Use of high performance liquid chromatography for the structural identification of technetium-99m radiopharmaceuticals at the NCA level.

Technetium-99m (99mTc) complexes of dithiooxalate (dto) and maleonitriledithiolate (mnt) were prepared by ligand substitution of 99mTcNCl4-, dithionite reduction of 99mTcO4-, and ligand jexchange of [99mTc]gluconate (Sn). All complexes were characterized by high performance liquid chromatography (HPLC) on a C18 column using gradient elution with a tetrabutylammonium phosphate buffer (40-85% methanol). By performing HPLC of mixtures of the 99mTc complexes with structurally characterized 99Tc complexes of the ligands, it has been shown that at the no carrier added (NCA) level, 99mTcNCl4- labeling leads to the production of [99mTcN(dto)2]2- and [99mTcN(mnt)2]2-. Dithionite reduction and ligand exchange of 99mTc(Sn)-gluconate lead to the production of [99mTc(mnt)3]2- and not of [99mTcO(mnt)2]- which would be the expected product from the results of studies with 99Tc. The product formed by dithionite reduction in the presence of dto was not identified, but it was clearly not [TcO(dto)2]-, the product expected from 99Tc studies. Studies in mice showed that the biologic behavior of the 99mTc complexes is altered by the presence of the Tc-nitrido group. HPLC results indicate that caution must be taken when extrapolating results obtained using carrier quantities of Tc to the carrier free situation.