Solid-state mercury(I) chloride electrode for determining 0.1–1.0 µg ml–1 levels of chloride in boiler water and other high-purity waters

A solid-state electrode based on mercury(I) chloride and mercury(II) sulphide has been developed for determining chloride concentrations of 0.01–1.0 µg l–1 in boiler water. The greater sensitivity of the electrode compared with that of silver-silver chloride electrodes enables concentrations as low as 0.01 µg ml–1 to be determined by a simple manual technique. The total standard deviations at chloride concentrations of 0.5, 0.1 and 0.01 µg ml–1 were 0.025, 0.005 and 0.015 µg ml–1, respectively. The electrode can be prepared easily in the laboratory from commercially available materials and a Růžička Selectrode. The only significant interference is from iron(III) ions and this interference can be eliminated by adding fluoride ions to the sample.