A method is described for the quantitative determination of 131I-triiodothyronine and 131I-tetraiodothyronine in human plasma after oral administration of 131I-iodide.
Steps in the method are: acidified n-butanol extraction of the thyroid hormones from the plasma deprived of inorganic iodine by means of an ion exchange resin; addition of stable iodo-aminoacid carriers to the butanol extract and its evaporation to dryness under reduced pressure; bidimensional thin layer chromatography of the rediluted extract on cellulose in combined organic alkaline and organic acid systems; staining of the carriers with eerie sulphate-sodium arsenite reagent and diluted methylene blue; radioactivity measurements of the cellulose scraped from the stained spots in a well type scintillation counter.
The reliability of the method was established by recovery experiments and by duplicate chromatography of plasma to which mixtures of 131I-T3 and 131I-T4 and 131I-iodide were added. Its specificity was confirmed by autoradiography. Good agreement was found with the results yielded by simultaneous paper chromatography of the same extracts. The method requires smaller amounts of plasma and allows quicker determinations than paper chromatographic procedures. Relative determinations of 131I-T3 and 131I-T4 are reported in some euthyroid and hyperthyroid patients given therapeutic and diagnostic doses of 131I-iodide.