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 Oxidation of Cysteine and Cystine at a Carbon-Paste Electrode Modified with Ruthenium(IV) Oxide

The electrocatalytic activity of ruthenium(IV) oxide incorporated into a carbon-paste electrode was studied in the oxidation of cysteine and cystine. The oxidation potentials of the amino acids decreased and the current peaks of their oxidation increased at a modified electrode as compared to an unmodified one. Procedures for the voltammetric determination of cysteine and cystine with the use of electrodes chemically modified with ruthenium(IV) oxide were proposed.     

Electrocatalytic Oxidation and Flow-Injection Determination of Sulfur-Containing Amino Acids at Graphite Electrodes Modified with a Ruthenium Hexacyanoferrate Film

The electrochemical behavior of sulfur-containing amino acids (cysteine, cystine, and methionine) at graphite electrodes modified with a ruthenium(III) hexacyanoferrate(II) film was studied. Glassy carbon and carbon paste were used as graphite materials. The electrocatalytic oxidation of amino acids at a modified electrode resulted in a decrease in the oxidation potentials of amino acids and an increase in the currents of their oxidation peaks as compared to those observed at an unmodified electrode. The voltammetric characteristics and hydrodynamic conditions for detecting the maximum catalytic current were found. A procedure is proposed for the electrocatalytic determination of cysteine, cystine, and methionine at a carbon-paste electrode modified with an inorganic film of ruthenium(III) hexacyanoferrate(II) under the conditions of flow-injection analysis.     

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.     

Crown-Containing N-(Thio)Phosphoryl-(Thio)Ureas,their Ligand Properties and Analytical Application

Abstract

Crown-containing N-(thio)phosphoryl(thio)ureas are related to a class of NH-acids due to the presence of two acceptor-groups: (thio)phosphorylic and (thio)acylic. In agreement with structure of lariat ether, it was observed a stage corresponding to the step ejection of two H* ion on the potentiometric titration curve of ligand by alkaline. Calculated step ionization constants demonstrate that these compounds are weak acids with relative values of pK₁ and pK₂.     

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.     

Chemically modified electrodes based on noble metals,polymer films,or their composites in organic voltammetry

The review deals with the current state of and prospects for the use of electrodes modified with noble metals, polymer films, or composites on their basis, which yield catalytic response in voltammetry. Techniques of applying noble metals, polymer films, or their composites to a conducting support are considered. The catalytic properties of immobilized redox mediators and the analytical, operating, and performance characteristics of this type of modified electrodes are compared.