STRIPPING ANALYSIS AT MERCURY MICROELECTRODES IN THE ABSENCE OF SUPPORTING ELECTROLYTE

Anodic stripping voltammetry of cadmium and lead in pure water, of conductivity as low as 0.6 muS, was studied at a mercury microelectrode obtained by ex situ deposition of mercury on a 10-mum radius platinum disc electrode. The anodic stripping peaks were investigated in detail to verify the influences of the solution resistance and migration on peak position (E(p)), peak width at half-height (W1/2) and peak current. The results showed that the presence of a small ohmic drop leads to larger W1/2 values than those obtained in the presence of supporting electrolyte, while the peak position varied slightly as a consequence of a change in the liquid junction potential. For concentrations of the metal ion higher than 0.1 muM, a contribution due to migration added to the diffusion current when the samples were examined in the absence of supporting electrolyte. The results were also compared with theoretical predictions; in particular, the effects of migration were studied and transferred to a quantitative basis.