Stopped-flow--photometric and kinetic--fluorimetric methods for the determination of thyroid hormones in tablets

The catalytic effect of thyroxine and triiodothyronine on the reaction between cerium(IV) and arsenic(III) was studied by using photometric and fluorimetric measurements. The kinetic - photometric studies were based on measurement of the decrease in absorbance of cerium(IV), whereas the rate of formation of fluorescent cerium(III) was measured in the kinetic - fluorimetric studies. A modular stopped-flow system was coupled to a spectrophotometer in order to develop stopped-flow methods for the determination of thyroxine and triiodothyronine. The proposed methods were compared and applied to the determination of these hormones in pharmaceutical preparations.