Mixed ligand derivatives of 1:1-Th(IV)-DTPA chelate with lactic, mandelic and o-hydroxynaphthoic acids

Potentiometric studies of the mixed ligand derivatives of 1:1-Th(IV)-DTPA chelate (where DTPA=diethylenetriamine pentaacetic acid) with certain secondary ligands, such as lactic, mandelic and o-hydroxynaphthoic acids have been carried out. The pH-titrations of the reaction mixtures containing 1:1:1 molar ratio of metal ion to DTPA to secondary ligand have shown the formation of 1:1:1 ternary complexes at higher pH (approximately 8). The equilibrium constants of the resulting mixed complexes have been determined at 30+-10C and μ=0.1 (KNO3) and the order of stability in terms of secondary ligands has been found to be o-hydroxy napthoic acids>mandelic acid>lactic acid. (author)