Sulphidolysis of pentathionate and spectrophotometric determination of pentathionate, thiosulphate and sulphide in their mixtures

Abstract

A spectrophotometric method has been developed for the determination of pentathionate in a mixture with thiosulphate and sulphide. The conditions for pentathionate to be stoicheiometrically converted into thiosulphate were established by varying the reaction time, pH and amount of sulphide. The excess of sulphide used for the sulphidolysis of pentathionate was removed with a suspension of freshly precipitated zinc carbonate hydroxide. The proposed method was successfully applied to the determination of pentathionate, thiosulphate and sulphide mixed in various ratios and gave a relative standard deviation of 0.89% for pentathionate at the 1 µmol level in the presence of thiosulphate (2 µmol) and sulphide (1 µmol).