N. A. Malakhova

Disposable thick film modified graphite electrodes for stripping voltammetry

Disposable thick film modified graphite electrodes (DTFMGE) are described. Disposable thick film graphite electrodes (DTFGE) are used as a substrate for DTFMGEs. Insoluble inorganic mercury salt, organic insoluble complexes or soluble compounds protected with Nafion were used to modify electrode surface. That provides the possibility to determine Pb, Cd, Cu ions concentration without using metallic mercury and its soluble salts and to eliminate the need for mechanical surface regeneration. As to their characteristics, these electrodes differ little from the usual ones which are coated with mercury either beforehand or in situ. Test concentrations of Me2+ were: 1μg 1−1Cd(II) + 2.0 μg 1−1Pb(II) + 5 μg 1−1Cu(II) in one series of the experiments, 2 μg 1−1Cd(II) + 4.0 μg 1−1Pb(II) in the second series and 10 μg1−1Cd(II) + 10 μg 1−1Pb + 10 μg1−1Cu(II) in the third series. Two additions were injected into electrochemical cell. The detection limit for the elements mentioned is on the sub-μg 1−1 level. Relative standard deviation is 2–5%. 0.1, 0.2 and 1 M HCl were used as background electrolytes. Results were obtained without deaeration of the solution. Well shaped peaks, stable peak increments after standard additions introduction and satisfactory correlation between added and found concentrations of metal ions during a long period of time makes the electrodes promising prospective for stripping voltammetry.

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.

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.

Solid Carbon Containing Stripping Voltammetry Sensors

Various types of carbon-containing sensors (electrodes) — glassy carbon, impregnated graphite, thick-film graphite and modified sensors — and two versions of stripping voltammetry — differential pulse voltammetry and fast linear scan response differentiation voltammetry — are described. By way of example, concentrations of Cu, Pb and Cd were determined with in situ mercury plated electrode, those of Pb and Cd on modified electrodes in the absence of metallic mercury or soluble mercury salts, and those of Cr, W and Ni using adsorptive stripping voltammetry. The fast linear scan response differentiation voltammetry is shown to have certain advantages, such as elimination of the need for removal of oxygen from the solution and well defined responses of reversible and quasireversible processes, specifically, from copper.