Determination of Micro Amounts of Polythionates. X. Spectrophotometric Determination of Micro Amounts of Pentathionate in Mixtures with Thiosulfate and Sulfite by Means of Its Sulfitolysis

Abstract An accurate method has been proposed for the determination of pentathionate in mixtures with thiosulfate and sulfite. The method is based on the formation of thiosulfate equivalent to the pentathionate, and the spectrophotometric determination of excess iodine for the reaction with the thiosulfate formed. The conditions for pentathionate to be quantitatively converted into thiosulfate were established by varying pH, reaction time, and amounts of sulfite. The method can be successfully applied to the determination of pentathionate, thiosulfate, and sulfite when they are mixed in various ratios, giving a relative standard deviation of 0.82% at the 0.5 μmol level of pentathionate in a 10.0 cm3 sample solution in the presence of 0.5 μmol of thiosulfate and 0.25 μmol of sulfite.