SPECTROPHOTOMETRIC DETERMINATION OF THIOSULFATE

Abstract

For the determination in small amounts of thiosulfate, advantage is taken of the fact that when a mixture of iron(III)/1.10-phenanthroline is added to a solution containing thiosulfate ions a stable orange-red colour, due to the formation of iron(II)/(1.10-phenanthroline complex, is produced. Thiosulfate reacts with the equimolar amounts of iron(III) in acidic medium. The effective molar absorptivity for thiosulfate is 1.1 X 10(4) M-1 cm-1. Max. absorption is at 510 nm and Beer's law is valid below the concentration of 1.2 X 10(-4) M S2C32-. The method can be applied to the determination of thiosulfate in the range 9.10(-7) - 1.2 x 10(-4) M.