N. Yu. Stozhko

Ceramic composite electrode for the determination of selenium(IV) by stripping voltammetry

A ceramic composite electrode for the determination of selenium(IV) was manufactured using solgel and screen-printing technologies. This electrode exhibits a higher sensitivity and selectivity in comparison with the other studied carbon-containing electrodes. The effect of the type and amount of graphite powder, modifier, catalyst, and pore-forming agent on the properties of the ceramic composite electrode was investigated. It was found that an increase in the pore size in the electrode reduced the selectivity of selenium(IV) determination. The calibration plot was linear over the range 0.1–20 μg/L at an accumulation time of 10 s. The relative standard deviation for the determination of 1.0 and 0.05 μg/L of selenium(IV) (n = 5) was 3% and 8%, respectively. The detection limit of selenium(IV) was 0.02 μg/L at an accumulation time of 90 s. The results of selenium(IV) determination in natural and mineral waters are presented.

A voltammetric sensor on the basis of bismuth nanoparticles prepared by the method of gas condensation

A procedure is developed for the immobilization of bismuth nanoparticles prepared by the method of gas condensation on inert supports manufactured by the screen printing method using carbon-containing inks. The electrochemical behavior of the immobilized bismuth nanoparticles is investigated, and the conditions of their electrochemical activation are found. The composition of the modifying suspension “bismuth nanoparticles-liquid” is optimized. The elaborated thick-film carbon-containing electrode modified by bismuth nanoparticles is shown to be similar in its analytical parameters to the commercially available thick-film carbon-containing electrode premodified by calomel, and substantially exceeds carbon-containing electrodes with electrolytically deposited bismuth films in its properties. The limits of detection for heavy metals by stripping voltammetry are as follows (μg/L): 0.38 for Zn(II), 0.40 for Cd(II), and 0.55 for Pb(II) at the preconcentration time 180 s.

A Sensor for the Determination of Electropositive Elements

An electrochemical sensor, namely, a graphite thick-film electrode modified with Au(III) was proposed for the determination of Hg, As, Se, and Cu. The detection limits for mercury and arsenic using the new sensor are 0.005 and 0.1 μg/L, respectively.

Surface Microreliefs and Voltage-Current Characteristics of Gold Electrodes and Modified Thick-Film Graphite-Containing Electrodes

The surface microreliefs and voltage–current characteristics of gold electrodes and modified thick-film graphite-containing electrodes were studied. The relationship between the formation of an analytical signal of mercury(II) and the surface microrelief was determined. It was found that the surface of a modified graphite-containing electrode is a self-organizing ensemble of microelectrodes.

A Thick-Film Carbon-Containing Electrode Modified with Formazan for Determining Copper, Lead, Cadmium, and Zinc

The electrochemical behavior of some hetarylated formazans introduced into the bulk of carbon-containing inks of thick-film screen-printed electrodes was studied. The compositions of complexes formed at the electrode surface were found, and their stability constants were estimated. It was shown that the modification of a carbon-containing thick-film electrode with 1-(o-chlorophenyl)-3-phenyl-5-(6-methyl-4-oxo-pyrimidinyl-2)formazan improves its sensitivity, lowers detection limits for Pb(II), Cu(II), Cd(II), and Zn(II), and ensures high precision of the results of analysis.

Thick-Film Graphite-Containing Electrodes for Determining Selenium by Stripping Voltammetry

Three types of thick-film graphite-containing electrodes were proposed for determining selenium(IV) by stripping voltammetry. Their advantages over the widely used gold-film, glassy-carbon, and impregnated graphite electrodes were demonstrated. Optimum conditions for determining selenium(IV) were chosen. Procedures for determining selenium(IV) in drinking, natural, and waste waters were developed using different sample preparation techniques.

Electrodes in stripping voltammetry: from a macro- to a micro- and nano-structured surface

A correlation between the morphology of the solid surface and electrochemical response was found in microscopic and electrochemical investigations. A shift of the oxidation potentials of metals to more negative values was observed on electrodes with microstructured surface with respect to similar processes on macrostructured electrodes. The formation of passivating films, causing reverse current and deteriorating the analytical signal, was not observed, and the performance characteristics of voltammetric procedures were improved. The experimental data indicated the increased electrochemical activity of modifying metal particles with a decrease in the particle size. As a result of the deliberate change of the surface composition and the formation of a micro- and nano-structured surface, a new generation of electrodes was developed with excellent electroanalytical characteristics.

A thick-film graphite-containing electrode modified with formazan for determining manganese in natural and drinking waters by stripping voltammetry

A mercury-free thick-film graphite-containing electrode modified with formazan is proposed for determining manganese(II) by cathodic stripping voltammetry. The detection limit for manganese(II) found with this electrode is 0.04 µg/L at a preconcentration time of 60 s. The analytical signal from manganese(II) is a linear function of its concentration in the range 0.1 to 30 µg/L. The results of determining manganese in natural and drinking waters are presented.

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.

Mathematical modeling and experimental study of electrode processes

The purpose of this paper is to propose mathematical modeling of different kinds of electrochemical processes. Electrooxidation of nitrite ions on some types of electrodes (glassy carbon, screen-printed carbon-containing, gold, and gold nanoparticles) and oxidation of ascorbic acid on gold electrodes nonmodified and modified by gold nanoparticles were used for the comparison of calculated and experimental data. It is shown that in each case, a specific shape of the voltammogram helps to identify the mechanism of the process. The comparison of the theoretical and experimental data shows that the process of oxidation of nitrite ions causes passivation of the electrode by adsorbed products of electrooxidation, and nanoeffects are not observed at that. Nanoeffects were observed in the oxidation of ascorbic acid on gold nanoparticles localized on gold electrode.