A Semiautomated Nonincineration Technique for Determining Serum Thyroxine

Abstract

Abstract Thyroxine and triiodothyronine are separated from other serum iodine-con-taining constituents by column chromatography. The iodine compounds of a serum sample adjusted from pH 10 to 11 are absorbed on an anion-ex-change resin, which is washed to remove serum proteins, mono- and diio-dotyrosines, and some organic iodine compounds of exogenous origin. Thyroxine and triiodothyronine are quantitatively eluted with 50% acetic acid and then measured by the Ce+4-arsenite reaction by use of the Auto-Analyzer. The eluates are automatically added to a reaction mixture contain-ing sulfuric acid and bromate-bromide reagent. The resulting bromine inac-tivates unidentified inhibitors and enhances the catalytic activity of thyrox-ine, thus eliminating the necessity for incineration or wet-digestion. Arsen-ous acid and Ce+4 reagents are then added to initiate the iodide-catalyzed Ce+4 arsenite reaction. On passing through two 13-m glass coils at 60°C, Ce+4 in the reaction mixture is reduced to colorless Ce+3 by iodine released from the thyroxine molecule, and measured colorimetrically at 400 nm. The analytical rate is 50 specimens per hour. Recovery data utilizing is pre-sented for the chromatography steps. The total system recovery for T4 averaged 98% (range, 85 to 112%) with a precision of ±8.5%(±2 CV). Interfer-ence by 19 organic contrast media was evaluated