Indirect determination of traces of thiosulphate by differential-pulse polarography

Two methods are reported for the indirect determination of thiosulphate down to ca. 0.02 μg/ml by differential-pulse polarography. Both methods involve prior oxidation of thiosulphate with iodine, either in acidic medium to tetrathionate or in alkaline medium to sulphate, whereby ultimately one and eight equivalents of iodate are obtained, respectively. The concentration of iodate in the resulting solution is then measured by differential-pulse polarography under optimum conditions. The average recovery for each method amounted to 100.1%, and the relative standard deviations were 1.3 and 1.4% for the two methods.