INDIRECT SPECTROPHOTOMETRIC DETERMINATION OF MICROAMOUNTS OF THIOSULFATE

Abstract

A spectrophotometric method for microdetermination of S2O32- has been developed. The method is based on the oxidation of thiosulfate with chlorine (Cl2) and the residual chlorine is determined by the color reactions with o-tolidine (3,3'-dimethylbenzidine). A linear calibration graph (0 - 8 x 10(-6) M S2O32-) is obtained under optimum reaction conditions at room temperature and pH 11. The stoichiometric mole ratio of chlorine, Cl2, to thiosulfate is 4. The effective molar absorptivity for thiosulfate with o-tolidine is 2.15 x 10(5) M-1 cm-1 at pH 1.6. The lower limit of determination is 4.65 x 10(-8) or 5.21 ppb (0.026-mu-g thiosulfate in 5 ml).