Pseudopolarography at the mercury hemisphere ultramicroelectrode: theory and experiment

Abstract

Trace heavy metals play a central role in many biogeochemical processes. Their toxicity and bioavailability in aqueous systems has been shown to be directly related to the chemical forms in which they exist, i.e., their chemical speciation. Especially promising in speciation studies has been an electrochemical technique referred to as pseudopolarography or stripping polarography. The theoretical expressions for pseudopolarography at a hemispherical mercury ultramicroelectrode are derived and compared with experimental data at varying deposition times and low and high electrolyte concentrations and with previous theory for other electrodes. It is shown that, even though several of the physical conditions are different, the behavior of both the pseudopolarographic half-wave potential and the limiting peak stripping current is similar to that for the HMDE. The fit between the theory and the experimental data was excellent. A correction term for the increase in the limiting peak stripping current with increasing negative deposition potentials seen in this and previous works is discussed and attributed to adsorption of trace organics on the mercury electrode surface. 21 refs., 4 figs., 1 tab.