Spectrophotometric determination of thiosulfate by its oxidation with iodate

Thiosulfate was oxidized stoichiometrically to sulfate with Iodate in a sulfuric acid medium. The produced iodine, equivalent to the excess iodate, was spectrophotometrically measured as triiodide at 350nm. The complete oxidation of thiosulfate to sulfate using iodate was achieved. The reaction rate was investigated in a medium containing varying amounts of sulfuric acid at room temperature and at 40°C. A linear calibration graph with a negative slope was obtained over the concentration range 4×10-7-4.3×10-5M (mol dm-3)(0.045-4.82ppm) thiosulfate. The relative standard deviation was 0.41% at the 2.5×10-5M thiosulfate level. The proposed method was successfully applied to the determination of thiosulfate in hot spring and lake waters.