DIRECT-CURRENT, NORMAL-PULSE AND REVERSE-PULSE POLAROGRAPHY OF SOME HEAVY-METAL POLYCARBOXYLATE COMPLEXES

Complex formation of Zn(II) and Cd(II) with polymethacrylic acid (PMA) andpolyacrylic acid (PAA) is studied by sampled direct-current, normal-pulse and reverse-pulse polarography. The combined use of these techniques serves a twofold purpose: to cover different time windows and to eliminate interferences from adsorption of the metal ion induced by the ligands. The two Zn(II) systems appear to be labile on the different time scales. The association constants (K) evaluated from potential data and those from current data show good consistency. The dependence of K on the degree of neutralization (αn) is much stronger for PAA complexes than it is for those of PMA. With the Cd(II)-PMA system complications from induced Cd(II) adsorption are completely removed by using reverse-pulse polarography. The system is not liable and stabilities derived from potential data differ from those obtained from current data. The remaining discrepancy cannot be attributed to simple association and dissociation kinetics. © 1990.