The estimation of iodine in biological materials: a modification of the method of Ellis & Duncan

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Abstract
The method of Ellis and Duncan (1953) for the estimation of protein-bound iodine in serum has been extensively modified and applied to the estimation of iodine in natural waters, milk and urine. Factors which were found to be relevant were the temperatures during digestion, the quantities and types of the reagents added during distillation and the nature of the reagents used for trapping the distilled iodine. The iodide obtained on distillation was determined by a modification of the method of Lein and Schwarz (1951), which rests on the catalytic action of iodide on the reduction of Ce4+ ions by arsenious acid. The reduction was measured spectrophotometrically at 363 mu and the reaction was carried out at room temperature. Chloride and bromide were without effect on the estimation of iodine, even when the ratio of chlorine or bromine to iodine exceeds 1.5 x 106 to 1. Concentrations less than 50 [mu]g of fluoride/10 ml did not interfere with the spectrophoto-metric estimation of iodide. The recovery of iodine, added as iodide, from an aqueous solution of potassium iodide (200 [mu]mg of iodide in 50 ml of solution) was 90% S. D. 6.2 (8 estimations). Five determinations on a sample of cow''s milk gave a mean of 9.3 [mu]g of iodine/kg of milk, S. D. + 3.7; 10 determinations on another sample of milk gave a mean of 28.9 [mu]g of iodine/kg of milk, S. D. 2.6. The mean recovery of iodine from milk samples was 96% (16 estimations). The mean iodine content in a 3 ml sample of human urine was 106 [mu]mg, S. E. M. 2.9 (9 estimations), and the mean percentage recovery of iodine from urine was 89.8% (8 estimations). The mean recovery of 131I-radioiodinated protein-bound iodine from serum was 85% (11 estimations).

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