Electrocatalytic oxidation and flow-through injection determination of cysteine with a glassy carbon electrode modified with gold-iridium binary system

Electrocatalytic activity of gold and a gold-iridum binary system electro deposited onto the surface of a glassy carbon in oxidation of cysteine was studied. A method for flow-through-injection determination of cysteine was developed.     

Electrocatalytic Determination of Oxalate Ions on Chemically Modified Electrodes

The electrocatalytic activity with respect to oxalate ions of spongy osmium immobilized within a carbon-paste electrode was studied. A procedure is proposed for electrocatalytic determination of oxalate ions on a chemically modified electrode based on spongy osmium under conditions of flow-through-injection analysis.     

Selective voltammetric and flow-injection determination of guanine and adenine on a glassy carbon electrode modified by a ruthenium hexachloroplatinate film

An inorganic film of ruthenium hexachloroplatinate (RuPtCl₆), deposited on the surface of a glassy carbon electrode, exhibits electrocatalytic activity in the oxidation of purine bases, such as adenine and guanine. Appropriate working conditions are found for fabricating a polymer film on the surface of glassy carbon and for recording the maximum electrocatalytic effect for the modified electrode. A method is developed for the selective voltammetric determination of guanine and adenine in their simultaneous presence on an electrode modified by a RuPtCl₆ film. A procedure is proposed for the amperometric detection of purine bases with this modified electrode under the conditions of flow-injection analysis. The dependence of the analytical signal on the concentration of guanine and adenine is linear up to 5 × 10^?6 and 5 × 10^?7 M in the stationary mode and to 5 × 10^?7 and 5 × 10^?8 M under flow conditions, respectively. The proposed method was tested in the analysis of calf thymus DNA for the concentrations of guanine and adenine.     

Flow-injection and sequential injection determination of hydroxypurines on an electrode modified with mixed-valence ruthenium and iridium oxides

Mixed-valence ruthenium (RuO _x ) and iridium (IrO _x ) oxides and composites on their basis (RuO _x -IrO _x or IrO _x -RuO _x ) electrodeposited onto the surface of a glassy carbon electrode exhibit a catalytic activity in the electrooxidation of uric acid, xanthine, and hypoxanthine. The transition from metal oxides to composites of two mixed-valence metal oxides leads to an increase in the catalytic effect of the oxidation of hydroxypurines. The IrO _x -RuO _x composite demonstrated the highest catalytic activity. Procedures for the amperometric detection of hydroxypurines on this composite electrode under the conditions of flow-injection analysis (FIA) and sequential injection analysis are proposed. A linear dependence of an analytical signal on the analyte concentration is observed in the range 1 × 10^?6 to 5 × 10^?3 M for uric acid and xanthine and 5 × 10^?7 to 5 × 10^?3 M for hypoxanthine under FIA conditions and from 5 × 10^?7 to 5 × 10^?3 M for uric acid and xanthine and 5 × 10^?9 to 5 × 10^?3 M for hypoxanthine in sequential injection analysis. Under FIA conditions, the sensitivity, rapidity, and performance of the analysis increase compared to the stationary conditions. The advantages of sequential injection analysis over FIA include a lower consumption of the supporting electrolyte; the absence of pumps and connections; and an increase in sensitivity, reproducibility, and rapidity.     

Joint voltammetric determination of dopamine and uric acid

Electrocatalytic activities of gold particles deposited onto an electrode unmodified and modified with a self-organized monolayer of cystamine in oxidation of dopamine and uric acid were compared. The possibility of joint determination of dopamine and uric acid on an electrode modified with self-organized monolayer of cystamine with gold nanoparticles was examined.     

Flow-Injection Amperometric Determination of DOPA and Tyrosine at a Dual Electrode Modified with the Gold–Cobalt Binary System

The gold–cobalt binary system, electrodeposited on the surface of a screen-printed electrode, exhibits catalytic activity in the electrooxidation of DOPA and tyrosine. The catalytic effect is shown in a multiple increase in current compared with the oxidation current of the modifier and a decrease in the oxidation overvoltage of organic compounds. Methods for the flow-injection amperometric determination of DOPA and tyrosine at the proposed modified electrode are developed. The simultaneous amperometric determination of DOPA and tyrosine at a dual screen-printed electrode modified with an Au–Co binary system the under conditions of flow-injection analysis is demonstrated. The linear dependence of the analytical signal on the concentration of DOPA and tyrosine is observed in the ranges from 1 × 10^–9 to 1 × 10^–4 M and from 5 × 10^–8 to 5 × 10^–4 M, respectively.     

Amperometric detection of hydroxypurines at an electrode modified with a composite based on mixed-valence ruthenium and cobalt oxides in flow injection analysis

A composite material based on mixed-valence ruthenium and cobalt oxides, electrodeposited on the surface of a screen printed electrode, exhibits high catalytic activity in the electrooxidation of uric acid, xanthine, and hypoxanthine. Catalysis manifests itself as a decrease in the substrate oxidation overvoltage and an increase in current at the potential of modifier oxidation. A method is proposed for the simultaneous amperometric detection of two-component systems uric acid–xanthine, xanthine–hypoxanthine, and uric acid–hypoxanthine using a screen printed electrode with two working electrodes modified by this composite. The dependence of the analytical signal on the concentration of analytes is linear in the range 5 × 10^–8 to 5 × 10^–3 M for uric acid and xanthine and from 5 × 10^–7 to 5 × 10^–3 M for hypoxanthine.     

Electrocatalytic Response of Electrodes Modified with Metal Phthalocyanines in the Cholinesterase–Thiocholine Ester System

Hydrolysis products in the cholinesterase–thiocholine ester system were determined by voltammetry using electrodes modified with metal phthalocyanines (MPc, M = Fe, Co). Specific features of the electrooxidation of the hydrolysis product (thiocholine) at a carbon-paste electrode and at a chemically modified electrode (CME) were compared. The conditions for the detection of an electrocatalytic signal in the oxidation of thiocholine at the CME were studied. Performance characteristics of the electrocatalytic determination of thiocholine at the CME were determined. The use of electrodes chemically modified with MPc reduces the detection limit for cholinesterase substrates under consideration to n × 10^–6 M.     

Electrocatalytic oxidation and voltammetric determination of dopamine on a composite film electrode with an iridium deposit

Electrochemical oxidation of dopamine on a composite glassy carbon electrode with an electrodeposited iridium layer coated with a Nafion film was studied. A procedure for voltammetric determination of dopamine on the composite film electrode was developed.     

Electrochemical Properties of Crown-Containing N-(Thio)phosphoryl(thio)ureas and Their Complexes with 3d Transition Metals

The electrochemical behavior of crown-containing N-(thio)phosphoryl(thio)ureas and their complexes with 3d transition metals was studied by dc voltammetry on a graphite electrode in acetone. Crown-containing N-(thio)phosphoryl(thio)ureas are not reduced but are oxidized on solid electrodes in the examined range of potentials; the electrons are transferred via the (thio)urea group. Electrooxidation of macrocyclic Co(II), Ni(II), and Cu(II) complexes probably occurs via formation of M(III) complex species. Electroreduction of these metal complexes involves stepwise electron transfer, with the oxidation state of the metal atom decreasing to 0, followed by dissociation of the electrochemical reaction products.