2 COLORIMETRIC ASSAYS FAR IODINE IN FOODS

Using a standardized sample preparation, comparisons were made of two colorimetric iodine assays that are based on different chemistry. One assay kinetically measured the initial iodine catalysis of the redox r eaction between Ce+4 and As+3. The other monitored iodine catalysis of the reaction between thiocyanate and nitrite by measuring light absor bance after 20 min. Both were accurate when tested with reference samp les of nonfat milk powder and oyster tissue that had known certified i odine content. The thiocyanate-nitrite assay consistently showed great er precision and less variability, particularly at lower iodine concen trations in lyophilized egg samples.