256 IODINE 



by external measurement, (e) metabolic concentration of iodine which 

 permits therapeutic applications. Preparation 1-13 1-P offers the advan- 

 tage of freedom from radiocontamination which will usually offset the 

 slightly higher cost. Direct gamma counting of tissue samples is usually 

 preferred, since this eliminates the necessity of ashing, handling proce- 

 dures, and self-absorption corrections. The amount of xenon daughter 

 produced is very small and can be neglected for practical purposes. A 

 comparison has been presented of the relative effectiveness of nine 

 methods of detection (1-2). The values are in general agreement with 

 those listed above. In addition, it is pointed out that liquid samples can 

 be counted with beta or gamma tubes usually with 0.1 to 0.01 of the effec- 

 tiveness of other methods. These procedures are useful for measurement 

 of urines, etc., which may contain relatively high levels. 



Chemistry. It is usually desired to estimate total inorganic and 

 protein-bound iodine in biological tissues, particularly thyroid gland and 

 plasma. The classical procedure (1-3) consists in digestion of the organic 

 tissues, plasma, or protein precipitate with a mixture of chromic and 

 sulfuric acids which oxidizes iodine to nonvolatile iodic acid. The latter, 

 plus the excess chromic acid, is reduced with phosphorus acid, and the 

 volatile iodine formed is distilled and trapped in an alkaline solution. 

 The iodine is then measured by its catalytic effect on the reduction of 

 eerie sulfate by arsenious acid. A simplifying modification has been 

 described in which the oxidation and digestion are accomplished by chloric 

 acid, thus avoiding the need for special distillation apparatus (1-4, 1-5). 

 The protein is precipitated with trichloroacetic acid, and the usual ceric- 

 arsenious system is used for evaluation of iodine. Another simplified 

 method has been described which consists in ashing the thyroid glands 

 with KOH, taking up the ash in water, acidifying, and then oxidizing with 

 bromine to yield soluble iodate salts that are determined colorimetrically 

 (1-6). Thyroxine has been estimated by extraction with butyl alcohol 

 from an alkaline hydrolysate, followed by conventional iodine determina- 

 tion (1-7). 



In P^^ studies, aliquots of the fractions separated in the above analyt- 

 ical procedures can be used for radioactivity measurements. In a study 

 of various tissue digestion procedures for radioassay, the following method 

 appeared to give the best recoveries: Weighed portions of the tissue were 

 placed in 50-ml centrifuge tubes, and a mixture of 2 A'' NaOH, 0.1 ml of 

 0.5 M Nal, and 0.1 ml of 0.5 M NaHSOs was added (1-8). The tissue 

 samples were incubated overnight at 70°C. Obviously on account of the 

 volatility of iodine, one must be sure that the ashing or digestion proce- 

 dure employed does not cause losses. 



Typical Methods. In this laboratory the following dosages have been 

 administered intraperitoneally or intravenously to permit external count- 



