Determination of chloride in high-purity waters in the range 0–20 µg l–1 of chloride using ion-selective membrane electrodes incorporating mercury(I) chloride

Two types of solid-state mercury(I) chloride electrodes have been used to determine chloride in the concentration range 0–20 µg l–1. At these low concentrations, more chloride will dissolve from the mercury(I) chloride in the electrode than is present in the sample itself. The extent of the dissolution is controlled, however, by the chloride in the sample. In these circumstances, the electrode potential is linearly related to the concentration of chloride in the sample. With the electrode housed in a flow cell with a thermostatically controlled water jacket, the correlation coefficient between e.m.f. and concentration was always greater than 0.99. The sensitivity (0.18 mV per µg 1–1 of chloride at 25 °C and 0.4–0.5 mV per µg l–1 of chloride at 4 °C) was about ten times greater than that of the silver-silver chloride electrode. Total standard deviations at 10, 5 and 2 µg l–1 of chloride were 0.4, 0.5 and 0.3 µg l–1 of chloride, respectively.