Spectrophotometric determination of sulfide, sulfite, thiosulfate, trithionate and tetrathionate in mixtures

The proposed method consists of five procedures: the thiocyanate formed from the hydrogen sulfide evolved in Procedure 1 and an excess of iodine for reaction with the sulfur dioxide evolved in Procedure 2 are measured; the thiosulfate in Procedure 3 and the thiosulfate, plus that formed from tetrathionate by its sulfitolysis in Procedure 4, and finally an excess of iodate for the oxidation of thiosulfate, trithionate and tetrathionate in Procedure 5, are all measured by spectrophotometry. Procedure 1 can be applied to the determination of up to 6 × 10–4 mol l–1 of sulfide, Procedure 2 for up to 2.4 × 10–4 mol l–1 of sulfite, and Procedure 3 for up to 4.8 × 10–4 mol l–1 of thiosulfate. Procedure 4 is for the measurement of up to 4.8 × 10–4 mol l–1 of the total amount of thiosulfate plus tetrathionate, and Procedure 5 determines up to 4.5 × 10–5 mol l–1 of the total thiosulfate, trithionate plus tetrathionate. The method can be successfully applied to the determination of sulfide, sulfite, thiosulfate, trithionate and tetrathionate mixed in various amounts. The relative standard deviations, based on eight replicate analyses of a 10 ml solution containing a mixture of 1.0 µmol of sulfide, sulfite, thiosulfate, trithionate and tetrathionate, were 1.5, 1.2, 1.1, 1.9 and 1.1% for sulfide, sulfite, thiosulfate, trithionate and tetrathionate, respectively. Good recoveries of thiosulfate, trithionate and tetrathionate from hot-spring and lake water samples, to which various known amounts of thiosulfate, trithionate and tetrathionate had been added, were achieved with an average recovery of 98.9%.