Radioiodination of human calcitonin using the Iodogen reagent

A method is described for the radioiodination of human calcitonin using the Iodogen reagent. The tracer was purified by 2 successive gel filtrations. The first, using Sephadex G-10, resulted in the complete removal of free 125iodide as assessed by ascending paper chromatography. The second, involving Sephadex G-75, permitted the separation of the tracer from high molecular weight aggregates. Analytical RP-HPLC showed a slight proportion (13%) of a contaminating product, probably (sulfoxyl-methionine9)calcitonin. The final yield, after radioiodination, was found to be 42.7 +/- 5.5% and the tracer displayed a specific activity of 850 +/- 110 Ci/mmol. The effects of long-term storage of the frozen tracer were studied.