Ion chromatography of inorganic anions with potentiometric detection using a metallic copper electrode

Abstract

The determination of inorganic anions by ion chromatography with potentiometric detection using a metallic copper indicator electrode is described. The electrode response to inorganic anions can result from consumption of cuprous and cupric ions in the diffusion layer at the electrode surface, from production of copper ions due to oxidation of metallic copper, or as a result of displacement of a copper-complexing ligand from the eluent by an eluted non-complexing inorganic anion. The first possibility is exemplified by the determination of cyanide, chloride, bromide, iodide and thiocyanate, whereas the second possibility is illustrated by the determination of iodate, bromate and chlorate. An example of the indirect detection method is the determination of nitrite, nitrate and sulphate, using sodium tartrate as eluent. Calibration data for all of the above detection methods are provided and are interpreted in terms of theoretical response equations. Detection limits are also presented and are shown to be strongly dependent on the chromatographic conditions used and on the electrode response mechanism applicable to each anion.