CATHODIC STRIPPING VOLTAMMETRY OF HGSE

The problem with the presence of several cathodic stripping peaks for HgSe in acidic Se(IV) solutions has been addressed using linear sweep, cyclic, square-wave and differential pulse stripping voltammetry at a hanging-mercury-drop electrode (HMDE). When very small amounts of sel enium are accumulated, the selenium is dissolved in the HMDE and a sin gle cathodic stripping peak is obtained. The solubility of selenium in mercury was estimated to 1-2 nmol cm(-3). The deposition of larger am ounts of selenium gives rise to up to three film stripping peaks, most probably because of the reduction of thin two-dimensional and thicker three-dimensional HgSe islands formed simultaneously on the mercury s urface. In the presence of Cl-, a single narrow HgSe film stripping pe ak is observed after deposition at a potential close to the positive p otential limit of the electrode. The different voltammetric stripping techniques have been evaluated with respect to sensitivity and applica bility. At low selenium concentrations, when the selenium is dissolved in the mercury electrode, square-wave or differential pulse stripping voltammetry is the method of choice. At higher concentrations, when m ost of the material is present as HgSe, linear sweep voltammetry is th e most reliable technique.