PROTOLYTIC CONTROL IN STRIPPING VOLTAMMETRIC TITRATIONS OF METAL POLYACID COMPLEXES

A systematic study was made of the influence of variations of pH and of other protolytic parameters on the voltammetric response of metal-polyacid systems. The complexation of metal ions at the 10(-6) mol l-1 concentration level was measured by different procedures, including control of pH and of the degree of dissociation (alpha(d)) of the polyacid. The results show that, in order to obtain realistic values of the formation constant of the metal-polyacid complexes, voltammetric titrations must be done under conditions of constant-alpha(d). A procedure involving the adjustment of the pH of the metal solution to the same value as that of the polyacid solution was found to yield a practically useful method for maintaining constant complexation conditions (constant-alpha(d)). Experimental evidence was obtained by means of differential-pulse anodic stripping voltammetry for the model system Zn(II)-polymethacrylic acid.