Electrochemical reduction of Tc(VII) on a mercury electrode in alkali solutions

Reduction of Tc(IV) in 0.1-4.0 M NaOH was studied by tast polarography and differential pulse polarography on a stationary dropping mercury electrode and by cyclic voltammetry on a suspended mercury drop, At NaOH concentration from 0.1 to 2.0 M the polarograms contain two reduction waves I and II at halfwave potentials from -0.775 to -0.705 and from -1.07 to -1.00 V (vs, Ag/AgCl), respectively. The ratio between the limiting currents of waves II and I decreases with increasing NaOH concentration in the solution. Wave II disappears in 4 M NaOH. Technetium(VII) reduction described by wave I is irreversible and is controlled by diffusion. Wave II is of adsorption nature. As calculated by logarithmic analysis of the tast-polarographic waves and peaks of the differential pulse polarography, the number of electrons involved in the electrode reaction in 0.1 and 4 M NaOH is 1.05 and 2.5, respectively, These values determined by the Cottrell's equation are 3.24 and 2.44, respectively, The difference indicates that electrolytic reduction of Tc(VII) involves disproportionation of Tc(VI) and Tc(V), Technetium(VII) can be determined by the differential pulse polarography with a detection limit of 10 mu g l(-1) in alkali solutions containing nitrate, nitrite, and carbonate ions and containing no chromate ions which are reduced at the potentials close to the reduction potential of Tc(VII