A simple method for the determination of iodine in the chick thyroid.

In the routine thyrotropin assay based upon the depletion of iodine in the chick thyroid gland following thyrotropin injections, a rapid micromethod for the determination of iodine was desirable. Elmer (1) gives an excellent critical review of the existing methods for iodine determination up to 1936. Kirk (2) reviews the present methods and techniques for microanalysis, including iodine. The methods (3-5) entailing distillation of iodine followed by an eventual titration with sodium thiosulfate and methods (6, 7) consisting of distillation of iodine and its eventual determination by calorimetric means proved to be too time-consuming. The catalytic or ceric sulfate method (8-lo), although extremely sensitive, is likewise too lengthy. Consequently the method of Astwood and Bissell (II), which is a modification of that of Kendall (12, 13), was further modified. This method consists of ashing the thyroid glands with potassium hydroxide, dissolving the ash in water, acidifying the solution, and finally oxidizing it with bromine to yield soluble iodate salts, the concentration of which is determined calorimetrically. This simplified procedure has made it possible for one person to run at least thirty iodine determinations per day.