Recommended procedure

Dissolve the quantity of test substance as specified in the monograph, usually about 3 g, accurately weighed, in 15 mL of chloroform R and 30 mL of glacial acetic acid R in a 250-mL glass-stoppered flask. Add 1 mL of a freshly prepared solution of 1.3 g of potassium iodide R in 1 mL of water, stopper the flask, mix by gentle swirling and set aside in the dark for 3 minutes. Add 100 mL of water, shake, and titrate with sodium thiosulfate (0.01 mol/l) VS, using starch TS as indicator. Repeat the operation without the substance being tested and calculate the difference between the titrations, the limit value being specified in the monograph.