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Anal Bioanal Chem

This article investigates the controls on sediment phosphorus (P) speciation dynamics as a function of its fractionation into chemically defined operational pools along a river continuum. A total of 27 variables were analyzed in bed sediment samples collected for one year from six sampling points, along a 75 km river continuum (Louros River, NW Greece). Multivariate explanatory analysis of the complex experimental data matrix was performed in order to unravel the spatial pattern of P speciation. Non-parametric examinations were also applied in order to elucidate the temporal variations encountered in the speciation of P. The results suggest that inorganic P species control P bioavailability in space and time. Organic P was found to be very reactive among the various fractions thus changing its bioavailability but exhibited no temporal variation. The utility of the proposed approach in the differentiation of natural and anthropogenic P inputs and their classification to point and non-point sources is demonstrated presenting a significant improvement compared to mere fractionation analysis. (c) 2006 Elsevier Ltd. All rights reserved. Water Res

A combination of non-parametric explanatory procedures and pattern recognition techniques is introduced in this study as an alternative tool to the assessment of sedimentary P fractionation. The complex raw data matrix was treated with a series of parametric and non-parametric techniques such as correlation analysis, cluster analysis, factor analysis/principle components analysis, discriminant analysis, multidimensional scaling, Kruskal-Wallis analysis of variance and non-parametric median test. Each of these procedures has been directed towards the identification of specific mechanisms that control P biogeochemistry in the river sediment. Non-parametric tests were proven as a very powerful tool in interpreting temporal variations of the data in a short-term basis as opposed to previous procedures predicting seasonal or annual changes. On the other hand, parametric techniques were not always able to delineate a reduced number of indicator variables responsible for the large variations in sediment quality, necessitating the application of various techniques in order to interpret the intricate mechanisms occurring in the sediment phase. The examined procedures provide the basis for identifying the patterns of sedimentary P associated with seasonal and spatial patterns, pollution sources as well as differentiate between natural and non-natural inputs, presenting an alternative approach for environmental quality assessments. Desalination

This work reports on the fabrication of a mini column packed with controlled pore glass and glass wool, and its application for the on-line preconcentration of lead with the aid of an anionic surfactant ( sodium dodecyl sulphate, SDS) and AAS detection. Lead reacts with SDS in a highionic-strength environment, and the product is retained and preconcentrated on a high-surface area substrate like glass wool. The intervention of controlled pore glass increases the active surface of glasswool and prevents its accumulation into a sticky mass after wetting. Washing the mini column with a methanolic solution of HNO3, causes the retained micellar face to be eluted, and consequently the lead content can be determined with AAS. A preconcentration factor of 50 along with a signal enhancement due to the combined presence of SDS and methanol yields a detection limit of 1.5 mu g L-1. The correlation coefficient of the calibration curve is 0.999, and the linear range 5-500 mu g L-1. The method was used for the determination of lead in water and wastewater with good results. International Journal of Environmental Analytical Chemistry

The monitoring of dissolved metal species in natural waters is pursued through the development, optimization and verification of a multi-elemental extraction procedure based on the cloud point phenomenon. More specifically, six metal species were extracted from water samples as their pyrrolidinedithiocarbamate complexes and subsequently isolated from the aqueous matrix in the micelles of a non-ionic surfactant upon increase of the solution temperature. The optimum experimental conditions that ensure the efficiency of the procedure have been investigated and are presented in detail. As an analytical demonstration, the method was applied to the monitoring survey of two natural ecosystems in Northwestern Greece in an annual monitoring study. The measured concentrations of dissolved metal species were deployed to estimate the pollution status of the ecosystems and unravel the mechanisms that contribute to the metal load. (c) 2005 Elsevier B.V. All rights reserved. Analytica Chimica Acta

We present contemporary developments in the field of surfactants and micellar systems together with their applications in analysis, with the aim of highlighting some of the most important aspects of this area of research. We pay particular attention to speciation through cloud-point extraction (CPE), as well as to the differentiation of metallic species, oxidation states and complexes prior to their determination. We also present a theoretical background and a guide for experimentally optimizing CPE. We conclude by discussing some problems arising from the use of surfactant systems, while proposing future trends and potential new areas for their application. (c) 2005 Elsevier Ltd. All rights reserved. Trac-Trends in Analytical Chemistry

The first amperometric biosensing method for the determination of L-fucose is described. L-Fucose is the objective of much current research, as it is considered as a potential marker for various pathologic disorders. Recombinant L-fucose dehydrogenase, having as cofactor beta-nicotinamide adenine dinucleotide phosphate (NAD(+)P), was cross-linked in a water-soluble photosensitive polymer matrix, that is, polyvinyl alcohol (PVA) modified with styrylpyridinium (SbQ), in the presence of BSA and glutaraldehyde. The resulting membrane was sandwiched between two polycarbonate membranes and was mounted in an amperometric cell. The oxidation of the enzymatically produced NADPH was monitored at a platinum anode at +0.25 V versus a silver pseudoreference electrode in the presence of ferricyanide. The system was fully optimized with respect to various analytical parameters. Regarding to the mechanical properties of the membrane and the storage stability of the immobilized enzyme, various parameters were also optimized. Several methods for the pretreatment of urine samples were investigated. Treatment of the samples with PbO2 found to eliminate the interference effect of various electroactive species exist in urine; optimum incubation time was determined since at prolonged incubation times L-fucose is also affected. Calibration curves for the direct and the mediated monitoring of NADPH were liner over the concentration ranges 0.04-1.0 mM (r(2) = 0.9995) and 0.03-3.0 mM (r(2) = 0.9997) fucose, respectively. The detection limits (S/N 3) were 2 and 1.5 muM fucose, respectively. The R.S.D. of the mediated biosensor is better than 1.5% (n = 10, 0.5 mM fucose). The proposed biosensor correlates well with a reference enzymatic method and exhibits very good working and storage stability. (C) 2004 Elsevier B.V. All rights reserved. Biosens Bioelectron

A comparative study between cloud point extraction (CPE) and low-temperature directed crystallization (LTDC) is presented. Trace elements (Cd, Pb, Cr, Cu, Zn, Ni and Fe) were preconcentrated by both methods from model and natural water samples and the results were evaluated with respect to extraction efficiency, accuracy, precision, sample throughput and interferences. Flame atomic absorption spectrometry (FAAS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) were used for the final measurements. The results indicate that these extraction and preconcentration procedures ensure the required accuracy and precision for the reliable identification and quantification of trace elements in natural waters. Drawbacks of each method identified can further assist the analyst towards a better application of each method depending on the target species, the detector employed and the application intended (routine analysis, trace analysis, speciation analysis, etc.). (C) 2003 Elsevier Science B.V. All rights reserved. Analytica Chimica Acta

The phase separation of lamellar vesicles of anionic surfactants in aqueous solutions and its application as a novel liquid coacervate extraction procedure was examined. Solutions of lauric acid sodium salt separate into two phases in the presence of alkaline earth metals and a water miscible cosurfactant. It is proven that the surfactant phase is built of a perplexed network of multilamellar vesicles consisting of densely packed bilayers. Several factors affecting the formation of this new phase as well as its analytical utility in the preconcentration of metallic ions were assessed on the basis of better exploitation of this new nonspecific extraction technique. In essence, although the procedure to arrive at the optimum conditions seems laborious, the delivered method is straightforward, alleviating the requirement for prereaction with a complexing agent and highly reproducible under the optimum experimental conditions. As an analytical demonstration, the method was successfully applied to the determination of Cd2+ and Zn2+ in natural waters. Recoveries were higher than 95%, and detection limits as low as 3 mug L-1 were accomplished by preconcentrating only 10 mL of sample volume in the presence of 0.45% (w/v) anionic surfactant. Anal Chem

Squaric acid (1,2-dihydroxy-3,4-diketo-cyclobutene) is used in a specific reaction with Fe(III) for the spectrophotometric determination of Fe(III) and total iron content. The optimization of the experimental parameters leads to the establishment of a simple, fast and accurate analytical method. The analytical procedure includes mixing ammonium squarate (40 mM), prepared in a phthalate buffer solution of pH 2.7, with the sample and measuring the absorbance at 515 nm. The molar absorptivity of the colored product is 3.95x10(3) L.mol(-1).cm(-1), at 515 nm. Calibration graphs for Fe(III) are rectilinear for 0.5-20 mgL(-1), with a detection limit of 0.3 mgL(-1) and r.s.d. not exceeding 2.5%, for five replicates of a 3.0 mgL(-1) standard solution. The method has been successfully applied to the determination of iron (III) and the total iron content after quantitative oxidation of iron (II). The results for several analyzed samples when compared with those acquired by using the FAAS technique, were found to be in satisfactory agreement. Microchimica Acta

Journal of Chemical Education

The traditional method for phenol analysis based on the oxidizing coupling of 4-aminoantipyrine (4-APP) with phenol in alkaline solution is re-evaluated in this study in combination with micellar assisted preconcentration (cloud point extraction). The method employs the conventional reaction pathway while extraction is facilitated by surfactant based precipitation, during which the nonpolar derivative of 4-AAP-phenol is entrapped in the micelles and concentrated into a surfactant-rich phase. The latter is the re-solubilized and the complex is quantified spectrophotometrically in the presence of a surfactant. Compared to the traditional method the modification proposed offers certain analytical advantages like massive analysis of many samples, lower detection limits and shorter time of analysis. The method was applied in various samples of different origin with satisfactory results. International Journal of Environmental Analytical Chemistry

The on-line incorporation of cloud point extraction (CPE) to flow injection analysis (FIA) is modified to extract and preconcentrate metal species rapidly, avoiding the formation of hydrophobic complexes, using a mixed micellar medium. Coupling the procedure with chemiluminescence (CL) detection based on the catalytic activity of metal species on the luminol-hydrogen peroxide reaction and enhancing the signal with the presence of a micellar carrier containing bromide ions produces a powerful tool for the preconcentration and determination of metal species at ng l(-1) levels. As an analytical demonstration ultratrace concentrations of chromium were conveniently detected and quantified in samples with a complex matrix such as seawater and wastewater. The figures of merit for the determination of chromium were: 0.9-1.6% R.S.D. (n = 5) with detection and quantification limits 0.5 and 2.0 ng l(-1), respectively. The calibration graph was rectilinear from 2 to 200 ng l(-1) (r = 0.9996, n = 6). Several other metal ions were determined in ideal situations, with analogous results. (C) 2002 Elsevier Science B.V. All rights reserved. Analytica Chimica Acta

The first amperometric flow analyzer, based on the biosensor concept, capable of determining total glucosinolates in real samples, is described. Myrosinase was immobilized on aminopropyl-modified controlled pore glass, which was then used for the construction of a packed-bed reactor. Myrosinase catalyzes the hydrolysis of glucosinolates (sinigrin) to glucose (among the other products), which is then oxidized by the action of glucose oxidase to produce hydrogen peroxide. The glucose enzyme electrode is based on a multimembrane architecture and was mounted on an amperometric flow cell (hydrogen peroxide detection at a platinum anode poised at +0.65 V vs Ag/AgCl/3M KCl). Different membrane types and different activation procedures were tested. The system was optimized to various working parameters, either as a glucose electrode or as a glucosinolate analyzer. The interference effect of various compounds was also investigated. Application of the method to real samples was carried out using glucose/glucose, hydrolyzed sinigrin and glucose/sinigrin solution as calibrators of the glucose electrode and the glucosinolate analyzer. Deviations due to the enantioselectivity of glucose oxidase to the beta-glucose anomer were observed, and a data elaboration protocol is proposed. The possibility of the simultaneous determination of glucose and glucosinolates is also demonstrated. Anal Chem

A new approach towards the spectrophotometric determination of ortho-phosphates is described. The method is based on the reaction of phosphate with the by-products of the oxidation reaction between diphenylamine and molybdenum (VI) in a formic acid solution environment. The final product absorbs at 340 nm allowing for the determination of ortho-phosphates at concentrations as low as 0.44 mg L-1 by using a very small sample volume. The calibration curve is linear in the range of 0.5-3 mg L-1 yielding recoveries higher than 96% in various sample matrices. Under the optimum experimental conditions side reactions with other ions that usually have high affinity for molybdenum ions are absent or minimum allowing for the interference free determination of PO43-. The only interference rises from the partial decomposition of organic or acid-hydrolysable phosphorus, which is codetermined with ortho-phosphates as a result of the extreme acidic conditions. However, their effects are minor compared to the interferences usually observed with the traditional methods. International Journal of Environmental Analytical Chemistry

In an effort to monitor orthophosphate in natural waters and wastewater in the Ipirous region (Greece), an analytical methodology was established owing to the need for interference-free determination at the low mg/l levels. The method applied for the determination of orthophosphate is based on its reaction with molybdate towards a yellow heteropoly acid complex, Which is electrically balanced with a cationic surfactant (cetylatrimethylammonium bromide) towards a complex non-polar derivative. This derivative is conveniently solubilized in the micelles of a non-ionic surfactant, under mild conditions and measured spectrophotometrically at 370 nm after its uptake with a sulfuric acid-methanol solution. By simply preconcentrating 10 ml of sample volume a detection limit of 2.6 muM was obtained. Due to the required dilution step and signal enhancement caused by the presence of surfactant, interference from the presence of anionic species (mostly silicate and arsenate) was minor and could be conveniently alleviated by the use of tartaric acid and Na2SO3, respectively. The method was successfully applied to real samples obtained for the natural sites subject., to the monitoring survey ranging in their matrix complexity from clean river water to wastewater. (C) 2002 Elsevier Science B.V. All rights reserved. Science of the Total Environment

This article describes an analytical method for the determination of magnesium taking advantage of the cloud point phenomenon employing a suitable chelating agent (chloranilate) for Mg analysis. The method encompasses pre-concentration of the metal chelate followed by flame atomic absorption spectrometry (FAAS) analysis. The chelating agent chosen for this task is a newly synthesised salt of chloranilic acid, trizma-chloranilate, which reacts with Mg but at the same time has a very low affinity for other metallic cations like silicon, aluminium and sodium, which interfere with the determination of Mg in FAAS. The condensed surfactant phase with the metal chelate(s) is introduced into the flame of an atomic absorption spectrometer after its treatment with an acidified methanolic solution. In this way, complex and time-consuming steps for sample treatment are avoided while increased sensitivity is achieved by the presence of both methanol and surfactant in the aspirated sample. The analytical curve was rectilinear in the range of 5-220 mug l(-1) and the limit of detection was as low as 0.75 mug l(-1) with a standard deviation of 5.2%. The method was applied for the determination of Mg in natural and mineral waters with satisfactory results and recoveries in the range of 97-102%. (C) 2002 Elsevier Science B.V. All rights reserved. Talanta

A highly selective spectrophotometric method for the determination of trace cobalt based upon the reaction of cobalt(III) with 1-(2-pyridylazo)-2-naphthol (PAN) in the presence of peroxodisulfate is described. Following an experimental design procedure based on a central composite design (CCD) method and a specifically orientated univariate optimization, it was found that an alkaline media of pH = 11 and controlled peroxodisulfate concentration are crucial factors for enhancing the formation and aqueous solubility of the Co(III)-PAN chelate. Immobilization of PAN into a cellulose acetate membrane was also investigated leading to the construction of a reagentless fiber-optic sensor. According to the proposed reaction mechanism dissolved Co(II) is easily oxidized to Co(III) by peroxodisulfate and then readily complexed with PAN, either in solution or on the membrane surface giving a unique absorbance peak at 645-650 nm. Linear calibration graphs over the concentration range 0.02-0.5 mg l(-1) with a 3sigma limit of detection of 0.01 and 0.1-2 mg l(-1) with a limit of detection of 0.07 mg l(-1) were obtained by applying the photometric method and the fiber-optic sensor, respectively. Excellent agreement with the reference atomic absorption spectrometric method was achieved when the proposed methodology was applied for the determination of cobalt in various samples of industrial, environmental and biological importance. (C) 2002 Elsevier Science B.V. All rights reserved. Analytica Chimica Acta

A method has been developed for the simultaneous determination of traces of Fe(III) and Fe(II) in water by on-line coupling of spectrophotometry with flame atomic absorption spectrometry (FAAS). The method involves cloud-point extraction (CPE) of both species with ammonium pyrrolidinecarbodithioate (APDC) under standard conditions, which facilitates the in situ complexation and extraction of both species. Differentiation of the oxidation states of iron is achieved by using mathematical equations to overcome the interference of Fe(Ill) in the spectrophotometric determination of Fe(Il) when they are both present in the same solution. In this manner the time-consuming and labor-intensive steps of preoxidation of Fe(II) or reduction of Fe(III) are eliminated. By preconcentrating a 10-mL sample solution detection limits as low as 7 mug L-1, were obtained after a single-step extraction procedure. The relative standard deviation (n=4, 30 mug L-1) was 2.6% and 1.8% for spectrophotometry and FAAS, respectively. Recoveries in the range of 96-105% were obtained by analysis of spiked real samples. The method was further verified by analyzing a certified reference material (IMEP-9); for this the recovery was 98.5%. Anal Bioanal Chem

The first enzyme-based biosensors capable of determining glycolic acid in various complex matrixes, such as cosmetics, instant coffee, and urine, are presented in this paper. Two separate designs, both based on a three-membrane configuration consisting of an inner cellulose acetate membrane (CA) and an outer polycarbonate membrane (PC), which sandwich a membrane bearing the biomolecule(s), are proposed. Glycolate oxidase was immobilized onto a modified polyethersulfonate membrane by means of chemical bonding, and glycolate oxidase/catalase enzyme mixture was immobilized into a mixed-ester cellulose acetate membrane through physical adsorption. The membrane assemblies were mounted on an amperometric flow cell (hydrogen peroxide detection at a platinum anode poised at +0.65 V vs Ag/AgCl/3 KCl) or on an oxygen electrode, respectively. Both configurations were optimized with respect to various working parameters. The proposed biosensors are interference-free to common electroactive species and were successfully applied for the determination of glycolic acid in various samples, showing an excellent agreement with a reference photometric method. The validity of the proposed method in samples, in which the reference method was not applicable, was tested with recovery studies. Values of 102 +/- % were obtained. Inherent interference of oxalic acid was manipulated by using a primary amine-containing buffer and the enzyme catalase. Both systems were designed in order to be compatible with the current technology of the most widely used commercial analyzers. Anal Chem

An enzymatic method for the individual or simultaneous determination of pyruvic acid and acetaldehyde is described. Alcohol dehydrogenase (ADH) was immobilized onto aminopropyl-modified controlled pore glass, which was then used for the construction of packed-bed (PB) reactors. ADH catalyses the reduction of acetaldehyde to ethanol, in the presence of the coenzyme NADH, which is oxidized to NAD(+). Photometric measurements in a fully automated flow injection (FI) manifold are used to monitor the decrease of NADH absorbance at 340 run. The possibility of pyruvate measurements, by combining the above mentioned system with soluble pyruvate decarboxylase (PyDC) is also demonstrated. PyDC catalyses the decarboxylation of pyruvate to acetaldehyde. Analytical parameters such as the buffering system, working pH, flow rate, sample size, and NADH concentration were studied. The interference of various compounds present in real samples was also investigated. Linear calibration graphs over the ranges 0.08-1.25 and 0.04-0.4 mM acetaldehyde were constructed in the presence of 50 mM succinate pH 7.5 and 50 mM phosphate pH 7.0 buffering systems, respectively. A linear calibration graph over the range 0.08-1.25 mM pyruvate was also constructed in the presence of 50 mM succinate pH 7.5 buffer solution. The reactors remain active for more than 6 months under specified storage conditions. The maximal sample throughput is 30 h(-1) and the R.S.D. of the method is 0.9% for 0.2 mM acetaldehyde (n = 6). The suitability of the proposed method for real samples was tested by recovery studies. (C) 2002 Elsevier Science B.V. All rights reserved. Analytica Chimica Acta

A simple spectrophotometric method for the determination of copper is described herewith, based on the formation of colored species of Cu (II) with 5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione (Bismuthiol II) in the presence of a neutral surfactant, Triton X-114. The yellow colored complex of Cu (II)Bismuthiol-II-Triton X-114 shows maximum absorbance at 395 nm in water. The detection limit of the method is 0.03 mg/1 while the Beer's law is obeyed up to 1.2 mg/1 of the analyte in an aqueous medium. The validity of the method has been examined for the determination of copper in wines, food supplements and raisins. The results obtained were in good agreement with those obtained using flame atomic absorption spectrometry (FAAS). The method thus constitutes a handy alternative for the determination of copper (II) in nutritional samples. Microchimica Acta

A methodology utilizing the cloud point phenomenon for the determination of free and tannin-bound iron in wines is presented. The method employs precipitation of the tannins and other phenolic and insoluble compounds in the micelles of a non-ionic surfactant mixture (TX-100 and TX-45) upon increase of the solution temperature, which are subsequently separated from the initial solution by centrifugation. The surfactant-rich-phase containing the tannins and the insoluble iron fraction is directly aspirated into the nebulizer of a flame atomic absorption spectrometer after its uptake with a methanolic solution of HNO3. The supernatant is submitted to the same cloud point extraction procedure for the determination of free iron species in the presence of a chelating agent, ammonium pyrrolidine dithiocarbamate (APDC), in order to form water-insoluble complexes with free iron. The complexes are extracted in the micelles and directly analyzed after they are diluted in a methanolic solution as described above. The total content of iron was also determined by conventional methods for comparison, yielding satisfactory results. The calibration graph was rectilinear up to 0.35 mg 1(-1) Fe, with detection limits of 0.02 mg 1(-1) with a relative standard deviation of 2.4%. The method was successfully applied to red and white wines. (C) 2002 Elsevier Science B.V. All rights reserved. Analytica Chimica Acta

This review introduces the principles of amperometric detection e.g. oxygen electrodes. hydrogen peroxide electrodes, NADH detection, mediators-aid detection, conductive organic salts and wiring electrodes. A short categorization and description of the materials commonly used for the construction of electrodes, e.g., platinum, glassy carbon, different types of graphite. screen-printed electrodes, rigid carbon-polymer biocomposites, zeolites, clays, and polymeric membranes is given. Approaches to construction of biosensors with respect to various strategies of enzyme immobilization, e.g.. physical binding, covalent binding, gel entrapment, electropolymerization, sol-gel techniques and self-assembled architectures are also presented. The requirements and problems for sensing in food industry, examples of enzyme electrodes, published in the literature during the last half-decade. commercial biosensors released into the market along with the current and modern instrumentation, are also presented. Electroanalysis

This paper describes the monitoring of 16 polynuclear aromatic hydrocarbons (PAH) in the suspended particulate matter in the area of Ioannina. A total of 244 samples were collected from five locations throughout the city. These samples were analyzed in order to acquire a complete picture of the PAH abundance and distribution above the city of Ioannina. The sampling sites covered the center of the city as well as the suburban territory. The monitoring lasted for one year starting in November 1996. Higher values of PAH were found at the sites surrounding the city center, while at the rest of the area the concentration of PAH was substantially lower. The effect of ambient temperature and humidity on PAH abundance and distribution was also evaluated. As a result it was revealed that higher concentrations of PAH are favored by low temperatures and high values of humidity. Regarding the seasonal variation of PAH it was found that their concentrations are elevated during the winter months where heating systems are operating. On a daily basis it appears that the highest abundances of PAH occur on Wednesdays while the lowest on Sundays. The mean yearly concentration values of benzo[a]pyrene varied between 0.32+/-0.02 and 2.63+/-0.08 ng m(-3) for the various sites. Compared with the reported values the PAH levels in the area of Ioannina can be characterized as medium to low. (C) 2002 Elsevier Science B.V. All rights reserved. Talanta

The development of 1-(2-pyridylazo)-2-naphthol (PAN)-modified polymeric membranes for the effective batch pre-concentration and determination of zinc traces with flame atomic absorption spectrometry (FAAS) is described. The method is based on the chemical bonding of the metal species with a suitable ligand, which has been immobilized into a water-insoluble cellulose acetate (CA) membrane followed by simple rinsing of the chelating agent-metal complex with an acidified methanolic solution. The latter is directly aspirated to the nebulizer of a FAA spectrophotometer without any other treatment. As an analytical demonstration, trace concentrations of Zn(II) were successfully detected in real samples, such as seawater, river and take water, wastewater as well as in a reference material, without any laborious and time-consuming treatment. Several working parameters were investigated. A pre-concentration factor of 100 was achieved by simple immersing of a circular piece of the CA-PAN membrane (0.6 cm diameter) in the tested samples for 30 min at room temperature. The analytical curve was rectilinear up to 30 mug l(-1) zinc with detection limit of 0.7 mug l(-1), a quantitation limit of 2.0 mug l(-1) and a relative standard deviation lower than 2%. (C) 2002 Elsevier Science B.V. All rights reserved. Talanta

Analytica Chimica Acta

Analytica Chimica Acta

A selective and sensitive method for the determination of the total amount of vanadium in nutritional and biological substrates is proposed. The method is based on the reaction of vanadium with 2-alpha-pytidylthioquinaldinamide (PTQA) in the presence of H2O2. The product of this reaction emits constant fluorescence, in a sulfuric acid environment, at 490 nm, with the exciting radiation set at 340 run. Various parameters such as acidity, flow rate, solvents, and temperature were studied. The presence of a surface-active agent was also considered in order to increase sensitivity. At the optimal conditions, a calibration curve was constructed, revealing a linear range of 2-100 mug L-1 and a detection limit as low as 0.5 mug L-1 while the RSD ranged in the area of 0.1-1.8%, depending on vanadium concentration. The method was successfully applied to the analysis of a wide variety of food samples, which are known to contribute to the dietary required amount of vanadium and to relevant biological matrixes. Reversing the conditions of the above reaction, the effect of the peroxy group on the vanadium-PTQA system was examined. The formation of a vanadyl complex was revealed which was suitable for the determination of hydrogen peroxide and peroxy acids. linear calibration curves in the range of 0.2-50 muM for H2O2 and 0.1-2 muM for a respective peroxy acid were obtained, yielding detection limits of 0.05 and 0.03 muM, respectively. Anal Chem

A method has been developed for the trace determination of two sunscreen constituents (2-hydroxy-4-methoxybenzophenone and octyldimethyl-p-aminobenzoic acid) in water samples, which are commonly used in commercial formulations. The method employs solid-phase microextraction (SPME) and gas chromatography with flame ionization and mass spectrometric detection. The technique was developed with headspace and direct sampling in order to demonstrate the applicability of these SPME extraction modes for the identification of these two UV absorbing compounds in waters. The main parameters affecting the SPME process, such as desorption time, extraction time profile, salt additives, pH, and temperature, were investigated, The poly(dimethylsiloxane) 100-mum and polyacrylate 85-mum fiber coatings were found to be the most efficient for the extraction of these compounds from aqueous matrices, Linear calibration curves in the wide range of 10-500 mug/l were obtained for both compounds yielding typical RSD values of 5-9% for both extraction modes, ne recoveries were relatively high, 82-98%, with quantitation limits below I mug/l. A comparison between the proposed methods and the conventional multiresidue solid-phase extraction revealed that the proposed technique(s) can be reliably used for sunscreen residue measurement in water samples with satisfactory results. (C) 2002 Elsevier Science B.V. All rights reserved. Journal of Chromatography A

The development of a highly sensitive method for the determination of nanomolar concentrations of hydrogen peroxide in the liquid phase is described. This paper demonstrates for the first time a flow injection analysis (FIA) system with immobilized enzyme reactor combined with a total internal reflective cell (a liquid waveguide capillary cell (LWCC)) and spectrophotometric detection, for the development of an improved procedure for the determination of hydrogen peroxide. Moreover, the newly synthesized 4-aminopyrazolone derivative, 4-amino-5-(p-aminophenyl)-1-methyl-2-phenyl-pyrazol-3-one (DAP), is used as a color coupler in its oxidative condensation with the sodium salt of N-ethyl-N-sulphopropylaniline sodium salt (ALPS) which acts as a hydrogen donor. Immobilization of peroxidase is achieved by coupling the periodate-treated enzyme to aminopropyl controlled-pore glass (CPG) beads. The determination of hydrogen peroxide is carried out in a 0.1 M phosphate buffer and the product is monitored at 590 nm with a charge-coupled device (CCD) detector equipped with fiber optics in a fully computerized system. The interference of different species, mainly ionic, was investigated. The method permits detection down to 4 nmol l(-1) hydrogen peroxide (signal-to-noise ratio = 3). A linear calibration graph was obtained over the range 20-700 nmol l(-1). The relative standard deviation (R.S.D.) at 300 nmol l(-1) H,02 is 1.7% (n = 7), The method was successfully applied for the determination of hydrogen peroxide in samples from a vat-cleaning process. (C) 2002 Elsevier Science B.V. All rights reserved. Analytica Chimica Acta

2,5-Hexanedione (2,5HD) is the principle metabolite of n-hexane and methyl ethyl ketone in human urine. In this paper, a rapid and highly sensitive method for the determination of urinary 2,5HD by gas chromatography-electron capture detection and gas chromatography-mass selective detection is described. The method comprises, optionally, acid hydrolysis before the analyte is being derivitized with 2,4,6-trichlorophenyl hydrazine (TCPH) towards the formation of a chlorinated hydrazone derivative for 2,5HD analysis. The reaction conditions such as temperature, time, reagent concentration and pH were optimized properly. The detection limit of the method - defined as signal to noise ratio = 3 - is as low as 0.4 and 1.5 muM using the ECD and MSD (SIM mode), respectively. The linearity of the detection systems extends up to 50 muM of 2,5HD with correlation coefficients better than 0.9995. The within-day and between-day reproducibility for a urine sample of 10 muM in 2,5HD were 2.6 and 3.2%, respectively. Spiked pooled samples with various concentrations in the range 5-10 muM were processed following the proposed procedure. The recovery was satisfactory enough ranging from 92 to 104%. The method was applied to the analysis of urine samples received from people working in a chemical laboratory and the results revealed variable, yet low concentrations of 2,5HD in the hydrolyzed samples. (C) 2001 Elsevier Science B.V. All rights reserved. Analytica Chimica Acta

Environmental Science and Pollution Research

The development of a chemiluminescence (CL) method based on the perm-selective properties of a Nafion-cellulose acetate (CA) composite membrane for the monitoring of nitric oxide (NO) in biological fluids is described. Horseradish peroxidase (HRP) was used as NO trapping solution, forming the stable compound HRP-NO. The HRP was denatured and the trapped NO was released and detected by using the luminol-H2O2 system. Using a mixed (size-exclusion and polar-based) transport control, the interference effects of various compounds were minimized. The method was used for NO monitoring in simulated samples, by using a blood specimen as sample matrix. The 3 sigma detection limit is 0.9 x 10(-6) mol and linear semi-log calibration plot in the range 1.8 x 10(-6) to 2.7 x 10(-3) mol NO was constructed. The applied methodology was further used to prolong the NO lifetime in order to increase the sensitivity of its determination. This was based on the increase of the response in the presence of certain reductive species, which act as NO preservatives in biological fluid samples. (C) 2001 Elsevier Science B.V All rights reserved. Analytica Chimica Acta

A novel, water-insoluble, salt of alpha -Keggin-type silicotungstic heteropolyacid with hexadecylpyridinium cation (SiW(12)Hex) was synthesized. The salt was immobilized onto the surface of spectroscopic graphite electrodes through physical adsorption from acetone solution to produce chemically modified electrodes (SiW(12)Hex-CMEs). Some preliminary electrochemical data of soluble silicotungstate salts as well as of the modified electrode are given. Parameters such as the roughness of the electrode surface, the surface coverage and pH effect were investigated. The modified electrode was employed for the amperometric detection of periodate through its electrocatalytic reduction to iodate at -0.40V (vs. Ag-/AgCl) at pH 4.5 and for the indirect determination of ethylene glycol in antifreezing fluids. Linear plots of cathodic current versus the ethylene glycol concentration in the range of 0.2-5 mM ethylene glycol were obtained. An accuracy better than 2.1% and a reproducibility (relative standard deviation) of 1.9% (n = 10) for a 5 x 10(-4) M standard solution of ethylene glycol were achieved. The recovery was 98-101 %. Electroanalysis

The catalytic effect of vanadium on the pyronine B-H2O2 system is examined. Enhancement of the catalytic reaction rate along with the efficiency and selectivity against vanadium is achieved in a formic acid environment in the presence of a nonionic surfactant (Triton X-114). Elimination of drastic interference caused by inorganic acids and aqueous matrix along with a 50-fold preconcentration of vanadium are facilitated through cloud point extraction of its neutral complex with 8-quinolinol in an acidic solution. Subsequent flow injection analysis (FIA) with fluorometric detection renders the proposed method ideal for selective and cost-effective determination of as little as 0.020 mug L-1 vanadium in environmental, biological, and food substrates. The preconcentration step can be applied simultaneously to multiple samples, allowing for massive preparation prior to analysis, compensating, thus, for the time-consuming procedure. Anal Chem

The toxicity of chromium in the environment is dependent on the species in which it exists. This paper outlines a method for the analysis of the oxidation states of Cr employing a suitable chelating agent and the cloud point phenomenon for Cr(VI) and total Cr analysis. The method involves preconcentration of metal chelates followed by air-acetylene flame atomic absorption spectrometric analysis. The chelating agent chosen for this task is the ammonium pyrrolidinedithiocarbamate, which reacts with either Cr(VI) or total Cr under specific experimental conditions. The condensed surfactant phase with the metal chelate(s) is introduced into a flame atomic absorption spectrometer, whereby discrimination of Cr species is feasible by calculating the Cr(III) concentration from the difference between total Cr and Cr(VI). A multivariate design was employed to study the variables affecting the overall analytical performance for total Cr assay. The analytical curves are rectilinear up to 100 mug l(-1) for both oxidation states of the metal. The limits of detection are 0.6 mug l(-1) and the relative standard deviation (n = 5) at a concentration of 30 mug l(-1) for both species is around 2.0%. The method was validated by analysing BCR 544 reference material certified for both Cr species. High recoveries in the range 96-107% were attained for the environmental and biological samples tested. Analyst

A new method based on the cloud point extraction (CPE) technique was applied for the differentiation and the selective determination of Cr species. Cr(III) reacts with 8-hydroxyquinoline (8-HQ) in a surfactant solution yielding a hydrophobic complex, which then is entrapped 'in situ' in the surfactant micelles. The Cr(VI) assay is based on its reduction to Cr(III) by sulfite which subsequently reacts with 8-HQ in a similar manner. In order to increase the sample throughput a flow injection analysis (FIA) system allied to fluorimetric detection was employed. Using a simple FIA configuration the greatest sensitivity was obtained which under the optimum working conditions, allows the reliable determination of Cr(III) and/or Cr(VI) at levels as low as 0.2 mug l(-1),in various samples even in those with complex matrix (sea water, pharmaceuticals). The whole procedure is straightforward, without any laborious, expensive and hazardous treatment and was proved to tolerate interferences among the cations and anions tested. Moreover, the analytical approach offers distinct advantages over the commonly used analytical methods especially for large number of samples with complex matrixes, which would unavoidably require arduous and delicate pretreatment. (C) 2001 Elsevier Science B.V. All rights reserved. Analytica Chimica Acta

A preconcentration methodology utilizing the cloud point phenomenon is described for the determination of iron, cobalt and nickel by flame atomic absorption spectrometry (FAAS). The method employs the formation of complexes of the metallic species with ammonium pyrrolidinedithiocarbamate (APDC), which are subsequently entrapped in the micelles of the surfactant TX-114, upon increase of the solution temperature to 70 degreesC. The surfactant micelles, after their dilution to an acidified methanolic solution, are delivered to the nebulizer of the FAAS by a flow injection analysis (FIA) manifold, allowing for the reproducible injection of a small volume of the sample. The ability to handle the final texture of the injected solution allows for the single-step determination of these metal ions, in a single sample, without interferences. Analytical curves were rectilinear up to concentrations of 350 mug l(-1) for Fe, 200 mug l(-1) for Co and 250 mug l(-1) for Ni with detection limits of 19, 5 and 11 mug l(-1), respectively. The method was applied to the analysis of several real and spiked samples yielding satisfactory results. The recoveries obtained were in the range of 97-103% for spiked samples and 98-99.5% for a Certified Reference Material (CRM). Journal of Analytical Atomic Spectrometry

The importance of the surface coverage in the behavior of chemically modified electrodes and its effect on different electrochemical parameters such as the peak potential separation DeltaE(p), the potential of full width at half peak height E-fwhm and the apparent electrochemical rate constant k degrees, is discussed. The influence of the morphology of the surface of the electrode on the value of surface coverage is also demonstrated. Electroanalysis

In this work a kinetic spectrophotometric method for,I the determination of trace amounts of vanadium is presented. The method is based on the catalytic effect of the vanadium(V) on the reaction between diphenylamine (DPhA) and hydrogen peroxide in a concentrated solution of formic acid. The formation of the deep-blue oxidation product is followed by a filter spectrophotometer, equipped with an optical fiber assembly, on line with a PC provided with the suitable software. The measurements were taken at 583 nm, with an immersed type cell of 1 cm light path length. The optimization of the operating conditions regarding concentrations of the reagents, temperature and interferences are also investigated. The working curve is linear over the concentration range 0.40-4.0 mug/ml vanadium(Ti). The relative standard deviation for a standard solution of 0.6 mug/ml of vanadium is 0.5% (n = 5). The proposed method proved highly sensitive, selective and relatively rapid for the assay of vanadium, at low level of 0.40 mug/ml without any pre-concentration step. The method was applied to alloys and cosmetics samples. The results were compared to those received with a reference method. Good agreement was attained, with a mean error of 0.5%. Mikrochimica Acta

Glassy carbon electrodes coated with a cellulose acetate film incorporating 2,6-dichlorophenoiindophenol (CA/DCPI) were developed. At this multifunctional coating DCPI serves as a mediator for the electron transfer kinetics and in conjunction with the cellulose acetate's size exclusion properties it results in a chemical sensor with great selectivity and stability. Access to the surface can be manipulated via controlled hydrolysis of the film in KOH or ZnCl2 solutions. Different permeabilities are obtainable by hydrolyzing the him over different time periods. Diffusion coefficients D-app of these films for analytes of different molecular sizes were determined with double step chronocoulometry. The electrochemical characteristics of the immobilized DCPI were explored using cyclic voltammetry. The formal potentials of the immobilized DCPI coating hydrolyzed in KOH, ZnCl2 and with ZnCl2 in the casting solution were found to be 70, 75, and 79 mV (vs. Ag/AgCl/ 3M KCl), respectively, at pH 6.5. The dissociation constants of the DCPI redox couple were found to be 5.2 +/- 0.1 (pKr) and 7.4 +/- 0.05 (pKo). The electrochemical rate constant k(o) of the of DCPI redox couple within the film was also evaluated. The behavior of the sensor towards different reducing compounds was investigated. The sensors showed good operational and storage stability. Electroanalysis

Two kinetic approaches were applied for the simultaneous determination of cobalt, nickel, and iron with multiple linear regression (MLR) method, using the entire kinetic curves or the initial rates of the reaction. The predictive ability of MLR method is based on the slight kinetic differences of these metals which occur at a great number of wavelengths when they react with xylenol orange as a common ligand. The reactions were monitored using a charge coupled device (CCD) W-VIS spectrophotometer attached to a stopped-flow system. This instrumentation allowed to obtain kinetic data at a maximum of 2048 wavelengths simultaneously. The method was successfully applied to the simultaneous determination of these metals in alloys and the results obtained from the two kinetic approaches were compared. (C) 2000 Elsevier Science B.V. All rights reserved. Analytica Chimica Acta

The synthesis of simple, extensively conjugated chromophores as substitutes for 4-aminoantipyrine (4-AAP) capable of causing hyperchromic shifts when coupled with phenols is described. The 4-aminopyrazolone derivatives synthesised are subsequently applied for the spectrophotometric assay of phenolic compounds and the advantages of each of the proposed systems are highlighted. No improvement is made on the detection of para-substituted phenols as well as polychlorophenols (e.g. pentachlorophenol). An increase in the sensitivity of coupling products is obtained for certain phenolic compounds as indicated from the comparison of the individual responses. The proposed methods have analogous analytical features and in some cases show considerable improvements compared to the 4-AAP method. Beer's law is obeyed over a wide dynamic range (up to ca. 500 mu g/l) and the relative standard deviations are

The construction of a liquid triphenyltetrazolium cation (TT+) ion-selective electrode (ISE) based on [TT+](3)[P(W3O10)(4)] salt dissolved in 2-nitrotoluene is described. The liquid membrane electrode exhibits a rapid and almost Nernstian response to triphenyltetrazolium cations in the concentration range from 2 x 10(-4) to 1 x 10(-2) mol l(-1). The Nernstian slope is 56-58 mV decade(-1) which remains constant for at least two months. The response is virtually unaffected by pH changes in the range 3-12. Major interferents are periodate and malate. Deviation from linearity is also observed in the presence of bromide, iodide and thiocyanate, due to their precipitation with triphenyltetrazolium cations. Analytical applications such as direct potentiometry for the determination of TTS in aqueous solutions and indirect potentiometry for the assay of ascorbic acid (vitamin C) in pharmaceutical preparations are described. Ascorbic acid in the range of 150-500 mg l(-1), under specified experimental conditions, can be determined with mean relative error of 1.9%. Mikrochimica Acta

A screen printed carbon electrode (SPCE) impregnated with the electrocatalyst 2,6-dichlorophenolindophenol lanthanum salt ([DCPI](3)La) was constructed. Using cyclic voltammetry the electrochemical behaviour of SPCE, -SPEs and their catalytic effect towards ascorbic acid was investigated. A synthesis protocol ([DCPI](3)La) and some identification studies are given. The fabrication of (SPE) using a mixture of 5% (w/w) [DCPI](3)-La/graphite powder in 1 and 2% (w/v) ethyl cellulose in 2-butoxyethylacetate is also described. Constant potential amperometry in stirred solutions was used for the determination of ascorbic acid in beverages and pharmaceuticals potential of +0.1V versus Ag/AgCl, at pH 7.25 was employed. This technique was also used to assess the reproducibility of the electrode manufacture. Interference of various compounds was also studied. Good correlation with the official titrimetric method was attained. Calibration graphs were linear over the range 0.01-1 mM ascorbic acid and the RSD was 1.8% (n = 9) for 0.6 mM ascorbic acid. Recovery ranged from 91 to 103%. The [DCPI](3)-La-SPE showed very good storage and operational stability. (C) 2000 Elsevier Science B.V. All rights reserved. Analytica Chimica Acta