Morphology, ionic diffusion and applicability of novel polymer gel electrolytes with LiI/I2.

Novel polymer gel electrolytes have been prepared by incorporating LiI-I(2) solutions into a polyethylene oxide matrix supported by a TiO(2) filler. The gel electrolytes, based on either acetonitrile or propylene carbonate solvents are compared with liquid standard ones and are examined by (7)Li solid state nuclear magnetic resonance relaxometry and diffusion measurements. In parallel, the triiodide apparent diffusion coefficient has been determined by linear sweep voltammetry. The results are correlated with atomic force microscopic images of the electrolytes and give insight of the dynamic properties of the ions in the constrained polymer medium. Furthermore, the dissociation of the ions is estimated by relating the ionic conductivity to the ionic diffusion. As a prime application, the polymer gel electrolytes were incorporated in dye sensitized solar cells and the measured energy conversion efficiencies were successfully correlated with their morphological, diffusive and conducting properties.

Electrocatalysis of sulphide with a cellulose acetate film bearing 2,6-dichlorophenolindophenol. Application to sewage using a fully automated flow injection manifold.

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 KCl 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 1.2% (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.

Bioelectrochemical determination of citric acid in real samples using a fully automated flow injection manifold.

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 were 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 were 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.

Determination of glycerol in alcoholic beverages using packed bed reactors with immobilized glycerol dehydrogenase and an amperometric FIA system.

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%.

Upgrade of a semi-automatic flow injection analysis system to a fully automatic one by means of a resident program.

The program and the arrangement for 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.

Spectrophotometric kinetic determination of copper(II) trace amounts based on its catalytic effect on the reaction of the reduced 2,6-dichlorophenolindophenol and hydrogen peroxide.

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.

Application of a picrolonate ion-selective electrode to the assay of calcium and piperazine in pharmaceuticals and serum.

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 in the range 3-10. Major interferents are picrates, 4-nitrophenolates, 3,5-dinitrosalicylates and 2,4-dinitrophenolates. In analytical applications direct potentiometric 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% were achieved in the analysis of pharmaceutical products.