The test shall be carried out in diffuse daylight or in artificial light. Weigh in a glass scoop (5.1) or, failing this, in a flask (5.2), to the nearest 0,001 g, a mass of the sample in accordance with the following table, according to the expected peroxide value:
| Expected peroxide value(meq) | Weight of test portion(g) |
|---|---|
| 0 to 12 | 5,0 to 2,0 |
| 12 to 20 | 2,0 to 1,2 |
| 20 to 30 | 1,2 to 0,8 |
| 30 to 50 | 0,8 to 0,5 |
| 50 to 90 | 0,5 to 0,3 |
Unstopper a flask (5.2) and introduce the glass scoop containing the test portion. Add 10 ml of chloroform (6.1). Dissolve the test portion rapidly by stirring. Add 15 ml of acetic acid (6.2), then 1 ml of potassium iodide solution (6.3). Insert the stopper quickly, shake for one minute, and leave for exactly five minutes away from the light at a temperature from 15 to 25 °C.
Add about 75 ml of distilled water. Titrate the liberated iodine with the sodium thiosulphate solution [X1(6.4) (0,002 Mol/L solution for expected values less than 12, and 0,01 Mol/L solution] for expected values above 12) shaking vigorously, using starch solution (6.5) as indicator.
Editorial Information
Carry out two determinations on the same test sample.
Carry out simultaneously a blank test. If the result of the blank exceeds 0,05 ml of [X10,01 mol/L sodium] thiosulphate solution (6.4), replace the impure reagents.