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.