Biexponential model for the kinetics of the substitution reaction in the radioimmunoassay of triiodothyronine

Abstract

The influence of initial concentrations, ionic strength, viscosity and temperature on the substitution reaction of 125I‐triiodothyronine (T3) (M) by unlabelled T3 (Q) in the immunocomplex PM (P = anti‐T3 antibody) has been studied, and a kinetic model is proposed. The apparent rate constant is dependent on the initial concentration of labelled and unlabelled T3, viscosity and temperature, and independent of ionic strength. The reaction is endothermic and is not controlled by diffusion. The results obtained are in line with the proposed model. We propose some modifications for optimizing the technique.