Attila Yildiz

Electrochemical behavior of polyaniline films in acetonitrile

Abstract The electro-oxidation and electroreduction behavior of polyaniline films in acetonitrile in the absence and presence of added acid or base were investigated using cyclic voltammetry. A general mechanism is proposed that enables the interpretation of the electroactivity loss and the catalytic and autocatalytic properties of the film. The electroactivity loss was found to be a reversible phenomenon which is accelerated in alkaline solutions through deprotonation. Electroactivity was recovered when the electroinactive films were reduced in an acidic solution. The films that lose their electroactivity on electro-oxidation were found to be conducting, and various cation radicals in the structure are believed to be responsible for this nonprotonic conductivity. The proton content of the polyaniline film was found to be crucial in determining its electrochemical and physical properties. Autocatalysis was detected when protons were produced electrolytically in situ during electropolymerization.

A new amperometric enzyme electrode for alcohol determination

A new enzyme electrode for the determination of alcohols was developed by immobilizing alcohol oxidase in polvinylferrocenium matrix coated on a Pt electrode surface. The amperometric response due to the electrooxidation of enzymatically generated H(2)O(2) was measured at a constant potential of +0.70 V versus SCE. The effects of substrate, buffer and enzyme concentrations, pH and temperature on the response of the electrode were investigated. The optimum pH was found to be pH 8.0 at 30 degrees C. The steady-state current of this enzyme electrode was reproducible within +/-5.0% of the relative error. The sensitivity of the enzyme electrode decreased in the following order: methanol>ethanol>n-butanol>benzyl alcohol. The linear response was observed up to 3.7 mM for methanol, 3.0 mM for ethanol, 6.2 mM for n-butanol, and 5.2 mM for benzyl alcohol. The apparent Michaelis-Menten constant (K(Mapp)) value and the activation energy, E(a), of this immobilized enzyme system were found to be 5.78 mM and 38.07 kJ/mol for methanol, respectively.

Amperometric enzyme electrode for aerobic glucose monitoring prepared by glucose oxidase immobilized in poly(vinylferrocenium)

Abstract A simple, sensitive, stable and low-cost glucose sensor with a fast response that operates under aerobic solution conditions is described. The electrode consists of a polyvinylferrocenium-perchlorate-coated Pt surface onto which the enzyme is attached. The current response of the electrode was determined by measuring either cyclic voltammetric peak current values or steady state current values obtained after a constant-potential step. The effects of glucose concentration, the amount of enzyme immobilized, the thickness of the polymeric layer and the operating temperature on the response of the enzyme electrode were studied. The effects of two common physiological sources of interference were also investigated. A mechanism for the operation of the electrode is also proposed.

Electrochemically controlled solid-phase microextraction (EC-SPME) based on overoxidized sulfonated polypyrrole

A method for the extraction and selective determination of cations is proposed using electro-synthesized overoxidized sulfonated polypyrrole film. The polymer film is used for the selective extraction of trace levels of nickel and cadmium ions by solid-phase microextraction (SPME). The cation uptake and release properties of the overoxidized sulfonated polypyrrole film electrode were examined under both open circuit and controlled potential conditions for prospective applications in electrochemically controlled solid-phase microextraction. Increased extraction efficiency and selectivity toward cations were achieved in high saline content of water. Simple preparation of film coatings on a platinum wire was possible using a constant potential method. Applied positive and negative potentials facilitated the extraction and desorption of cations, respectively. Nickel and cadmium ions were desorbed into sample aliquot and determined by electrothermal atomic absorption spectrometry (ETAAS). The cation uptake and release mechanism is affected both by the cation exchange at the negative sulfonate and carboxylate moiety on the film and the altered solution pH occurring at the counter electrode caused by the applied potential. The method was validated using a standard reference material and tested for the determination of cadmium ion in commercial table salt samples.

Amperometric enzyme electrode for sucrose determination prepared from glucose oxidase and invertase co-immobilized in poly(vinylferrocenium)

Abstract Co-immobilization of two enzymes, glucose oxidase and invertase, in polyvinyl(ferrocenium) perchlorate (PVF + ClO − 4 ) film led to the development of a simple, sensitive, stable and low-cost sucrose sensor. Invertase catalyses the conversion of sucrose to α-glucose and β-fructose. Phosphate ions used in the medium catalyse the conversion of α-glucose to β-glucose, eliminating the need for the commonly used third enzyme, mutarotase, for mutarotation. Glucose oxidase catalyses the oxidation of β-glucose to gluconic acid, producing H 2 O 2 . Current due to H 2 O 2 oxidation catalysed by PVF + centres was measured, in contrast to most existing sucrose electrodes, which rely on measurement of the O 2 reduction current.

Investigation of some parameters influencing electrocrystallisation of PbO2

Abstract Optimum electrocrystallisation conditions of PbO2 have been investigated in acetonitrile by controlling experimental parameters such as water content, current density, electrolyte concentration, and acidity. It was determined that the crystallinity, conductivity and β-content of PbO2 films are highly dependent on these factors and that electrodeposition solution, which has 6 M water, 0.1 M lead perchlorate and no acid, gave the best crystalline PbO2 with 99% of β form. The conductivity value of this film was 6028 S/cm. All analyses were confirmed by XRD method

A new amperometric enzyme electrode for galactose determination

Abstract A new enzyme electrode for the determination of galactose was developed by immobilizing galactose oxidase in polyvinylferrocenium matrix coated on a Pt electrode surface. The amperometric response of the enzyme electrode was measured at a constant potential of +0.70V vs SCE. The effects of galactose concentration and temperature on the response of the enzyme electrode were investigated. The response time was found to be 30–40 s and the upper limit of the linear working portion was found to be 40.0 mM galactose concentration.

The effect of monomer and acid concentrations on electrochemical polyaniline formation in acetonitrile

Abstract The electro-oxidation behavior of aniline on a Pt surface in acetonitrile + tetrabutylammonium perchlorate (TBAP) solution was investigated using cyclic voltammetry. The effects of aniline concentration and the added acid were elucidated. The polyaniline films were characterized by their cyclic voltammograms in blank solution and dry conductivities were measured using the four-probe technique. As expected from the mechanism of the electro-oxidation of aniline, improvements in the quality and quantity of the polyaniline films were obtained by adding anhydrous acid to the medium. Furthermore, it was found that the concurrent generation of acid through in-situ oxidation of dissolved molecular hydrogen was the most efficient way of improving the polymer yield and properties.

Mechanism of the electroreduction of 1,1-dicyanoethylene derivatives

The electroreduction behaviour of some substituted 1,1-dicyanoethylene derivatives in acetonitrile was investigated. The mechanism for the electroreduction of different substituted compounds was proposed using the results of cyclic voltammetry, rotating disc voltammetry, dc and differential pulse polarography and controlled potential electrolysis experiments. The effect of the presence of protons on the mechanism was also elucidated. The products of large scale electrolysis experiments were identified by the aid of electroanalytical and chromatographic methods.

Amperometric enzyme electrode for organic peroxides determination prepared from horseradish peroxidase immobilized in poly(vinylferrocenium) film

Organic peroxides, t-butyl hydroperoxide, 2-butanone peroxide, cumene hydroperoxide and t-butyl peracetate, were determined by an amperometric enzyme electrode. The enzyme electrode was prepared through electrostatic immobilization of horseradish peroxidase (HRP) in a polyvinylferrocenium (PVF) film. A PVF(+)ClO(4)(-) film was coated on a Pt foil at +0.70 V by electrooxidation of polyvinylferrocene in methylene chloride with 0.1 M tetrabutylammonium perchlorate (TBAP). The enzyme modified electrode PVF(+)HRP(-) was prepared by anion-exchange in a solution of HRP(-) in 0.05 M phosphate buffer at pH 8.5. FTIR spectroscopy was used to identify PVF, PVF(+)ClO(4)(-), and PVF(+)HRP(-). The immobilized amount of the enzyme in the film was determined by UV spectroscopy. The effects of the polymeric film thickness, bulk enzyme concentration used in the immobilization treatment and the temperature on the performance of enzyme electrode were investigated. The inhibitory effect of oxygen was also examined. Linearities, lower detection limits, active life times and sensitivities of the electrode were determined for each peroxide.