SiO₂, Ca²⁺, Mg²⁺, Na⁺, K⁺, hardness, NO₃⁻, NO₂⁻, NH₄⁺, COD, PO₄³⁻, Zn²⁺, Cu²⁺, Mn²⁺, Pb²⁺, alkalinity and acidity) in 23 sampling points. The temporal evolution of the water quality was assessed by matrix augmentation principal components analysis (MA-PCA) and parallel factor analysis (PARAFAC). Moreover, classical principal components analysis (PCA) (one per sampling campaign) was applied with exploratory and comparison purposes. The first factor of the different studies comprised variables associated to the mineral content and it differentiated the samples according to their hydrographic basins. The second factor was mainly associated to organic matter, from domestic wastes and decomposition of natural debris. The temporal evolution of the water quality was mostly related to seasonal increments of the physicochemical parameters defining the decomposition of the organic matter.The three models applied (PCA, MA-PCA and PARAFAC) led to similar conclusions, nonetheless, MA-PCA excelled, since the refolding of scores provided more straightforward and convenient overview of sample time and geographical variations than individual PCA and it is more flexible and adaptable to environmental studies than PARAFAC.

Keywords: River waters; Principal components analysis (PCA); Parallel factor analysis (PARAFAC); Matrix augmentation-PCA

Q-mode curve resolution of UV–vis spectra for structural transformation studies of anthocyanins in acidic solutions by Paulo Henrique Março; Ieda Spacino Scarminio (pp. 138-146).

Chemometric analysis of ultraviolet–visible (UV–vis) spectra for pH values 1.0, 3.3, 5.3, and 6.9 was used to investigate the kinetics and the structural transformations of anthocyanins in extracts of calyces of hibiscus flowers of the Hibiscus acetosella Welw. ex Finicius for the first time. Six different species were detected: the quinoidal base (A), the flavylium cation (AH⁺), the pseudobase or carbinol pseudobase (B), cis-chalcone (C_C), trans-chalcone (C_t), and ionized cis-chalcone (CC−). Four equilibrium constant values were calculated using relative concentrations, hydration, p K_h=2.60±0.01, tautomeric, K_T=0.14±0.01, acid–base, p K_a=4.24±0.04, and ionization of the cis-chalcone,pKCC=8.74±1.5×10−2. The calculated protonation rate of the tautomers isKH+=0.08±7.6×10−3. These constants are in excellent agreement with those measured previously in salt form. From a kinetic viewpoint, the situation encountered is interesting since the reported investigation is limited to visible light absorption in acid medium. These models have not been reported in the literature.

Keywords: Anthocyanins; Chemometric analysis; UV–vis spectrometry; Kinetic studies

Q-mode curve resolution of UV–vis spectra for structural transformation studies of anthocyanins in acidic solutions by Paulo Henrique Março; Ieda Spacino Scarminio (pp. 138-146).

Keywords: Anthocyanins; Chemometric analysis; UV–vis spectrometry; Kinetic studies

Study of the sensitization of tetradecyl benzyl dimethyl ammonium chloride for spectrophotometric determination of dopamine hydrochloride using sodium 1,2-naphthoquinone-4-sulfonate as the chemical derivative chromogenic reagent by Quanmin Li; Juan Li; Zhanjun Yang (pp. 147-152).

A new method has been established for the determination of dopamine hydrochloride (DPH) using sodium 1,2-naphthoquinone-4-sulfonate (NQS) and tetradecyl benzyl dimethyl ammonium chloride (Zeph). This method is based on the formation of a pink compound from the reaction of DPH, sodium 1,2-naphthoquinone-4-sulfonate and Zeph. The condensation reaction proceeds quantitatively in pH 9.40 buffer solution. The maximum absorption wavelength and the value of ɛ₄₉₁ were 491nm, and 7.51×10³lmol⁻¹cm⁻¹, respectively, when the stoichiometric ratio of the reaction was 1:1:1. Beer′s law was obeyed in the range of 0.16–40mgl⁻¹ of DPH. The data have been filled to a linear regression equation A=0.5781+0.0254 C (mgl⁻¹), with a correlation coefficient of 0.9993. The detection limit is 0.12mgl⁻¹, R.S.D. is 0.64% (40mgl⁻¹, n=11), and average recovery is over 99.7%. This paper further improves the determination of DPH compared to the previous methods. The kinetic property and reaction mechanism have also been discussed. This proposed method has been successfully applied to the determination of DPH in injection and biological samples with satisfactory results.

Keywords: Dopamine hydrochloride; Sodium 1,2-naphthoquinone-4-sulfonate; Spectrophotometry; Tetradecyl benzyl dimethyl ammonium chloride

Development of an immunosensor for the detection of testosterone in bovine urine by Gráinne Conneely; Margaret Aherne; Huihui Lu; George G. Guilbault (pp. 153-160).

In the presented work, a disposable immunosensor for the detection of testosterone, an endogenous steroid hormone, in bovine urine has been developed using screen-printed electrodes (SPEs). Due to concerns over the use of steroid hormones as growth promoters, the EU prohibits their use in food producing animals. Consequently, rigorous screening procedures have been implemented in all member states to detect the illegal administration of such compounds. Competitive immunoassays were developed, initially by enzyme linked immunosorbent assay (ELISA), and subsequently transferred to an electrochemical immunosensor format using disposable screen-printed carbon electrodes. Horseradish peroxidase (HRP) was the enzyme label of choice and chronoamperometric detection was carried out using a tetramethylbenzidine/hydrogen peroxide (TMB/H₂O₂) substrate system, at +100mV. The EC₅₀ values obtained for the assay in buffer and urine gave relatively comparable results, 710pgmL⁻¹ and 960pgmL⁻¹, respectively. The linear range obtained for the assay in buffer extended from 0.03ngmL⁻¹ to 40ngmL⁻¹; while that in urine ranged from 0.03ngmL⁻¹ to 1.6ngmL⁻¹. The corresponding limits of detection (LOD) in buffer and urine were 26pgmL⁻¹ and 1.8pgmL⁻¹. Cross reactivity profiles of the antibody have been examined, with notable cross reactivities with 19-nortestosterone (11.6%) and boldenone (9.86%). Precision studies for the sensor demonstrated adequate reproducibility (CV<13%, n=3) and repeatability (CV<9%, n=3). Recovery data obtained showed good agreement between spiking studies and known concentrations of analyte. Sensors showed stability for 4 days at +4°C. A sensitive, highly specific, inexpensive, disposable immunosensor, showing excellent overall performance for the detection of testosterone in bovine urine, has been developed.

Keywords: Testosterone; Immunosensor; Bovine urine; Screen-printed electrode

Development of an immunosensor for the detection of testosterone in bovine urine by Gráinne Conneely; Margaret Aherne; Huihui Lu; George G. Guilbault (pp. 153-160).

Keywords: Testosterone; Immunosensor; Bovine urine; Screen-printed electrode

Fluorescent biosensor using whole cells in an inorganic translucent matrix by Hanh Nguyen-Ngoc; Canh Tran-Minh (pp. 161-165).

An optical biosensor based on vegetal cells entrapped in an inorganic translucent matrix and fluorescence detection has been developed. The biosensor uses Chlorella vulgaris immobilized in a translucent support produced from sol–gel technology. The translucence of the structure enables the algal active layer to be placed directly in contact with the optical fibers for fluorescence detection. This configuration has many advantages over the use of an opaque support because no space between the optical fibers and the active layer is required to collect fluorescence. This reagentless biosensor allows determination of diuron as an anti-PSII herbicide and its long term activity is assessed.

Keywords: Fluorescent biosensor; Cell immobilization; Sol–gel; Translucent matrix; Chlorella vulgaris; Herbicides detection

Fluorescent biosensor using whole cells in an inorganic translucent matrix by Hanh Nguyen-Ngoc; Canh Tran-Minh (pp. 161-165).

Keywords: Fluorescent biosensor; Cell immobilization; Sol–gel; Translucent matrix; Chlorella vulgaris; Herbicides detection

Oxygen-sensing film coated photodetectors for portable instrumentation by L.F. Capitán-Vallvey; L.J. Asensio; J. López-González; M.D. Fernández-Ramos; A.J. Palma (pp. 166-173).

A sensor configuration for oxygen determination based on luminescence quenching is presented in which the measured parameter is closely related to the luminescence lifetime. The sensing film is based on the dye platinum octaethylporphyrin complex immobilised in a polystyrene membrane and stabilised with the heterocyclic amine DABCO. In this report, we study the feasibility of using photodiodes as elements to be coated by this oxygen sensing film with the aim of obtaining a sensing device whose small size makes it possible to embed it into a portable measurement system. In addition to the concomitant sensor miniaturisation, several advantages have been demonstrated such as fast response, low energy consumption, the lack of any need for optical filter elements and less tendency to photobleaching than with previous configurations. A complete study of the coated photodetector preparation was carried out in order to optimise the specifications of the portable instrument where the photodetector is included, such as: repeatability, transient response and selectivity. We propose a preparation procedure for coating photodetectors with this film that has demonstrated the capacity to produce repetitive and reliable sensing devices.

Keywords: Optical chemical sensor; Oxygen determination; Coated photodetectors; Luminescence quenching; Portable instrument; Integrated analytical system

Oxygen-sensing film coated photodetectors for portable instrumentation by L.F. Capitán-Vallvey; L.J. Asensio; J. López-González; M.D. Fernández-Ramos; A.J. Palma (pp. 166-173).

Keywords: Optical chemical sensor; Oxygen determination; Coated photodetectors; Luminescence quenching; Portable instrument; Integrated analytical system

A new generation of cyanide ion-selective membranes for flow injection application by Andriana R. Surleva; Valentina D. Nikolova; Milka T. Neshkova (pp. 174-181).

Using induced cathodic electrodeposition a number of silver chalcogenide thin layer membranes of non-trivial composition have been synthesized and their performance as ion-selective flow-injection potentiometric detectors (FIPDs) for free cyanide has been critically estimated in the context of the stringent requirements for toxic cyanide environmental monitoring. AgSCN/Ag₂S, Ag₂S, Ag2+_δSe, Ag2+_δSe1−_xTe_x (0< δ<0.25 and x≈0.13), Ag₂Se and Ag₂Se1−_xTe_x electroplated membranes were selected for the present performance-based comparative study in order to obtain a feedback information about the effect of membrane composition. Both silver selenide and Te-doped silver selenide membranes, irrespective of their stoichiometry with respect to silver, exhibit the lowest detection limit for CN⁻ (52ppb) with linear double-Nernstian response down to 130ppb. The type of chalcogene anion in the membrane composition proves to exert dominant effect on the general performance characteristics of the newly developed FIPDs. The silver stoichiometry (intrinsic defects factor) and the inclusion of Te-dopant (extrinsic defects factor) have more pronounced effect on the profile of the output signal and exert moderate control on the detectors selectivity and baseline stability. This new generation of CN⁻—ion-selective membranes for FIPDs exhibits high selectivity against the common interferents present in cyanide effluents such as SCN⁻, S₂O₃²⁻, Cl⁻ and do not get poisoned in the presence of S²⁻. Moreover, their long-term stability and signal reproducibility, which make redundant the regular day-to-day calibration, coupled with the cost-effective technology for membranes preparation and easy re-generation make them attractive candidates for incorporation into automated in-field devices for in situ cyanide toxic species monitoring.

Keywords: AgSCN/Ag; ₂; S; Ag; ₂; S; Ag; 2+; _δ; Se; Ag; 2+; _δ; Se; 1−; _x; Te; _x; (0; <; δ; <; 0.25 and; x; ≈; 0.13); Ag; ₂; Se; Ag; ₂; Se; 1−; _x; Te; _x; —electroplated thin membranes; Flow injection; Cyanide potentiometric detectors; Environmental monitoring

A new generation of cyanide ion-selective membranes for flow injection application by Andriana R. Surleva; Valentina D. Nikolova; Milka T. Neshkova (pp. 174-181).

Simultaneous detection of ascorbate and uric acid using a selectively catalytic surface by Hossam M. Nassef; Abd-Elgawad Radi; Ciara O'Sullivan (pp. 182-189).

The direct and selective detection of ascorbate at conventional carbon or metal electrodes is difficult due to its large overpotential and fouling by oxidation products. Electrode modification by electrochemical reduction of diazonium salts of different aryl derivatives is useful for catalytic, analytical and biotechnological applications. A monolayer of o-aminophenol ( o-AP) was grafted on a glassy carbon electrode (GCE) via the electrochemical reduction of its in situ prepared diazonium salts in aqueous solution. The o-aminophenol confined surface was characterized by cyclic voltammetry. The grafted film demonstrated an excellent electrocatalytic activity towards the oxidation of ascorbate in phosphate buffer of pH 7.0 shifting the overpotential from +462 to +263mV versus Ag/AgCl. Cyclic voltammetry and d.c. amperometric measurements were carried out for the quantitative determination of ascorbate and uric acid. The catalytic oxidation peak current was linearly dependent on the ascorbate concentration and a linear calibration curve was obtained using d.c. amperometry in the range of 2–20μM of ascorbate with a correlation coefficient 0.9998, and limit of detection 0.3μM. The effect of H₂O₂ on the electrocatalytic oxidation of ascorbate at o-aminophenol modified GC electrode has been studied, the half-life time and rate constant was estimated as 270s, and 2.57×10⁻³s⁻¹, respectively. The catalytically selective electrode was applied to the simultaneous detection of ascorbate and uric acid, and used for their determination in real urine samples. This o-AP/GCE showed high stability with time, and was used as a simple and precise amperometric sensor for the selective determination of ascorbate.

Keywords: Ascorbate; Uric acid; Diazonium salt; Modified electrode; Electrocatalysis

Simultaneous detection of ascorbate and uric acid using a selectively catalytic surface by Hossam M. Nassef; Abd-Elgawad Radi; Ciara O'Sullivan (pp. 182-189).

Keywords: Ascorbate; Uric acid; Diazonium salt; Modified electrode; Electrocatalysis

Selectivity enhancement of anion-responsive electrodes by pulsed chronopotentiometry by Kebede L. Gemene; Alexey Shvarev; Eric Bakker (pp. 190-196).

A large and robust selectivity improvement of ion-selective electrodes is presented for the measurement of abundant ions. An improvement in selectivity by more than two orders of magnitude has been attained for the hydrophilic chloride ions measured in a dilute background of the lipophilic ions perchlorate and salicylate in a pulsed chronopotentiometric measurement mode. This is attributed to a robust kinetic discrimination of the dilute lipophilic ions in this measuring mode, which is not possible to achieve in classical potentiometry. Maximum tolerable concentrations of the interfering ions are found to be on the order of 30μM before causing substantial changes in potential. As an example of practical relevance, the robust detection of chloride in 72μM salicylate (reflecting 1:10 diluted blood) with a detection limit of 0.5mM chloride is demonstrated. Corresponding potentiometric sensors did not give a useful chloride response under these conditions.

Keywords: Ion-selective electrodes; Selectivity enhancement; Clinical analysis; Anion detection; Solvent polymeric membrane

Selectivity enhancement of anion-responsive electrodes by pulsed chronopotentiometry by Kebede L. Gemene; Alexey Shvarev; Eric Bakker (pp. 190-196).

Keywords: Ion-selective electrodes; Selectivity enhancement; Clinical analysis; Anion detection; Solvent polymeric membrane

Determination of equilibrium humidities using temperature and humidity controlled X-ray diffraction (RH-XRD) by Kirsten Linnow; Michael Steiger (pp. 197-201).

Confined growth of crystals in porous building materials is generally considered to be a major cause of damage. We report on the use of X-ray diffraction under controlled conditions of temperature and relative humidity (RH-XRD) for the investigation of potentially deleterious phase transition reactions. An improved procedure based on rate measurements is used for the accurate and reproducible determination of equilibrium humidities of deliquescence and hydration reactions. The deliquescence humidities of NaCl (75.4±0.5% RH) and Ca(NO₃)₂·4H₂O (50.8±0.7% RH) at 25°C determined with this improved RH-XRD technique are in excellent agreement with available literature data. Measurement of the hydration of anhydrous Ca(NO₃)₂ to form Ca(NO₃)₂·2H₂O revealed an equilibrium humidity of 10.2±0.3%, which is also in reasonable agreement with available data. In conclusion, dynamic X-ray diffraction measurements are an appropriate method for the accurate and precise determination of equilibrium humidities with a number of interesting future applications.

Keywords: X-ray diffraction; Humidity control; Kinetics; Phase transformation; Deliquescence; Hydration

Determination of equilibrium humidities using temperature and humidity controlled X-ray diffraction (RH-XRD) by Kirsten Linnow; Michael Steiger (pp. 197-201).

Keywords: X-ray diffraction; Humidity control; Kinetics; Phase transformation; Deliquescence; Hydration

Influence of water filtration on the determination of a wide range of dissolved contaminants at parts-per-trillion levels by Anna Gómez-Gutiérrez; Eric Jover; Josep M. Bayona; Joan Albaigés (pp. 202-209).

The adsorption of dissolved organic contaminants on glass fibre filters throughout water dissolved/particulate phase decoupling studies was examined. A total of 49 different compounds were considered at low concentration levels (ngL⁻¹), including PAHs, PCBs, organochlorine and organophosphorus pesticides, triazines, thiocarbamates, pyrethroids, phosphate esters and caffeine. Their adsorption on the filters was positively correlated with their logKow and solubilities, indicating that filter adsorption increased with hydrophobicity. The influence of water properties (i.e. salinity and dissolved organic carbon (DOC) content) was also studied by means of a star experimental design ( n=11). Salinity was the main factor in increasing the adsorption, due to the salting out effect. The influence of DOC suggested that part of the contaminant losses during water filtration may have been caused by the retention on the organic matter adsorbed on the filter surface. Nevertheless, a decrease in filter retention was observed for water with the highest DOC contents, which was probably due to an enhancement of the contaminant solubility in these conditions. Although several factors may control the adsorption process in naturally occurring waters, the extent of the retention of dissolved target analytes on the glass fibre filters should not be underestimated in the analysis of hydrophobic contaminants in marine and estuarine waters at very low concentrations (ppt level).

Keywords: Filter adsorption; Dissolved/particulate partitioning; Organic contaminants; Dissolved organic carbon; Water salinity

Enhancement of the detection sensitivity for volatile organic compounds by using an annular type photoionization detector and a pre-concentration system by Kyuseok Song; Bowha Ahn; Euochang Jung; Yong-Ill Lee; Sungsuk Ko (pp. 210-215).

Photoionization detector (PID) was developed for a sensitive on-site detection of trace amounts of volatile organic compounds (VOCs) based on an annular type ion collection electrode assembly. An ion collector with an annular geometry could detect more stable ion signals in the PID system when compared to the other types of ion collectors when an UV lamp of 10.6eV was used as an ionization source. In order to enhance the detection sensitivity, a pre-concentration system, which was developed by adopting a ceramic heater packed with rod shaped molecular sieves, was adopted for a detection of VOCs. The adopted ceramic heaters had a resistance of 10–20Ohm, and the temperature of the heater was optimized by controlling the heating time of the resistor. The enhancement of the detection sensitivity was found to be 8–10 times with the PID system when compared to the signals measured without a pre-concentrator. The overall detection sensitivity of the developed PID system was estimated as 10ppb or better.

Keywords: Volatile organic compounds; Photoionization detection; Pre-concentration

Erratum to “Utilizing a sequential injection system furnished with an extraction microcolumn as a novel approach for executing sequential extractions of metal species in solid samples” [Anal. Chim. Acta 526 (2004) 177–184] by Roongrat Chomchoei; Elo Harald Hansen; Juwadee Shiowatana (pp. 216-216).

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Analytica Chimica Acta (v.583, #1)