Determination of thyroid hormones in serum by means of a cation exchange resin and chloric acid digestion

A simple and specific method for the determination of iodoamino acids (IAA) and hormonal iodine (HI) in serum is presented. 0.5 ml serum is allowed to run through a small column with a cation exchange resin. To isolate IAA, the column is washed with water and eluted with ammonia. To isolate HI, the column is washed with borate buffer, then with water and eluted with ammonia. After removal of the ammonia by heat, the organic iodine compounds are digested with chloric acid. Iodine is assayed by eerie sulphate-arsenious acid colorimetry. Normal values for IAA ranged from 3.6 to 7.2 μg iodine/100 ml serum (mean value 5.10 μg iodine/100 ml), and for HI from 3.0 to 6.0 /μg iodine/100 ml serum (mean value 4.30 μg iodine/100 ml)