Appendix X L. Oxidising Substances

Transfer 4.0 g to a glass-stoppered, 125 mL conical flask and add 50.0 mL of water R. Insert the stopper and swirl for 5 min. Transfer to a glass-stoppered 50 mL centrifuge tube and centrifuge. Transfer 30.0 mL of the clear supernatant liquid to a glass-stoppered 125 mL conical flask. Add 1 mL of glacial acetic acid R and 0.5 g to 1.0 g of potassium iodide R. Insert the stopper, swirl, and allow to stand for 25 min to 30 min in the dark. Add 1 mL of starch solution R and titrate with 0.002 M sodium thiosulfate until the starch-iodine colour disappears. Carry out a blank determination. Not more than 1.4 mL of 0.002 M sodium thiosulfate is required (0.002 per cent, calculated as H₂O₂).

1 mL of 0.002 M sodium thiosulfate is equivalent to 34 µg of oxidising substances, calculated as hydrogen peroxide.