Use of a Dual Coulometric-Amperometric Detection Cell Approach in Thyroid Hormone Assay

Abstract

The development and application of a dual (in series) coulometric-amperometric thin-layer electrochemical detection cell system to the assay of thyroid hormones following reversed-phase chromatography is described. Using this approach the system was characterized by empirically determined electrolysis efficiencies, demonstrating adherence to the diffusion-layer approximation theory. When academic mixtures of the thyroid hormones were studied, the precision of both response and relative retention data was to within 4%. With the dual-cell approach, improvements by a factor of two in the limit of detection were noted over the same system using only amperometric detection. The electrochemical behavior of these analytes in the dual-cell system was also studied. These latter experiments demonstrated that, in principle, it is possible to assay the thyroid hormones with both cells set at a potential where mass transport control obtains, analyzing the oxidation products of the first cell at the amperometric cell.