REDUCTION OF PERTECHNETATE-99 BY STANNOUS CHLORIDE .1. STOICHIOMETRY OF REACTION IN HCL, IN A CITRATE BUFFER AND IN A DTPA BUFFER

The reduction of pertechnetate-99 by excess stannous chloride in several media was investigated as a possible model for radiopharmaceutical preparations which are based on the reduction of pertechnetate-99m by the same reagent. Polarographic and iodimetric techniques were used to analyze for unreacted stannous ion. It was found that pertechnetate is reduced to the plus 4 state in a citrate buffer at pH 7, to the plus 3 state in a DTPA buffer at pH 4, and possibly to the plus 4 state in HCl. The reaction in DTPA solution was found to be complete within several minutes. The reduction in the citrate buffer proceeded rapidly to the plus 5 state, and much more slowly to the plus 4 state. The implications of these rate studies for the radiopharmaceutical preparations are discussed. Data are presented in graphical and tabular form.