Reference electrodes for use in the potentiometric determination of chloride. Part II. Quinhydrone electrodes

Abstract

Reference electrodes consisting of platinum or gold electrodes immersed in solutions of constant pH saturated with quinhydrone have been tested for use in potentiometric analysis for chloride. The solution inside the reference electrode is matched in composition with the main components of the treated sample solution (i.e., after addition of reagents to control pH and ionic strength but excluding the determinand). In this way the effect of the liquid-junction potential is minimised. The electrodes have a sealed construction and need no maintenance.

The potentials of newly made electrodes change at a greater rate than those of the mercury-mercury(I) sulphate reference electrodes normally used in chloride analysis, but after 3–4 weeks the rate of change of potential is similar to that obtained from the best commercial mercury-mercury(I) sulphate electrodes. Older electrodes develop anomalous temperature responses.

The quinhydrone reference electrode is comparable to the best mercury-mercury(I) sulphate electrodes in media used with mercury(I) chloride sensing electrodes (typically 0.01 mol l^–1 nitric acid). In the media of higher pH used with silver chloride sensing electrodes (typically pH 4.3–5.0 acetic acid-ammonium acetate buffer solution), the performance of the mercury-mercury(I) sulphate electrode is improved, while that of the quinhydrone electrode deteriorates; the former would, therefore, generally be preferred.

This work has provided the basis for similar but improved electrodes, using more chemically stable constituents, which will be described in Part III.