Oxidation states of 99mTc in technetium chelates studied by the ICES method

Abstract

The chemical shifts of 99mTc core-electron binding energies were measured in solid samples by means of the internal conversion electron spectroscopy (ICES) method. Technetium chelates with citric acid, DTPA, EDTA and ethylenediamine- N, N′-tetraacetohydroxamic acid (EDTAHA) as ligands were prepared in solution at (2–4) × 10 −7 M Tc concentration (no-carrier-added). The samples for ICES measurements were made by evaporation of the solution in vacuum to dryness. The following chemical shifts ΔE B [K 99mTcO 4- 99mTc(chelate)] were found in the systems investigated: 1.9 and 4.1 eV for 99mTc(Sn)citr; 2.1, 3.2 and 4.3 eV for 99mTc(Sn)DTPA; 1.9 and 3.6 eV for 99mTc(Sn)EDTA; 1.8 and 3.3 eV for 99mTc(Sn)EDTAHA. Standard deviations of the shifts are 0.2 eV. These shifts were compared with those of inorganic technetium oxocompounds and correlated with oxidation states via a potential model. It was concluded, that these shifts refer to technetium oxidation states in chelates as follows: 1.8–2.1 eV to 99mTc(V), 3.2–3.6 eV to 99mTc(IV) and 4.1–4.3 eV to 99mTc(III).