Separation of Free Iodides from Iodotyrosines of Serum and Thyroidal Extracts by Means of Modified Charcoal

BLAU'S modification1 of the Leland and Foster2 method for separation of free iodides and iodotyrosines from thyroxine in n-butanol extracts has constituted the cornerstone of blood butanol-extractable iodine methods3,4 and facilitates the quantitative analysis of thyroxine in thyroid extracts1. The complete fractionation of iodinated compounds, however, requires the use of lengthy techniques of column or paper chromatography; the latter is not always easy to quantitate and is subject to considerable experimental error. Block et al.6 indicated that activated charcoal can quantitatively separate iodinated amino-acids from inorganic iodide, but fortunately no experimental details were given. We consequently worked out a method whereby Blau's alkaline reagent, containing iodide and iodotyrosines washed out of butanol extracts, is treated with modified charcoal to quantitatively adsorb the iodotyrosines and thus separate them from free iodide. The method is simple and is applicable to both chemical as well as to radioisotope studies.