Electrolytic Generation of Cadmium(II) and Its Application to Coulometric Assays of Gallium and Indium

Abstract

The current efficiency for the electrolytic generation of cadmium(II) from an amalgamated cadmium anode was investigated as a function of electrolyte composition and current density. The generation of cadmium(II) proceeded with 100% current efficiency over a wide range of current density, when both sodium chloride and sodium acetate concentrations were higher than 0.1M. Thus, the use of cadmium(II) instead of zinc(II) as a coulometric titrant for complexometry (T. Tanaka et al., Bunseki Kagaku, 33, E9 (1984)) reduced the error in amperometric indication of the end point. With 0.5M sodium chloride-0.5M sodium acetate medium of pH 5.5, high-purity gallium and indium were assayed coulometrically. The method was based on the reaction of the sample metal ion with a known excess of EDTA, the unconsumed EDTA being back-titrated with electrolytically generated cadmium(II). The relative standard deviation of the results was about 0.01% for both metals in the range of 200-300mg.