Analytical procedure
To 50 Ml of the sample is added either 4 Ml of peroxodisulphate solution or 0.2 ml of sulphuric acid (reagent 1. see) and 220± 20 mg of solid potassium persulphate. Dissolve the reagent by swirling. Close the bottles and place them in the autoclave. Which has been filled with about 200 ml of water. Autoclave the samples for 30 min. Cool to below 50 °C and decompress the autoclave carefully, because the inner pressure of the hot sample bottles may pop the caps (if polyethylene or polypropylene bottles are used, do not decompress the autoclave before the content has cooled to room temperature ). After opening, check that the stoppers are tight the volumes of the samples are unchanged.