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5.12 PEROXIDE VALUE

 ​           The peroxide value is the number of milliequivalents of active oxygen that expresses the amount of peroxide contained in 1000 g of the substance, when determined by the following method.

Procedure

 ​           Place about 5 g of the test substance, accurately weighed, in a 250-ml glass-stoppered conical flask. Add 30 ml of a mixture of 30 volumes of glacial acetic acid and 20 volumes of chloroform, shake until dissolved and add 0.5 ml of a saturated solution of potassium iodide. Shake for exactly 1 minute, add 30 ml of water and titrate slowly, shaking continuously, with 0.01 M sodium thiosulfate VS until the yellow colour almost disappears. Add 5 ml of starch TS and continue the titration, shaking vigorously, until the blue colour just disappears. Repeat the operation without the test substance.

 ​           Calculate the peroxide value from the expression:

where V = difference, in ml, between the titrations,

 ​            M = molarity of 0.01 M sodium thiosulfate VS, and

 ​           W = weight, in g, of the test substance.

 ​           The volume of 0.01 M sodium thiosulfate VS used in the blank determination must not exceed 0.1 ml.