Constant-current potentiometric titrations of copper, lead, and cadmium at a semi-convection mercury electrode

Abstract

A semi-convection mercury electrode has been used for an indicator electrode in constant-current potentiometric titrations. Copper (II), lead (II), and cadmium (II), as low as 2×10^-5M in concentration, were titrated with disodium ethylenediamine tetraacetate solutions in an acetate buffer of pH 4.2 or 5.2.
The experimental results indicate that the titration method with the semi-convection mercury electrode has an advantage over that with the conventional dropping mercury electrode when micromolar solutions are titrated, because the former electrode has a greater sensitivity and a smaller charging current than the latter. On the other hand, the titrations with the semi-convection mercury electrode give less accurate and less reproducible results than those with the dropping mercury electrode. Nevertheless, the method was found to be useful in analyses of micromolar solution's.
It was also confirmed that the titration curves obtained at the semi-convection electrode satisfy the relation given by Tanaka et al. previously,
C=i_a-i_r/k V+v/V+cv/V,
where C represents the concentration of metal ion initially present in the solution (in mole/l), c the concentration of titrants expressed in mole/l, V the initial volume of the solution expressed in ml, v the volume (in ml) required before indicator electrode reaches the given potentials, i_a the applied current expressed in microampere, i_r the residual current in microampere at the given potentials for the observed end points, and k the sensitivity of the electrode expressed in microampere/mole/l.