Kh. Z. Brainina

Film stripping voltammetry.

Film stripping voltammetry is a new electrochemical analytical method consisting in concentrating the test substance in the form of a metal or a sparingly soluble compound on the electrode surface and subsequently recording the current for electrodissolution of the deposit. The method has been worked out for determination of metal ions, anions and variable valence ions, with sensitivities as low as 10(-9)M. As indicator electrodes, solid, usually graphite, electrodes and stationary mercury electrodes are used.

Potentiometric Study of Antioxidant Activity: Development and Prospects

The increasing interest in the study of the antioxidant activity of different objects is caused by an unbalance between the formation of reactive oxygen species (ROS) and the performance of the antioxidant system in humans under certain conditions, which leads to oxidative stress and pathological states of the organism. This article presents a brief critical review of the methods that are used to measure integrated antioxidant activity (AOA). It is shown that the most promising methods for measuring AOA are electrochemical ones, particularly potentiometry, as it best fits the nature of the processes causing oxidative stress. The article gives the theoretical rational for requirements that an oxidizer of antioxidants (AO) should meet. The work presents the thermodynamic grounds for the use of an earlier proposed mediator system, kinetics of chemical reactions between AO and the mediator system. In order to confirm reliability and accuracy of the results, numerous correlation studies were conducted, aiming to compare the data obtained with the use the proposed method and independent analytical methods. The article presents the results of the potentiometric study of AOA for a variety of objects, including individual antioxidant → nutritional supplements → food → blood and blood fractions.

A chronoamperometric method for determining total antioxidant activity

A novel version of a chronoamperometric method of antioxidant determination is described. It is based on the use of the oxidation current of ferrocyanide formed in the reaction of antioxidants to be determined with potassium ferricyanide as an analytical signal. So the total concentration of all antioxidants present in the analyzed solution, i.e., total antioxidant capacity, is measured. The results of blood plasma analysis by the newly presented and certified potentiometry method are in good agreement with each other, R2 = 0.9980. The detection limit makes 2 × 10−6 M for uric and ascorbic acids and 5 × 10−6 M for cysteine and glutathione.

Inverse voltammetry of antimony with triphenylmethane dyes

A method is suggested for the determination of traces of antimony by inverse voltammetry of the solid phases formed with triphenylmethane dyes (Crystal Violet, Methyl Violet and Malachite Green) as the precipitants. The authors have studied the effect of concentration, adsorption and oxidation of the triphenylmethane dyes, potential and time of pre-electrolysis, and concentration of antimony(III) and some other elements on the polarogram shape and stripping current. A method for determining antimony traces in chromic salts is described as an example.

The effect of the system polydispersity on voltammograms of nanoparticles electrooxidation

The paper proposes a mathematical model describing electrooxidation of a polydisperse system of metal nanoparticles from the surface of an indifferent macro-electrode. It is shown that the degree of dispersion of a nanoparticle ensemble affects the shape of oxidation voltammograms. When the degree of dispersion rises and the average size of nanoparticles becomes smaller, the range of oxidation potentials increases. The results of the experimental study of electrooxidation of gold nanoparticles with different degrees of dispersion are given. The particles were localized on the surface of graphite screen-printed electrodes. A good agreement between the parameters of the experimental and calculated voltammograms confirms the correctness of the proposed model.

Advances in voltammetry.

The possibilities of voltammetry as a source of information in bioelectrochemistry, electro-chemistry solid-state chemistry and analytical chemistry are reviewed. Attention is drawn to the use of catalytic currents and adsorption, inverse voltammetry, and solid and modified electrodes. The review mainly covers papers published in 1983 and 1984, especially those in the Soviet literature.

New Analytical Applications for Sodium Diethyldithiocarbamate

Abstract The electrochemical behavior of sodium diethyldithiocarbamate has been studied. A method has been developed to determine trace amounts of the reagent by preparatory electrolysis at a suitable potential which causes the sparingly soluble electrochemical product to precipitate on a small graphite electrode. The inverse polarogram gives a current which can be evaluated quantitatively, produced by the re-dissolving of the film on the electrode. Sodium diethyldithiocarbamate can also be used for electrochemically concentrating cobalt in the form of a sparingly soluble compound of Co(III) by measuring the current required to reduce (re-dissolve) the compound. The electrochemical oxidation reaction of sodium diethyldithiocarbamate to give insoluble films could be used for indirect determination of the metal ions which interact with the reagent.

Mathematical modeling and experimental data of the oxidation of ascorbic acid on electrodes modified by nanoparticles

Physical and mathematical models are proposed which describe the electrochemical transformation of compounds diffusing from the solution to an ensemble of nanoparticles (i.e., nanoelectrodes), located on a solid bulk electrode surface. Electrochemical oxidation of ascorbic acid at solid electrodes (glassy carbon, Graphite Ultra Trace and gold) unmodified and modified with gold nanoparticles (Aunano-ensemble of nanoelectrodes) was experimentally studied. Nanoeffects and diffusion limiting current were observed in the investigation of ascorbic acid oxidation on Aunano electrodes. Nanoeffects manifested themselves in a shift of the oxidation potential towards negative values with decreasing size of the nanoparticles. Agreement between theoretical and experimental results was demonstrated. The shift of the peak potential or half-peak potential can be used to estimate the size of nanoparticles and Gibbs free surface energy and contribution of nanoeffects to the kinetics of the electrode process.

Potentiometry for the determination of oxidant activity

This paper aims to describe a new approach to using potentiometry for determining oxidants in liquids and ozonized and chlorinated water, in particular. The source of information is the electrode potential shift of the mediator system observed when an analyzed sample, containing oxidants, is inserted into an electrochemical cell. Criteria for the selection of the mediator system for oxidant determination are proposed. Potassium ferri/ferrocyanides serve as the mediator system in the proposed method. K3[Fe(CN)6] is chosen as the model oxidant. Special attention is focused on the role of the state of an indicator electrode surface and ways of its regeneration in generating an analytical signal. The information is essential for obtaining correct results in different areas of electrochemical analysis. As a result, a simple, fast, sensitive, and reliable method that does not require the use of reference solution is proposed, which ensures its advantages over other methods. The accuracy and reliability of the data obtained are confirmed by the analysis results received by using the standard method.

Determination of urea and creatinine by chronoamperometry

AbstractsMethods are developed for the non-enzymatic chronoamperometric determination of urea in blood serum and creatinine in model solutions imitating the composition of blood serum. The selectivity of determination is ensured using columns packed with an anion-exchange resin for urea or synthesized molecularly imprinted polymers for creatinine.