ON THE COMPLEXATION OF CD(II) IONS WITH POLYACRYLIC-ACID

Complexation of Cd(II) ions with polyacrylic acid has been studied pot entiometrically and by Cd-113 NMR spectroscopy. A Donnan model propose d by Marinsky (Marinsky, J. A., in ''Ion Exchange and Solvent Extracti on'' (J. A. Marinsky and Y. Marcus, Eds.), Vol. 11, p. 237. Dekker, Ne w York, 1993; Miyajima, T., in ''Ion Exchange and Solvent Extraction'' (J. A. Marinsky and Y. Marcus, Eds.), Vol. 12, p. 275. Dekker, New Yo rk, 1995) has been applied in order to correct for the electrostatic e ffect on the equilibria inherent in the polyelectrolyte nature of the polyions. The potentiometric studies showed that the bidentate ligand complex, (CdA(2))(0), is the dominant species, but the formation of mo nodentate ligand complex, (CdA)(+), cannot be neglected at low degree of dissociation of the polyacid. The stability constants of the (CdA)( +) and (CdA(2))(0) complexes have been determined to be approximately 3.2 X 10 and 1.6 X 10(2), respectively. These values are in good agree ment with the stability constants of 4.1 X 10 and 1.0 X 10(2) for Cd(a cetate) and Cd(glutarate) complexes, where acetate and glutarate ions are the monomer analog ligands of polyacrylic acid. The Cd-113 NMR che mical shift change upon dissociation of the polyacid also indicates th at the dominant complex is (CdA(2))(0), but (CdA)(+) becomes more appr eciable with the decreasing degree of dissociation of the polyacid. (C ) 1996 Academic Press, Inc.