V. A. Tarasova

Voltammetric determination of thallium(I) at a mechanically renewed Bi-graphite electrode

A composite of high-purity grade carbon powder and an epoxy resin is used to in situ obtain a bismuth-film electrode. The surface of the indicator electrode is renewed by cutting a thin surface layer before each determination. The in situ obtained Bi-film electrode is virtually no different from an Hg-film electrode in sensitivity, reproducibility, and the ability to separate signals from Tl, Cd, and Pb. The calibration graph is linear in the range of thallium concentrations from 0.01 to 1 mg/L (RSD varies from 4 to 2%). A significant excess of Pb(II), Sn(II), and Cd(II) does not interfere with the determination of thallium. A procedure for determining down to 5 × 10−6% thallium in lithium carbonate is developed.

Voltammetric Determination of Maleic and Fumaric Acids at an In Situ Renewed Graphite Electrode

It was shown that a graphite electrode renewed by cutting a thin surface layer immediately before each measurement can be used for the voltammetric determination of maleic and fumaric acids. The mechanical renewal of the electrode by polishing did not give a reliable signal. The relative standard deviation in the determination of maleic and fumaric acids at the in situ renewed graphite electrode was 3–6%, and the detection limits for both acids were 0.4 mg/L. The deaeration of the solutions is not needed before the determination, which increases the rapidity of the method.

High-voltage electrodeposition conditions in the stripping voltammetry of metal ions: A mechanism and analytical prospects of the process

It was found that the exaltation phenomenon in the parallel reduction of hydrogen ions from weak acids or water is responsible for the acceleration of the electrodeposition of metals under high-voltage conditions. Under these conditions, the rate of electrodeposition can be increased by 2 to 3 orders of magnitude compared to the rates of electrodeposition under standard conditions. At a constant high voltage of electrodeposition, the stripping peak currents of metals are proportional to the deposition time and the bulk concentration of analyte ions. Exaltation phenomena can be used in analysis not only for intensifying the process, but also for lowering the limit of detection, improving the selectivity, and decreasing the adverse effect of surfactants.

Exaltation effects in the metal electrodeposition from acid electrolytes

The exaltation of mass transfer of discharging cations, caused by the concurrent hydrogen evolution from acidified solutions, results in a sharp increase in the metal deposition rate. In this case the limiting process rate depends linearly on the hydrogen evolution current density; it depends but weakly on the solution agitation and temperature. Under the electrolysis of solutions containing weak acids as a supporting electrolyte, the higher the acid formation constant, the more pronounced is the dependence of the electrodeposition limiting rate on the hydrogen current density. When microelectrodes are used, the varying of the background acid nature may affect the hydrogen evolution rate markedly, while the metal electrodeposition rate mainly depends on the cell voltage. When metals are electrodeposited from complex anions, the parallel hydrogen evolution hinders the mass transfer; this process depends on the anion stability constant and charge, all other conditions being the same. The found peculiarities can be used in the inversion voltammetry for the lowering of the metal detection limit, improving of the analysis selectivity, and time saving.