Potentiometric titration of fluoride using an aluminium wire indicator electrode

Abstract

Despite the great possibilities aluminium wire electrodes are seldom used in electroanalytical techniques. Fabrication of an aluminium wire electrode is difficult and is described in detail. The proper pre-treatment for the aluminium wire electrode was found to be cathodization in sulfuric acid (1 + 3). In the plot of potential versus pF–, linearity was obtained down to 10^–6 mol l^–1 with a slope of 62 mV. Equimolar titrations of F–versus La³⁺ were carried out in aqueous solutions down to a level of 10^–6 mol l^–1 at which the curve height obtained was only 6mV at pH 2.0. All titrations were carried out in the presence of 10^–4 mol l^–1 NaClO₄. None of the other halides interfered. In 50% methanol and ethanol the titration could be carried out at 10^–9 mol l^–1 F–, pH 2.0, the curve heights obtained being 17 and 10 mV, respectively. The performance of the aluminium wire electrode was found to be far superior when compared with the performance of a fluoride ion-selective crystal membrane electrode, especially for titration. Water samples were analysed at the sub-ppm level.