Differential pulse polarographic analysis of thyroid hormone: determination of iodine, thyroxine, and liothyronine

A differential pulse polarographic method for the analysis of thyroid and thyroid tablets for total iodine, thyroxine, and liothyronine is described. The procedure for iodine, which is also applicable to individual tablet assay, consists of ashing the sample, coverting iodide to iodate, and analyzing by differential pulse polarography. The procedure for thyroxine and liothyronine involves hydrolysis of the sample with barium hydroxide and isolation and separation of the iodoamino acids using ion exchangers, followed by differential pulse polarographic determination in a supporting electrolyte composed of 0.5 N Na2CO3 in 20% 2-propanol containing 1% tetrabutylammonium bromide. The differential pulse polarographic results for iodine agree with values obtained using the USP XIX procedure, and the quantities of thyroxine and liothyronine found agree with literature values.