Influence of Sn2+ concentration on complexation of 99m Tc with potassium sodium hydroxyethylidenediphosphonate

Abstract

Kinetics of formation of a 99m Tc complex with potassium sodium hydroxyethylidenediphosphonate (KNaHEDP) was studied. Since the Tc reduction competes with the Tc reoxidation at low Sn2+/Sn4+ concentration ratio, the reaction accelerates with increasing Sn2+ concentration from 1 to 10 μg ml−1. At higher Sn2+ concentrations, Sn2+ ions have no effect on the complexation rate, since the concentration of reduced technetium becomes optimal for effective formation of the technetium complex with the ligand. More than 95% of 99m Tc is bound into the complex at the Sn2+ concentration higher than 20 μg ml−1. A high degree of Tc complexation is observed immediately after mixing the reactants and is maintained for 24 h. The rate and degree of 99m Tc complexation with KNaHEDP are independent of the ligand concentration in the reaction mixture, varied from 5 to 10 mg ml−1. At higher ligand concentration (25 mg ml−1), the rate of formation of the 99m Tc-KNaHEDP complex does not change, but its stability decreases.