ABSTRACT
The interaction of La [III] with some selected antibiotics e.g. ampicillin, cephalexin, cephradine, oxytetracycline and tetracycline were studied by potentiometric or pH titrations. The stability constants of different binary complexes formed in such system have been determined at 25 +/- 0.1 and an ionic strength [M] of 0.1 mol. 1-1 by using the computer program Miniquad. The results showed the formation of 1: 1 complexes together with the corresponding hydrolyzed species. The solid complexes were separated and their composition and structure were confirmed by elemental analysis, IR spectrometry and conductometric measurements. The results showed that the beta-lactam antibiotics act as bidentate ligands, coordinated to the La [III] through the amino and the carbonyl-groups of side chain