1989 Volume 38 Issue 12 Pages 724-728
High-precision coulometric titration was developed for accurate evaluation of the deviation from stoichiometry of gallium arsenide crystal. Gallium(III) was allowed to react with a definite and excess amount of previously assayed EDTA, and the excess portion of EDTA was back-titrated with cadmium(II) ion generated electrolytically from an amalgamated cadmium anode. Arsenic(V) was reduced to the trivalent state with sodium sulfite by heating at about 40°C. The arsenic (III) was then titrated with electrogenerated iodine. The end points of the titrations were detected amperometrically. A high-purity arsenic metal was first assayed and the optimum conditions for determining arsenic were decided. Slight deviation from stoichiometry was confirmed in four gallium arsenide crystals. The standard deviations obtained by the proposed methods were of the order of 10-410-5 as an atomic fraction.
