Abstract

Multicomponent aqueous systems containing Cu 2+ as metal ion, iminodiacetic acid (IDAA) as a low-molecular-weight chelating molecule, and branched poly-(ethyleneimine) (BPEI) as a polychelatogen are analyzed at different pH by UV-Vis spectroscopy and diafiltration. It was found that at pH 4, saturation of BPEI with Cu 2+ takes place at a Cu 2+:BPEI ratio of 1:5.7, probably indicating a stoichiometry for the complex of 1:4. At the same conditions the Cu 2+-IDAA complex has a stoichiometry of 1:1. The ability of BPEI to bind the metal ion is higher than that of IDAA in mixtures of both chelating molecules. Lowering the pH between 2 and 3.5, protonation of BPEI allows increasing the amounts of Cu 2+-IDAA complex so that Cu 2+ is transferred from the polychelatogen to IDAA. Good correlations are found comparing the results obtained by diafiltration and by UV-Vis spectroscopy. Moreover, diafiltration results indicate that in the absence of Cu 2+, IDAA interacts with BPEI with apparent dissociation constants of 2.88 at pH 2.7 and 0.96 at pH 4. These interactions may be responsible for the appearance of an apparent dissociation constant of 3.60 for the interactions between BPEI and the Cu 2+-IDAA complex at pH 4. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.