Determination of Ascorbic Acid by Electrocatalytic Response of an Electrode Coated with Polyvinylpyridine Film and Palladium-Plated

A procedure was developed for analysis of ascorbic acid with a carbon glass electrode coated with a palladium-modified poly(2-vinylpyridine) film.     

Electrocatalytic Response of a Glassy-Carbon Electrode Modified with a Polyvinylpyridine Film with Electrodeposited Palladium in the Oxidation of Oxalic Acid

The electrochemical properties of a glassy-carbon electrode modified with a polyvinylpyridine film with electrodeposited palladium were studied. Conditions were selected for preparing a composite film on a glassy-carbon surface. It was found that palladium particles deposited on the polyvinylpyridine film exhibited electrocatalytic activity in the oxidation of H₂C₂O₄. Compared to an unmodified electrode, the oxidation potential of oxalic acid decreased and the current of its oxidation multiply increased. The catalytic current of oxalic acid oxidation was a linear function of its concentration in the range from 1 × 10^–2 to 1 × 10^–6 M.     

Voltammetry of a Benzoquinone–Hydroquinone Redox Couple at Electrodes Modified with a Polyvinylpyridine Film Doped with Cobalt Phthalocyanine

The electrochemical properties of a glassy-carbon electrode coated with a polyvinylpyridine film doped with incorporated cobalt phthalocyanine were studied in a reaction involving a benzoquinone–hydroquinone redox couple. It was found that poly-(2-vinylpyridine) film applied to the electrode and cobalt phthalocyanine deposited onto it or incorporated in the polymeric film exhibited electrocatalytic activity on the oxidation of hydroquinone. Conditions were selected for obtaining a polyvinylpyridine film doped with cobalt phthalocyanine on the electrode surface providing a maximum catalytic effect. The current of the hydroquinone oxidation peak and the current of the reverse benzoquinone reduction peak at the chemically modified electrode were linear functions of their concentrations in the range from 1 × 10^–6 to 1 × 10^–3 M.     

Electrocatalytic oxidation and flow-injection determination of sulfur amino acids on a glassy carbon electrode modified by a nickel(II) polytetrasulfophthalocyanine film

The electrochemical oxidation of sulfur amino acids, i.e., cysteine, cystine, and methionine, is studied on a glassy carbon electrode modified by a film of nickel(II) polytetrasulfophthalocyanine (poly-NiTsPc). Poly-NiTsPc demonstrates a selective mediator activity in the oxidation of sulfur amino acids, depending on the pH of solution. The proper conditions for fabricating a polymer film on the surface of glassy carbon are found and the conditions of registering the maximal electrocatalytic effect on the modified electrode are determined. A procedure is proposed for the voltammetric determination and amperometric detection of cysteine, cystine, and methionine on an electrode coated by a poly-NiTsPc film under the conditions of flow-injection analysis (FIA). The linear relation of the electrocatalytic response of a composite electrode to amino acid concentration is observed to the level n × 10^?6 M in the static mode and n × 10^?9 M under FIA conditions.     

Electrocatalytic Oxidation of Hydroquinone and Pyrocatechol at an Electrode Modified with a Polyvinyl Pyridine Film with Electrodeposited Rhodium and Its Use in the Analysis of Pharmaceuticals

The electrochemical properties of a glassy-carbon electrode modified with a polyvinyl pyridine film with electrodeposited rhodium were studied. It was found that the electrodeposited rhodium particles exhibit electrocatalytic activity in the oxidation of hydroquinone and pyrocatechol. The catalytic effect manifested itself as a multiple increase in the saturation current of an organic compound. The modified electrode was used for determining adrenalin, noradrenaline, and dopamine bearing a pyrocatechol fragment in their structure in pharmaceuticals.     

Determination of biogenic amines from electrocatalytic responses of graphite electrodes modified with metallic osmium or an osmium oxide-ruthenium cyanide film

Particles of osmium or an inorganic polymeric film of osmium oxide-ruthenium cyanide (OsO-RuCN) electrodeposited on glassy carbon (GC) electrocatalyze the oxidation of dopamine (DA), adrenaline (AD), and noradrenaline (NAD). It is found that these biogenic amines are determined with a high sensitivity by oxidation at an electrode with an OsO-RuCN film. Procedures for the voltammetric determination of DA, AD, or NAD at a composite film electrode are developed. The currents of the substrate oxidation are linear functions of the concentrations in the ranges from 5 × 10^?7 to 1 × 10^?3 M for DA and from 1 × 10^?6 to 1 × 10^?3 M for AD and NAD.     

Voltammetric and flow-injection determination of carbohydrates using composite electrodes based on carbon nanotubes and Nickel(II) hexacyanoferrate

The catalytic activities of oxo and hydroxo forms of nickel(II) on the surface of a nickel deposit and an inorganic film of nickel(II) hexacyanoferrate(III) (NiHCF) electrodeposited on a glassy-carbon electrode both unmodified and modified by multi-wall or single-wall (also functionalized) carbon nanotubes in the electrooxidation of glucose, sucrose, and maltose are compared. A more pronounced catalytic effect was obtained in the electrooxidation of these carbohydrates on an electrode modified with functionalized singlewall carbon nanotubes and a NiHCF film. Methods are proposed for the voltammetric and flow-injection determination of carbohydrates on this composite electrode. A linear dependence of the analytical signal on the analyte concentration was observed in the range from 5 × 10^?7 to 5 × 10^?2 M under stationary conditions and from 0.003 to 0.3 μmol under flow conditions.     

Inversion-Voltammetric Determination of Heavy Metal Ions on Electrodes Modified with Mono- and bis-N-Thiophosphoryl Thiourea

A method is proposed for determining Ni^{2 +}, Co^{2 +}, Cu^{2 +}, Cd^{2 +}, and Pb^{2 +} ions by inversion voltammetry on carbon-paste electrodes modified with N-diisopropoxythiophosphoryl-N'-phenyl thiourea and its derivatives: N,N'-bis-(diisopropoxythiophosphorylamidothiocarbonyl)-1,5-diamino-3-oxapentane, N,N'-bis- (diisopropoxythiophosphorylamidothiocarbonyl)-1,8-diamino-3,6-dioxaoctane and N,N'-bis-(diisopropoxythio- phosphorylaminothiocarbonyl)-1,10-diaza-18-crown-6.     

Electrocatalytic Oxidation of Ethanol on Graphite Electrodes Coated with a Nafion Film with Incorporated Particles of Ruthenium or Its Complexes

The electrochemical behavior of ethanol on graphite electrodes with a Nafion film containing ruthenium as a crystalline metal deposit or a metal complex was compared. It was found that, in the oxidation of ethanol, aqua and phenanthroline complexes of ruthenium(III) incorporated in the Nafion film exhibit catalytic activity. A larger catalytic effect was observed at an electrode containing the Ru(phen) ₃ ³⁺ complex. A procedure is proposed for the voltammetric determination of ethanol at this electrode.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 6, 2005, pp. 603–609.Original Russian Text Copyright © 2005 by Shaidarova, Gedmina, Chelnokova, Budnikov.Presented at the VI All-Russian Conference (with International Participation) on Electrochemical Methods of Analysis (EMA-2004, Ufa, May 23–27, 2004).     

Electrochemical behavior and voltammetric determination of cysteine and cystine at carbon-paste electrodes modified with metal phthalocyanines

The electrochemical behavior of cysteine and cystine on carbon-paste electrodes modified with Fe(II), Co(II), Ni(II), and Cu(II) phthalocyanines is studied. Metal phthalocyanines exhibit catalytic activity in the electrooxidation of cysteine and cystine and in the reduction of cystine. The best catalyst is the cobalt complex. In the electrooxidation of cysteine, the catalysts are electrogenerated complex species of Co(II)Pc or Co(III)Pc⁺, and in the oxidation of cystine, oxidized or reduced forms of the coordinated ligand. Various versions of the determination of cysteine and cystine by the electrocatalytic reactions on the modified electrodes are proposed.