Abstract
Lanthanum(III) has been found to catalyze the reaction of trithionate with sulfide. The effects of reaction temperature and time as well as the pH and amounts of sulfide and lanthanum(III) were investigated; the optimal conditions for trithionate to be stoichiometrically converted into thiosulfate were established. The excess sulfide used for sulfidolysis of trithionate was completely removed with a suspension of freshly precipitated zinc carbonate hydroxide. Then, the formed thiosulfate was allowed to react with a given amount of iodine; excess iodine was measured spectrophotometrically as triiodide. The proposed method was successfully applied to the determination of trithionate, thiosulfate and sulfide mixed in various ratios and gave a relative standard deviation of 1.4% for trithionate at the 1.00μmol level in the presence of thiosulfate (2.00μmol) and sulfide (1.00μmol).
