Differential electrolytic potentiometry with periodic polarisation. Part XXII. Symmetrical periodic current differential electrolytic potentiometry in oxidation-reduction titrimetry

Abstract

The application of pure, symmetrical, bias-free square, sine and triangular wave periodic polarisation to all types of oxidation-reduction titrations is reported. Electrode configuration and earthing and the destructive effective of bias are examined. Titration curve shapes are the same as those of classical d.c. differential electrolytic potentiometry, but the periodic current densities required are much higher than for d.c. The electrode response speed is greatly accelerated, unpoised potentials are steady, warning is given of the approach of the end-point in type II (b) titrations, electrodes retain full activity for very long periods and errors in titrations of iron(II) with dichromate or cerium(IV) are eliminated in the periodic method as against the d.c. method. Discrimination in type II reactions is slightly attenuated in the periodic method, and in titrations at low concentrations it is considerably attenuated. The nature and the conditions of the titration, the speed of the electrode charge-transfer process, the ballast load, the current density, the electrode area, the shape of the applied waveform, the applied frequency, and the deactivation of electrodes, are examined in detail. The benefit of the constant-current mode over the constant-potential mode is demonstrated.