Detection of Thyroxine in Dietary Supplements Using an Enzyme-Linked Immunosorbent Assay

Thyroxine (T4), one of the thyroid hormones, in adulterated dietary supplements was analyzed using two different methods; enzyme-linked immunosorbent assay (ELISA) and LC/MS. To release T4 from thyroglobulin, samples were first hydrolyzed with proteolytic enzyme, and then the supernatant was diluted and directly analyzed using a commercial free T4 ELISA kit for diagnostic discrimination. In contrast, T4 was extracted with ethyl acetate from the supernatant, and then ethyl acetate layer was evaporated. The residue was dissolved in the mobile phase and analyzed by LC/MS with electrospray ionization (ESI) interface under positive ion mode. These methods were applied to the analyses of 13 dietary supplements advertised as weight reducers. T4 was detected in four of the samples and the analytical results by ELISA agreed well with those obtained by LC/MS. The ELISA technology described here is available for the screening of T4 in adulterated supplements.