Study of Metal–Polycarboxylate Complexes Employing Ion–Selective Electrodes. Cu(II) and Cd(II) Complexes with Poly(acrylic acid) and Poly(itaconic acid)

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Abstract
The complex formation of bivalent metal ions, Cu(II) and Cd(II), with poly(acrylic acid) and poly(itaconic acid) in aqueous solutions was studied by pH titration at 25 °C and at an ionic strength of 0.1, and at the same time the concentration of free metal ions was measured using ion-selective electrodes. In order to calculate the equilibrium constants of metal–polycarboxylate complex formation, a modified Gregor method is proposed and a more reasonable method for the determination of the formation constants of the complexes is also presented. The equilibrium constant of the metal–polycarboxylate complex formation involving two carboxylate groups was calculated from this method. The value for the Cu(II)–poly(itaconic acid) complex formation was 10−2.9, and was constant in the lower neutralization region. But constant values for the Cd(II) complexes were not obtained over the entire neutralization range.