INFLUENCE OF THE COUNTERION CONCENTRATION ON THE FORMATION-CONSTANTS OF SOME METAL POLYCARBOXYLATE COMPLEXES - STUDY BY DIFFERENTIAL PULSE ANODIC-STRIPPING VOLTAMMETRY

The influence of counterion concentration on the complex formation of Zn(II), Cd(II) and Pb(II) with polymethacrylic acid (PMA) and polyacrylic acid (PAA) is studied by differential pulse anodic stripping voltammetry (DPASV). Titrations of Zn(II) or Cd(II) or Pb(II) with partially neutralized PMA or PAA at different KNO3 concentrations (C(K)) allows the precise determination of the apparent formation constant (K) of the systems, through analysis of cur-rent data alone and both current and potential data obtained by DPASV. Linear relationship between log K and log C(K), with slope values within the range - 1.7 to - 2.2, are obtained. The possible causes of some anomalous behaviours observed for PAA systems with respect to the voltammetric model assumed are discussed.