Spectrophotometric determination of trace amounts of sulphide and hydrogen sulphide by formation of thiocyanate

Abstract

The formation of thiocyanate was achieved by the oxidation of sulphide with iodine in the presence of cyanide; the thiocyanate formed was measured spectrophotometrically as the iron(III)-thiocyanate complex. The hydrogen sulphide, separated from other sulphur anions such as polythionates, was introduced into a solution containing iodine, cyanide and buffer, in which the hydrogen sulphide was completely converted into thiocyanate. A linear calibration graph was obtained over the range 1 × 10^–5–6 × 10^–4M sulphide (3.2–192 µg of S^2– in 10 ml) and the relative standard deviation was 0.37% at the 4 × 10^–4M sulphide level. The proposed method was applied successfully to the determination of sulphide in natural water samples at various concentrations.