Purification of thyroxine and triiodothyronine for radioassay with sephadex.

The use of [125I] thyroxine in the determination of dialysable thyroxine (free T4) places very high demands on the purity of the reagent. Less than 5% dissociated radioactive iodine (as iodide) is enough to influence the results [1]. For this reason several workers have developed methods for the purification of iodo amino acids used in radioassay for thyroid hormones. Two techniques have been used mainly, namely dialysis of incubated tracer-serum mixture [1,2], and adsorption chromatography on dextran gels in strongly basic buffers [3-5]. In this laboratory we have developed an adsorption chromatography method using bovine serum albumin for the separation of [125I] thyroxine from contaminating compounds.