A rapid method of determining total iodine in bovine milk

Abstract

One millilitre of milk is wet ashed with chromic acid to free all bound iodine and oxidise it to iodate. The iodate is then reduced to free iodine by the addition of orthophosphorous acid. The iodine is distilled and is trapped in dilute thiosulphate solution. After dilution, the iodide ion is determined by a simple colorimetric method, based on the action of tetrabase and chloramine T. The assay range is 0–200 µg of iodine per 100 ml and the colorimetric assay itself is 0–0·04 µg ml^–1 of iodine, with a sensitivity of 0·001 µg ml^–1 of iodine.