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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

The concept of cloud point phenomenon is used to perform metal speciation after the studied metallic forms have reacted with suitable ligands for the formation of hydrophobic complexes, which are subsequently entrapped in the surfactant micelles. As an analytical demonstration, trace concentrations of Cr(III) and Cr(VI) were conveniently detected in samples with a complex matrix, such as sea water, without any laborious and expensive treatment using flame atomic absorption spectrometry. The speciation of Cr is performed using Triton X-114 as surfactant and, as chelating agents, ammonium pyrrolidinedithiocarbamate for Cr(VI) and 8-hydroxyquinoline for Cr(III). Analytical curves were rectilinear up to concentrations of 130 mu g l(-1) for Cr(III) and 85 mu g l(-1) for Cr(VI) with detection limits of 1.4 mu g l(-1) and 0.65 mu g l(-1), respectively. The method affords recoveries in the range 96-104% and a relative standard deviation lower than 2.2%. It is proved that the method can be successfully employed as an alternative to the commonly used preconcentration and speciation analytical techniques. By selecting the appropriate complexing agent(s) other metal speciations are feasible provided that some detailed study precedes the application. Journal of Analytical Atomic Spectrometry

An ascorbate sensor based on a glassy carbon electrode modified with a cellulose acetate polymeric film bearing 2,6-dichlorophenolindophenol (CA/DCPI-CME) was constructed. The overall reaction obeys a catalytic regeneration mechanism (EC mechanism) and the electrochemical rate constant kf for the electrocatalytic oxidation of ascorbic acid was evaluated. The modified electrodes were mounted in a flow injection (FI) manifold, poised at +100 mV versus Ag/AgCl/3 M KCl at pH 6.5 and utilized for the determination of ascorbic acid in beverages and pharmaceuticals. Good correlation with a reference method was attained. Interferents of various molecular sizes were tested. Calibration graphs were linear over the range 0.02-1 and 0.1-6 mM ascorbic acid for CA/DCPI sensors hydrolyzed in KOH and ZnCl2 solution, respectively. The throughput was 25 samples per hour and the CV was for a 0.4 mM ascorbic acid solution 0.75 (n=14) and 1.2% (n=10) for CA/DCPI sensors hydrolyzed in KOH and ZnCl2 solution, respectively. The recovery was 92-110%. The sensors showed very good repeatability and operational stability. (C) 2000 Elsevier Science B.V. All rights reserved. Analytica Chimica Acta

The application of an electrochemical sensor, based on a glassy carbon electrode, modified with a cellulose acetate polymeric film bearing 2,6-dichlorophenolindophenol (CA/DCPI-CME), for flow injection analysis of sulphide, is described. The overall reaction was found to obey a catalytic regeneration mechanism (EC mechanism) and the: electrochemical rate constant k(f) for the electrocatalytic oxidation of sulphide was evaluated. The modified electrodes were mounted in a flow-injection manifold, poised at + 0.08 mV versus Ag/AgCl/3 M KCI at pH 7.25 and utilised for the determination of sulphide in urban waste samples. The proposed method correlates well with a colorimetric method. Parameters such as working pH, sample size, flow rate and temperature were studied. Interferants of various compounds normally present in real samples were also tested. Calibration graphs were linear over the range 0.02-1 mM sodium sulphide for CA/DCPI-CMEs hydrolysed in KOH for 6 min. The throughput was 25 samples per h and the R.S.D. was 1.3% (n = 7) for 0.1 mM sodium sulphide. Recoveries for spiked urban waste samples ranged from 99 to 120%. The sensor remained active for more than 2 weeks under specified conditions. (C) 2000 Elsevier Science B.V. All rights reserved. Talanta

A series of polymeric membranes have been employed as outer barriers in an amperometric malate dehydrogenase (MDH)/diaphorase (DI) or MDH/DI/NAD(+)/mediator enzyme electrode for the determination of malate in undiluted neutral or acidic media. MDH/DI were physically entrapped with NAD(+) and mediator in a mixed ester cellulose membrane. Outer membranes such as non-anionic surfactant-modified cellulose acetate/Tween-80 and unplasticised spin coated PVC/polycarbonate (PC) resin in conjunction with an ascorbate oxidase (AOD) layer were utilised. Mechanical strength, thickness studies and diffusional properties of the membranes were investigated. Hexacyanoferrate(III), 2,4-dichlorophenolindophenol (DCPI) and naphthoquinone (NQ) were tested as mediators for enzymatically produced NADH using cyclic voltammetry. Analytical utility of the sensors is demonstrated. (C) 2000 Elsevier Science B.V. All rights reserved. Analytica Chimica Acta

Pyruvate oxidase (POD), oxaloacetate decarboxylase (AOCD), and citrate lyase (CL) were coimmobilized (or immobilized separately) in a series of polymeric membranes for the construction of amperometric bisensors of pyruvic, oxaloacetic, or citric acid in concentrated samples. For oxaloacetic acid, POD, and OACD were coimmobilized on dialysis membranes and were used in a multimembrane configuration with an inner spin-coated cellulose acetate (CA) membrane modified with isopropyl myristate (IPM) and an outer diffusion restricted membrane of cellulose acetate modified with a cationic surfactant. These membranes were also tested in a POD laminate containing the cofactors FAD and TPP for monitoring the response stability with duration of exposure to an external electrolyte and found to be effective in reagentless mode, with good pyruvate response stability over 3 h without compromise of signal size. Coimmobilization of POD/OACD and CL on different types of high protein binding membrane such as mixed cellulose ester (HA) was investigated. The relative optimum concentrations of several activators (divalent cations) and cofactors such as FAD and thiamine pyrophosphate (TPP) were investigated with the probe assembled as a pyruvate biosensor. An extended linearity up to 100 mM citric acid was achieved. Electroanalysis

An enzymic method for the determination of bilirubin is described, based on the indirect electrochemical monitoring of bilirubin via its reaction with oxygen to biliverdin in the presence of bilirubin oxidase. Amperometric signals due to oxygen depletion were taken by means of an oxygen electrode incorporating an immobilized bilirubin oxidase membrane. The calibration plot shows linearity up to 2.0 x 10(-4) M. This concentration range corresponds to elevated bilirubin concentrations in adults and in newborn infants. The RSD of the method is 3.1 % (1.0 x 10(-4) M bilirubin, n = 6). The method is interference free, fast ( < 3min) and easy to perform. The membrane retains almost 80 % of its initial activity after 30 successive measurements. Electroanalysis

Ascorbic acid present in natural products is often analyzed by its reducing effect on 2,6-dichlorophenolindophenol (DCPI). In case of coexistence of Fe(II) in natural samples and if oxalic acid is used for their extraction and stabilization, a significant interference is observed. The reaction of Fe2+ with 2,6-dichlorophenolindophenol (DCPI) in acidic solutions in the presence or absence of oxalate ions was investigated. The reaction was studied with a Stopped-Flow Spectrophotometer (S.F.S) equiped with a data acquisition system, which allows the determination of initial rates and reaction rate constants. Results for the effect of the concentrations of all the reagents of the reaction are presented. During the experimental work all concentrations of the reagents were kept in such levels to make the reaction first-order in respect of DCPI. An interesting finding is, that, although Fe2+ and C2O42- ions do not react separately with DCPI (or react very slowly), they react very rapidly in mixtures and show a strong synergetic effect. The experimental data At with the mechanism of the formation of intermediates FeC2O4 and [Fe(C2O4)(2)](2-). The proposed rate law agrees with the above mechanism and the experimental results. The value k(c) = (1.6 +/- 0.2) X 10(5) M-1.s(-1) was calculated for the second-order rate constant of the reaction of FeC2O4 and DCPI. (C) 1998 John Wiley & Sons, Inc. International Journal of Chemical Kinetics

A relatively simple, sensitive, selective, automatic fluorimetric method for the simultaneous determination of chromium(III) and chromium(vr) by flow injection analysis (FIA) was developed, The method is based on the selective oxidation of the non-fluorescing reagent 2-(alpha-pyridyl)thioquinaldinamide (PTQA), which with Cr-VI yields an intensely fluorescent product (lambda(ex) = 360 nm; lambda(em) = 300 nm), Chromium(III) is oxidized on-line to Cr-VI with sodium metaperiodate and the Cr-VI is subsequently treated with PTQA, Fluorescence due to the sum of Cr-III and Cr-VI is measured and Cr-III is determined from the difference in fluorescence values. The effects of various analytical parameters, such as acidity, flow rate, sample volume, temperature, reagent concentration and interfering species, were studied. Kinetic studies using both the stopped-flow technique and the FIA procedure were utilized in order to study and optimise the oxidation conditions for Cr-III On th, basis of its oxidation efficiency. The calibration graphs were rectilinear in the ranges 0.1-10 mu g ml(-1) for Cr-VI and 0.1-1.0 mu g ml(-1) for Cr-III, The method was successfully verified by performing recovery experiments of Cr in several standard reference materials (peach leaves, sediments and tea), and it was applied to the speciation analysis of Cr-III-Cr-VI in environmental waters (mineral, tap and distilled water), a food sample (tomato juice) and synthetic mixtures. Up to 30 samples per hour can be analyzed with a relative standard deviation of about 0.1-2%. Analyst

The preparation of a 2,6-dichlorophenolindophenol (DCPI) modified graphite electrode is described. DCPI was successfully immobilized by physical adsorption onto a plain graphite electrode (DCPI-CME) and onto graphite electrodes pretreated with lanthanum nitrate (DCPI-La-CME) or thorium nitrate (DCPI-Th-CME). The electrochemical behavior of DCPI-CME was extensively studied using cyclic voltammetry. The electrochemical redox reaction of DCPI was found to be fairly reversible at low coverage with E degrees' = + 55 mV (vs. Ag/AgCl/3M KCl) at pH 6.5. A pK(a) value of 5.8 +/- 0.1 for immobilized form of DCPI is determined from the intersection of the lines in the plot E degrees' vs. pH. The current I-p has a linear relationship with the scan rate up to 1200 mV s(-1), which is indicative for very fast electron transfer kinetics. The calculated value of the standard rate constant is k degrees = 18 +/- 4 s(-1). No decrease of either the anodic or the cathodic current of the cyclic voltammogram was observed after 500 runs of successive sweeps. The influence of the morphology of the electrode surface on the electrochemical behavior of the DCPI-CME was studied and a mathematical model is proposed, which partly describes the dependence of the geometrical area of the electrode surface on the grid of the emery paper. The modified electrodes were mounted in a flow-injection manifold, poised at +60 mV (vs. Ag/AgCl/3M KCl) and a catalytic current due to the oxidation of NADH was observed reducing thus the oxidation overpotential of NADH for about 400 mV. Interference from various reductive species present in real samples was investigated. The repeatability was 1.2% RSD (n = 10 for 0.1 mM NADH). The sensor showed good operational and storage stability. Electroanalysis

Two new compounds are studied as alternatives for replacing 4-aminoantipyrine in the spectrophotometric analysis of phenols. 4-amino-1,2-diphenyl-5-methylpyrazol-3-one and 4-amino-2,5-diphenyl-1-methylpyrazol-3-one show good analytical characteristics such as sufficient reproducibility and satisfactory detection limits when used for the analysis of phenols. In addition, the proposed methods respond highly to monochloro- and dichlorophenols and are therefore more representative for the analysis of phenols of anthropogenic origin. Fresenius Environmental Bulletin

A procedure for the enzymatic determination of alpha-glycerophosphate (alpha-GP) has been developed, using an automated in-house FIA system, with immobilized glycerol-3-phosphate oxidase (GPO) on non-porous glass beads, following optimization of the immobilization and analytical parameters. Fabricated single bead string reactors (SBSR) were used in connection with the FIA system, following optimization of its parameters. The half-life of GPO-SBSR regarding reduction of the enzyme activity was found to be 110 days for its use in 20 triplicate measurements daily and storage at 4 degrees C in the appropriate buffer. The regression equation of the calibration graph for the determination of alpha-GP was: A(max) = (10 +/- 2) x 10(-4) + (22134 +/- 12) x 10(-4) (mmol l(-1) alpha-GP). The lower limit of quantitation was 0.74 mu mol l(-1) alpha-GP and the RSD of the method 0.05% (r = 0.9999). The same FIA system and procedure can be also used for the determination of the GPO activity, with the alpha-GP as substrate. The regression equation for this calibration graph was: A(max) = (23 +/- 18) x 10(-4) + (190 +/- 1) x 10(-4) (mu g ml(-1) GPO), the lower limit of quantitation was 0.782 x 10(-3) mg ml(-1) (0.782 ppm) GPO and the RSD of the method 0.53% (r = 0.9999). Serum samples obtained from hospitalized patients were deproteinized by gel filtration and analyzed under pseudo-first order conditions, at various concentrations of alpha-GP. A kinetic study of the reduction of alpha-GP in serum versus time is given and an observed reaction rate constant k(ob) = 106.5 x 10(-4) min(-1) was determined. (C) 1998 Elsevier Science B.V. Talanta

Disposal of toxic waste is emerging as a major environmental and public health concern in Greece. Much of the concern relating to this problem evolves around their storage, disposal and fate in the environment This paper presents various issues related to the generation and disposal, particularly focusing on the environmental priorities of Greek government in view of the adaptation to the European Union standards. Fresenius Environmental Bulletin

A simple, sensitive, highly selective, automatic spectrofluorimetric method for the simultaneous determination of selenium(IV) and (VI) as selenite-selenate by flow injection analysis (FIA) has been developed. The method is based on the selective oxidation of the non-fluorescent reagent 2-(alpha-pyridyl)thioquinaldinamide (PTQA) in acidic solution (1.5-3.0 M H2SO4) by Se-IV to give an intensely fluorescent oxidation product (lambda(ex) = 350 nm; lambda(em) = 500 nm). Selenium(VI) is reduced on-line to Se-IV, in a reduction coil installed in a photo-reactor, which is then treated with PTQA and the fluorescence due to the sum of Se-IV and Se-VI is measured; Se-VI is determined from the difference in fluorescence values. Various analytical parameters, such as effect of acidity, flow rate, sample size, dispersion coefficient, temperature, reagent concentration and interfering species were studied. The photo-reduction conditions were optimized, with an FIA procedure, for Se-VI on the basis of its reduction efficiency. The calibration graphs were rectilinear for 0.1-2.4 mu g ml(-1) of Se-VI and 10 ng ml(-1)-2.2 mu g ml(-1) of Se-IV, respectively. The method was applied to the determination of Se in several Standard Reference Materials (alloy, sediments and tea), as well as in some environmental waters (tap and surface water), food samples (flour and egg), a biological sample (human hair), soil sample and in synthetic mixtures. Up to 25 samples per hour can be analysed with an RSD approximate to 0.1-2%. Analyst

An enzymic method for the determination of citric acid in fruits, juices and sport drinks is proposed, The method is based on the action of the enzymes citrate lyase, oxaloacetate decarboxylase and pyruvate oxidase, which convert citric acid into H2O2 with the latter being monitored amperometrically with a H2O2 probe. The enzymes pyruvate oxidase and oxaloacetate decarboxylase mere immobilized, A multi-membrane system, consisting of a cellulose acetate membrane for the elimination of interferants, an enzymic membrane and a protective polycarbonate membrane were placed on a Pt electrode and used with a fully automated flow injection manifold. Several parameters were optimized, resulting in a readily constructed and reproducible biosensor, Interference from various compounds present in real samples was minimized, Calibration graphs mere linear over the range 0.01-0.9 mM pyruvate, 0.015-0.6 mM oxaloacetate and 0.015-0.5 mM citrate, The throughput was 30 samples h(-1) with an RSD of 1.0% (n = 8); the mean relative error was 2.4% compared with a standard method, The recovery was 96-104%, A 8-10% loss of the initial activity of the sensor was observed after 100-120 injections. Analyst

A method for the enzymatic determination of adenosine triphosphate (ATP) and glycerol has been developed, using an automated FIA system. The enzymes Glycerophosphate Oxidase (GPO) and Glycerol Kinase (GK) have been immobilized on non-porous glass beads following optimization of the immobilization parameters. The fabricated Single Bead String Reactors (SBSR) were used in connection with a FIA system, following optimization of its parameters. The half-life of GK SBSR, regarding enzyme activity, was found to be 45 days for 90 measurements of daily use and storage at 4 degrees C in the appropriate buffer. The linear dynamic ranges of the working curves for the enzymatic determinations of ATP and Glycerol, were 4-70 mu mol.l(-1) and 2-160 mu mol.l(-1) respectively. Glycerol was determined in white and red wines after a 1:5,100 dilution. Glycerol was also determined in human serum, following deproteinization of the samples by gel filtration. The low limits of quantification (4 mu mol.l(-1) ATP and 1 mu mol.l(-1) glycerol) and accuracies better than 2% for ATP and 1% for glycerol, show that the proposed method offers many significant improvements over the conventional methods. Analytical Letters

Simplex optimized methods for the determination of cadmium and lead in environmental samples by use of electrothermal atomic absorption spectroscopy (ETAAS) are presented. The optimum experimental conditions were attained by applying the composite modified simplex optimization method after considering the following variables: ramp to ashing temperature, ashing temperature, atomization ramping time, atomization temperature and modifier concentration, The way of introducing the matrix modifier in the graphite furnace is one of the most important among the numerous factors that must be considered for the development of an ETAAS method, The matrix modifier was injected into a graphite tube provided with a L'vov platform prior to the injection of the sample, leaving the modifier wet, The analytical investigations showed that the optimized systems are ideally suited to the analysis of cadmium and lead in samples of environmental origin offering good accuracy and precision. Journal of Analytical Atomic Spectrometry

A flow injection analysis system incorporating amperometric detection and enzyme reactor for glycerol determination in alcoholic beverages is described. The reactor is based on the glycerol dehydrogenase system, and the enzyme was immobilized through chemical modification on several supporting materials such as aminopropyl and isothiocyanate controlled pore glass, aminopolystyrene resin and m-aminobenzyloxymethyl cellulose. NADH, the product of the enzymatic reaction, was monitored amperometrically with a three-electrode wall-jet type flow through cell, at +0.5 V vs. Ag/AgCl. The method was evaluated in the presence or absence of potassium and the following linear dynamic ranges were found: 2 x 10(-5)-2 x 10(-4) mol l(-1) and 4 x 10(-5)-4 x 10(-4) mol l(-1), respectively. The interference effects of various compounds were also studied. The relative standard deviation was found to be better than 1.0%, (n = 6). The reactors are stable for over a period of 3 months and after about 2500 injections. Under optimum working conditions the sampling frequency was 30 samples h(-1). The successive application of the method was confirmed by comparison with a reference method. The mean relative error is 2.2% and the recovery 95-102%. Talanta

An enzymic method for the determination of L-malic acid in fruits and vegetables is described, Malate dehydrogenase (MDH) and diaphorase (DI) were co-immobilized on aminopropyl-, isothiocyanate- and N-hydroxysuccinimide ester (N-HSE)-modified controlled-pore glass, which was then used for the construction of a packed-bed reactor, MDH catalyses the reaction between malate and NAD(+) and produces NADH, which converts hexacyanoferrate(III) into hexacyanoferrate(II) in the presence of the DI, Amperometric measurements with pure graphite electrodes in a fully automated flow injection manifold were used to monitor the concentration of hexacyanoferrate(II) at +0.3 V versus an Ag/AgCl reference electrode, The electrochemical behaviour of hexacyanoferrate(III), 2,6-dichlorophenolindophenol and p-benzoquinone was tested with cyclic voltammetry. Parameters such as working and immobilization pH, flow rate, sample size, temperature and NAD(+) and hexacyanoferrate(III) concentrations were investigated, The interference of various ions, amino acids and organic acids present in real samples was also studied, The calibration graph was linear for the range 2 x 10(-5)-4 x 10(-4) mol l(-1) malate, The reactors remained active for a period of more than 3 months under specified storage conditions, The maximum sample throughput was 30 h(-1) and the relative standard deviation of the method was better than 1.5% (n = 5), The mean relative error was 4% for fruits-and 2% for vegetables, The accuracy of the proposed method was tested by comparison of the results with those obtained by a reference method. Good correlation was attained, Recovery experiments showed results between 95 and 108%. Analyst

An automatic direct spectrophotometric method for the simultaneous determination of nitrite and nitrate by flow-injection analysis has been developed. Nitrite reacts with 3-nitroaniline in the presence of hydrochloric acid (0.96-1.8 M HCl or pH 0.5-0.7) to form a diazonium cation, which is subsequently coupled with N-(1-naphthyl)ethylenediamine dihydrochloride to form a stable purple azo dye, the absorbance of which is measured at 535 nm. Nitrate is reduced on-line to nitrite in a copper-coated cadmium column which is then treated with azo dye reagent and the absorbance due to the sum of nitrite and nitrate is measured; nitrate is determined from the difference in absorbance values. A copper column incorporated into the reaction manifold before the copperised cadmium column not only improves the long-term accuracy, but also extends the life time of the copperised cadmium column. Various analytical parameters, such as effect of acidity (pH), flow rate, sample size, dispersion coefficient, time, temperature, reagent concentration and interfering species, were studied. The calibration graphs were rectilinear for 0.1-3.5 mu g ml(-1) of NO3- and 10 ng ml(-1)-2.2 mu g ml(-1) of NO2-. The method is successfully applied to some food samples (meat, flour and cheese), environmental waters (inland and surface), beer and soil samples. Up to 30 samples can be analysed per hour with a relative precision of approximate to 0.1-2%. Talanta

In the present investigation the application of the chloranilate electrode for the kinetic determination of formaldehyde in aqueous solutions is reported. This semi-automatic method is based on the known quantitative, irreversible condensation reaction of HCHO with the salt ethylenediammonium chloranilate [EnH(2)Chl]. The soluble methylenimine is produced and the reaction rate of the released chloranilate anions is monitored with a chloranilate sensing liquid membrane ion selective electrode, in a phosphate buffer of pH = 7.0. The time required for the reaction to yield a fixed amount of chloranilate ions, and therefore the potential change to reach a preselected value (Delta E = 10mV), is measured automatically and correlated directly to the formaldehyde concentration. The average error for the determination of HCHO in the range of 40 - 200 mu M in a sample of 1 ml was about 3%, with a relative standard deviation of 2%. Measurement times were in the range of 20 - 200 s. The method is simple, fast and applicable to turbid and colored samples, where spectrophotometric methods fail. The method has been applied to the determination of formaldehyde in commercial antiseptic products and pharmaceutical preparations. The results obtained with this method, compared with those taken with conventional analytical methods, are in good agreement. No significant interferences were observed from the usually coexisting substances in the formaldehyde formulations, such as methanol, ethanol, acetone, formic acid and aliphatic or aromatic aldehydes. Quimica Analitica

The program and the arrangement far a versatile, computer-controlled flow injection analysis system is described. A resident Program (which can be run simultaneously and complementary to any other program) controls (on/off, speed, direction) a pump and a pneumatic valve (emptying and filling position). The system was designed to be simple and flexible for both research and routine work. Journal of Automatic Chemistry

The complexation process of copper(II) with oxamates was followed by the use of a copper solid state ion selective electrode. The shape of the recorded potential vs. time was interpreted on the basis of the known kinetic expressions for a two step reaction, monitoring the consumption of the reagent. The potential changes of the electrode are attributed to a decrease in the copper concentration. The curves are of an exponential form with two distinct parts, the first due to the intermediate activated complex, which is produced very rapidly, and the second is due to the slow formation of the soluble chelate. The effects of various parameters are studied in relation to the retardation of the first step. The reaction rate constant k, the equilibrium constant K-* for the fist step, the stability constant K, the activation energy E(a), the change in enthalpy, and the product (pZ) of the frequency and steric factors were determined. On the basis of the above data, a mechanistic scheme for this complexation reaction is proposed. Electroanalysis

The title compound, 2C21H38N[Be(C6Cl2O4)2], contains complex anions formed by two 3,6-dichloro-4,5-dihydroxy-3,5-cyclohexadiene-1,2-dionato residues, tetrahedrally coordinating to beryllium through deprotonated hydroxy O atoms, and hexadecylpyridinium cations. The long c axis is mainly a result of the presence of the hexadecylpyridinium cations. The cation chains are parallel to the [311BAR] direction and the pyridine rings are connected to the chloranilate O atoms by hydrogen bonds. The chains are regularly ordered parallel to one another. Acta Crystallographica Section C-Crystal Structure Communications

Gel crystallisation of oxamic acid with praseodymium nitrate hexahydrate gave the title compound which has an essentially rigid sheet polymer structure comprised of fused 24-membered metallocycle rings. Upon thermal decomposition the polymer gives Pr6O11. Polyhedron

An enzymatic method for the determination of glutamic acid in food samples and pharmaceuticals is described. L-Glutamate dehydrogenase (GLDH) from beef liver was immobilized on isothiocyanate modified Controlled Pore Glass for the construction of a packed bed reactor. The NADH produced from the enzymic reaction was monitored fluorimetrically. The working curve is linear up to 200 mumol/l glutamate for an injection volume of 58 mul. The detection limit of the method is 0.3 mumol/l. The composite modified simplex was employed for the selection of the proper experimental conditions using an in-house flow injection manifold. Many interfering species and several amino acids were tested to verify the specificity of the enzyme reactor. The system works selectively for glutamic acid. The method is ideally suited to the assay of glutamic acid in a large number of samples because of its simplicity, stability and low cost. Forty-five samples per hour can be analyzed with a relative standard deviation better than 2%. The reactor is stable for a period of more than four months under specified storage conditions. The accuracy of the proposed method is tested by comparison of the results with those obtained by the official methods and the manufacturer's specifications for the analyzed samples. Good correlation was attained. Recovery experiments showed results between 97 and 104%. Talanta

Glutamate oxidase was immobilized on non-porous glass beads and glutamate dehydrogenase was immobilized on glass derivatives. These supports were employed for the construction of Single Bead String Reactors and Packed Bed Reactors, respectively, which in turn were linked to Flow Injection Analysis systems with either photometric or fluorometric detection. Analytical working curves are linear in the range 1-200 mu mol/l for packed bed reactors and 10-500 mmol/l for single bead string reactors. The samples were pretreated depending on their origin and the applied measuring system. Optimal dilution factors were established for the two techniques. Optimal dilution ratios were established and the influence of several added substances was investigated. Recovery and method comparison studies including high performance liquid chromatography verified the accuracy of the proposed methods. Results from within-day and between-day measurements gave relative standard deviations of 4.7 and 5.9% for serum samples and 2.5 and 4.0% for brain samples, respectively. European Journal of Clinical Chemistry and Clinical Biochemistry

The construction and some analytical applications of a liquid picrolonate (Picrl(-)) ion-selective electrode based on the tris(phenanthrolinato)iron(II) (ferroin) picrolonate salt, dissolved in 2-nitrotoluene, are described. The liquid membrane electrode exhibits a rapid and almost Nernstian response to picrolonate anions in the concentration range from 5 X 10(-2) to 5 X 10(-2) mol l(-1). The response is virtually unaffected by pH changes ih the range 3-10. Major interferents are picrates, 4-nitrophenolates, 3,5-dinitrosalicylates and 2,4-dinitrophenolates. In analytical applications direct potentiomctric methods for the determination of picrolonates and indirect methods for the determination of calcium and piperazine are described. calcium in the ranges 4-24 and 50-90 mg l(-1), under specified experimental conditions,can be determined with mean relative errors of 1.1 and 1.4%, respectively. The method is applicable to soluble samples, pharmaceuticals and industrial and real human serum. Piperazine in the ranges 1-10 and 13-20 mg can be determined with a mean relative error of 1.2% in soluble salts and pharmaceutical formulations, respectively. An accuracy of better than 1.5% and a reproducibility (relative standard deviation) of 0.1.% mere achieved in the analysis of pharmaceutical products. Analyst

Instrumental Neutron Activation Analysis (INAA) and Atomic Absorption Spectroscopy (AAS) were employed for the determination of total and 0.5 N HCl extractable trace elements in surface sediments from Lake Pamvotis. The application of cluster analysis to a) total concentrations, b) 0.5N HCl extractable concentrations and c) to groups of selected trace elements resulted in the separation of the sediment samples in chemical groups which were sufficient to distinguish among different trace element sources, trace the extent of the anthropogenic or geological perturbation and define the areas of the pollution background. The combination of chemical and statistical analysis was found to be a useful tool for pollution studies especially when the volume of the available data makes their interpretation difficult. Fresenius Environmental Bulletin

In the present work two new analytical methods, a gravimetric and a spectrophotometric, for the assay of piperazine free base and its soluble salts in the anthelmitic preparation ''Oxyuran'', are described. Both approaches are based on the quantitative reaction between the diprotonated cationic form of piperazine and the 3-methyl-4-nitro-1-p-nitrophenyl-5-pyrazolone (picrolonic acid), in sulfuric acid medium, leading to its sparingly soluble canary yellow salt. Both methods exhibit satisfactory levels of mean errors 1.2% and 1.7% respectively. The proposed picrolonate gravimetric method constitutes an improvement of the classical picric acid method regarding the accuracy, sensitivity and selectivity. The two gravimetric methods were compared. Good correlation was achieved, r=0.998. The improvement in sensitivity of the new spectrophotometric method is attributed to the high molar extinction coefficient epsilon(max)=18.770 mol(-1)l cm(-1) of the picrolonates at the measuring wavelength range lambda(max)=342-345 nm. Triethanolammonium-picrolonate and piperazine-diacetate were synthetized and standardized during this work. Ach-Models in Chemistry

The heavy metal distribution in surface sediments and cores from Pamvotis Lake (Ioannina) and Kalamas River of North-western Greece over a period of two years was studied. The lake admits mainly municipal and light agricultural and industrial wastes. It merges with the river via a narrow channel where the lake water is discharged. The deposited metals and the organic carbon content were determined in sediment samples taken from nineteen stations in the lake and five stations of the river. The results suggest ''anthropogenic'' influence at the coasts near the town of Ioannina and at the first station of the Kalamas river. Fresenius Environmental Bulletin

A catalytic spectrophotometric method is presented for the determination of Cu(II), based on the oxidation of the leucocompound of the 2,6-dichlorophenolindophenol (DCPI)(r), in the presence of hydrogen peroxide and the catalytic effect of Cu(II) on this reaction in ammonia-ammonium chloride buffer solution of pH 10.5. The above reaction is followed spectrophotometrically at 562 nm. The study was carried out with a filter spectrophotometer equipped with a fiber optic and an immersed type optical cell of 1 cm. The optimum operating conditions regarding concentration of the reagents involved, pH and temperature were established. The interference effect of several metallic species was also investigated. It was found that the proposed method shows fairly good selectivity and sensitivity, simplicity and rapidity compared to other kinetic methods. The working curve of the recommended reaction-rate method is linear in the concentration range 5-300 ng/ml. The relative standard deviation for a standard solution of 30 ng/ml Cu(II) is better than 2.5%. The method was applied successfully on the determination of Cu(II) in a wide variety of real samples such as alloys, pharmaceuticals, foodstuffs and environmental samples. The results were compared to those received with official methods. Good agreement was attained. Talanta

Two Ion-Selective Electrodes (ISEs), one commercial chloride ISE and one home-made chloranilate (Chl(2-)) ISE, were applied to study the alkaline hydrolysis of p-chloranil. This reaction proceeds through a very fast first step producing monochloranilate (Ch(l-)) and chloride ions followed by a slow, rate determining step, producing chloranilate (Chl(2-)) and chloride ion. Kinetic equations specific for this reaction scheme, were derived to calculate reaction rate constants from E-t curves. The potentiometric selectivity coefficient K-pot = 2.23 x 10(4) was determined for the response of the chloranilate electrode to Chl(-) anion and used for the kinetic calculations. The reaction rate constant for the slow step of the hydrolysis was found to be 0.227 M(-1).sec(-1) at 25 degrees and the activation energy 1.56 x 10(4) Cal/mol. The total potential change following the completion of the first fast step is proportional to the log C of chloranil. Concentrations of chloranil 5-500 ppm can be determined with a precision of about 2%. This potentiometric method was evaluated for the determination of chloranil in fungicide preparations (Spergon) and the results obtained were compared with those of the official iodometric method. Good agreement was found. Talanta

The kinetics and mechanism of the reactions between 4-aminoantipyrine and/or 3,5-dichloro-2-hydroxybenzenesulfonic acid with Fe2+ in the presence of H2O2 have been investigated. A differential spectrophotometric flow injection (FI) method for the determination of H2O2 has been developed, by substituting horseradish peroxidase (PO) in Trinder's reagent with Fe2+. This method has been applied to the determination of glucose in human serum, with good results, by using an enzymic reactor with immobilized glucose oxidase and an automated Fl system, after optimizing its parameters. The agreement between the results of this method with those of the routine method used by a hospital clinical laboratory for the determination of glucose in human serum was very good. The correlation line of the two methods shows a slope of 1.03 and a correlation coefficient (r) of 0.9997. The method was also applied to the determination of H2O2. The working curve, with Fe2+ as promoter, was linear for 10-400 mumol 1-1 H2O2 compared with 5-170 mumol l-1 H2O2 when PO was used. The slopes of the curves for Fe2+ and PO are 1.69 and 4.35 A l mmol-1, respectively, showing a reduced sensitivity for the proposed method compared with the PO method. Analyst

The problem of pH measurements at extreme pH values is well known. Higher pH values are obtained at pH values of below 1 because of the so-called 'acid error'. The acid error depends on various parameters and it is not always reproducible. In order to determine accurate pH values at high acidities, a kinetic study of the decomposition of 2,6-dichlorophenolindophenol (DCPI) in strongly acidic solutions was investigated by applying the stopped-flow technique. The DCPI is unstable at lower pH values (below 2) and the reaction rate constant for its decomposition in the pH range 0-2 is dependent on the pH. A good correlation between pH and the observed reaction rate constant of the decomposition of DCPI (k(ob)) was found for low pH values. The reaction rate constant, k1, was calculated by three different approaches for the evaluation of the experimental data. The weighted mean value of k1 was found to be (77 +/- 1) x 10(-3) l Mol-1 S-1, with confidence limits of 95%. A knowledge of k1 is also important in analysis as DCPI is the main reagent for the determination of ascorbic acid in acidic solutions. Analyst

An enzymic method is proposed for the determination of glutamic acid in food samples and pharmaceuticals. The method is useful in the range 0.01-0.5 mmol 1-1, with a detection limit of 0.005 mmol l-1 for an injection volume of 52 mul. L-Glutamate oxidase from Streptomyces sp. X-1 19-6 was immobilized on non-porous glass beads, and the H2O2 produced was caused to react with Trinder's reagent. Various parameters were studied for the establishment of the optimum operating conditions for an in-house flow injection manifold with a spectrophotometric detector. Many interfering species and several amino acids were tested in order to verify the specificity of the enzyme reactor. Experimental data for interfering organic and inorganic substances are reported. The system works very selectively for glutamic acid and glutamates. The method is ideally suited to the assay of glutamates in a large number of samples within a single working day, as the frequency is 40 samples h-1. The relative standard deviation is 1.8% for six assays. The immobilized reactor is stable for a long period under proper conditions of storage. The accuracy of the proposed method was tested by comparison of the results with those of the Association of Official Analytical Chemist's method and with the manufacturer's specifications for the analysed samples, where available. Good agreement was obtained. Recovery studies yielded results between 97 and 105%. Analyst

A comparative kinetic study of soluble and immobilized amyloglucosidase (EC 3.2.1.3) on non-porous glass beads, is presented with an automated Flow Injection Analysis (FIA) system, with maltose as substrate. All measurements were based on the catalytic action of the enzymes soluble or immobilized amyloglucosidase (AG), immobilized glucose oxidase (GO) and soluble horseradish peroxidase (PO). The main results of this study, are: (i) optimization of the attachment time of the glutaraldehyde during the immobilization procedure; (ii) a detailed study on the pH of immobilization, to find its optimum value for the enzyme activity, (iii) determination of the half-life of the AG SBSRs under continuous operational conditions; (iv) determination of the kinetic parameters (K(m) and A(max) of the soluble and immobilized AG with maltose as substrate and study of the ageing effects of immobilized AG on the kinetic parameters; (v) development of an analytical FIA mode, for the determination of maltose. Acta Chimica Hungarica-Models in Chemistry

In this work the reaction of cysteine (H2Q) with 2,6-dichlorophenolindophenol (D) is studied kinetically in the pH range 2.5-9.0. Taking into consideration the distribution diagrams for the species H3Q+, H2Q, HQ-, Q2- for cysteine and DH2+, DH, D- for 2,6-dichlorophenolindophenol the reaction mte constants k(i) for all possible combinations of the reacting species were determined. The maximum reactivity appears at pH 6.88 with an overall reaction constant k = 306 1.mole-1.sec-1 at 22-degrees. The effect of the concentrations of the reagents and the ionic strength on the reaction rate is also given. From Arrhenius plots an activation energy E(a) = 8.1 kcal/mole was calculated. Working curves for the determination of cysteine in aqueous solutions are also presented applying the reaction rate method. Finally the paper includes important analytical information for the calculation of the errors due to interference of cysteine by the kinetic determination of ascorbic acid, using its reaction with 2,6-dichlorophenolindophenol. Talanta

The oxidation of glucose by Fehling solution was followed by various solid-state ion-selective electrodes. The shape of the recorded potential vs. time transient curves at three different electrodes (Cu2+, Pb2+, and Ag+/S2-) was explained on the basis of the known mechanisms of formation of precipitates, the growth of crystals, and adsorption/desorption phenomena. The curves are peculiar in shape, are very reproducible, and show three distinct parts. The potential changes of the electrodes are due to the consumption of OH- during the reaction, as well as to its adsorption and desorption on the Cu2O precipitate. The effects on the values of different curve parameters of the concentrations of glucose, OH-, and K,Na-tartrate, as well as the temperature, were studied. Electroanalysis

The reduction of 2,6-dichlorophenolindophenol (DCPI) by sulphides and sulphites has been studied kinetically by the stopped-flow technique. The reaction is first-order with respect to each of the reactants. From the distribution diagrams for the species DH2+, DH and D- for DCPI and H2Q, HQ- and Q2- for sulphides or sulphites, a mechanism is proposed which suggests partial reactions of all possible combinations of the reacting species at any pH. An equation for calculation of the second-order reaction rate constants k at any pH is derived, which gives k as a function of [H+], the partial reaction rate constants and the dissociation constants of DCPI and H2S or H2SO3. Values of the overall reaction rate constants over a wide pH-range have been determined, together with values of k for all possible partial reactions. For particular pH-values the second-order reaction rate constant was determined by four different methods. Mean values of k = 251 +/- 1 and 240 +/- 1 1.mole-1.sec-1 were obtained for pH 3.15 and 4.17, respectively, for the DCPI-Na2S reaction and k = 137 +/- 1, 127 +/- 1 and 136 +/- 1 l.mole-1.sec-1 for pH 2.02, 4.25 and 5.10, respectively, for the DCPI-Na2SO3 reaction. From the slopes of the linear Arrhenius plots activation energies of 6.6 +/- 0.2 and 4.0 +/- 0.1 kcal/mole for the DCPI-Na2S and DCPI-Na2SO3 reactions, respectively were calculated. The effect of ionic strength on the reactions supports the proposed mechanism. Talanta

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