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Use of High Performance Liquid Chromatography for the Structural Identification of Technetium-99m Radiopharmaceuticals at the NCA Level

Australian Radiation Laboratory, Yallambie, Australia

Correspondence: For reprints contact: J. Bonnyman, Australian Radiation Laboratory, Lower Plenty Rd., Yallambie, 3085, Australia.

ABSTRACT

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 [^99mTcN(mnt)₂]^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.