Effect of electroactive substances forming water-soluble reduced species on the potentiometric stripping determination of mercury soluble metals

When localized regions with high concentrations of water-soluble reduced species are formed during the electrolysis period of potentiometric stripping analysis, the stripping signals arising from oxidation of amalgamated metallic analytes are overlapped by interfering signals. Dissolved reduced species may give rise to plateaux on the potential vs. time curve. If the re-oxidation of such reduced species is governed by transport, plateaux are developed at the equilibrium potential of the soluble redox system, while an anodic translation of plateaux is observed when the re-oxidation is kinetically controlled. These effects complicate the potentiometric stripping determination of, for example, cadmium and lead in complex samples such as decomposed, dissolved fly ash. This paper deals with the mechanisms leading to interference. It is shown that increased transport rates induced by vigorous stirring eliminate the interference problems.