Observations on the Separation and Measurement of Inorganic Iodine in Rat Thyroid Glands1

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Abstract
Several methods for separating thyroidal inorganic from organic radioiodine have been directly compared, and the recoveries of inorganic iodine which they afford have been assessed. Complete or nearly complete recovery of inorganic I131 was provided by paper electrophoresis, 1-hr dialysis, or acid-precipitation of thyroid homogenates. In thyroid glands uniformly labeled with I131, lowest values for inorganic I131, indicating most effective separation and/or least artifactual deiodination, were obtained with paper electrophoresis. Slightly higher values were found with 1-hr dialysis. Substantially higher values were obtained with trichloroacetic and perchloric acid precipitation, chromatography, and iodate oxidation. The greater values found with dialysis and with acid-precipitation procedures than with electrophoresis resulted from the inclusion in their presumed inorganic fraction of iodinated compounds, presumably iodopeptides, which remained near the origin of chromatograms and electrophoretograms. The greater values yielded by chromatography and by oxidation with iodate were not satisfactorily explained. Of the methods tested, direct electrophoresis of thyroid homogenates appeared the most satisfactory technique for separating thyroidal inorganic and organic iodine.