Amperometric ion-selective electrode. Voltammetric theory and analytical applications at high concentration and trace levels

The theory of normal pulse voltammetry (NPV) and cyclic potential sweep voltammetry (CV) of the amperometric ion-selective electrodes (AISEs) based on the ionophore-assisted transfer of ions across polarized organic solvent or oil ∣ water (O ∣ W) interfaces is discussed. The numerical solution of the resulting integral equations has been used to show how their voltammograms vary with the ratio of the concentration of analyte ion in the W phase, that is, the test solution, to that of ionophore in the O phase, that is, the ion-sensitive membrane. Generally, the current response of the AISEs at constant ionophore concentration is not linear with respect to the concentration of analyte ion when the ratio exceeds 0.01. In order to obtain a linear calibration curve in a wide range of analyte concentrations, up to a few molar of Na + ion, e.g. a new technique, called F-pulse amperometry, is proposed and experimentally verified, where a pulse voltage corresponding to the ‘foot-of-wave’ potential is applied and the current is sampled according to the NPV technique. When the concentration of analyte ion is very low, the stripping voltammetry technique is promising. Poly(oxyethylene)alkyl ether surfactants at ppb levels can be determined using the stripping voltammetry technique based on the electrochemical pre-concentration of the surfactants by ion-assisted transfer at the O-gel ∣ W interface.