Analysis of Complexation Equilibria of Polyacrylic Acid by a Donnan-Based Concept

Abstract Complexation equilibria of uni- and divalent metal ions (Ag + , Ca 2+ , Cu 2+ , and Pb 2+ ) with polyacrylic acid (PAA) have been studied at various degrees of dissociation (α) of PAA under different sodium salt concentration levels at 25°C. Both pH and p M ( M Z+ = Ag + , Ca 2+ , Cu 2+ , and Pb 2+ ) of equilibrium mixture solutions of M Z+ /PAA/Na + (excess) have been determined concurrently by a potentiometric titration method. The electrostatic effect inherent in the polyion–metal ion binding equilibria has been evaluated by a Donnan-based concept and is corrected for by the use of a nonideality term of acid dissociation equilibria of the polyacid as a probe. For Ag + –PAA and Ca 2+ –PAA bindings, only monodentate ligand complexes, (MA) ( Z −1) , have proven to be formed, whereas for Cu 2+ and Pb 2+ ion bindings, formation of both monodentate and bidentate ligand complexes have been observed. For both Cu 2+ –PAA and Pb 2+ –PAA systems, bidentate carboxylate complex formation is predominant at α > ca. 0.3, whereas at α