MIXED POTENTIAL RESPONSE AT METALLIC ELECTRODES IN POTENTIOMETRIC DETECTION FOR ION CHROMATOGRAPHY

The response characteristics of metallic copper and silver-silver chloride electrodes in a single potentiometric detector were evaluated in an ion chromatographic system. A cell design was used in which the position of the electrodes can be moved easily. Response to inorganic anions was found to be possible with either the copper or the silver-silver chloride electrode acting as the indicator electrode in the same cell where a change in function is achieved by simple movement of the electrodes in the cell. Either negative or positive peaks may be observed in direct or indirect detection modes depending on the choice of mobile phase composition and on the electrode positions in the detector. Optimum separations and the best potentiometric response were achieved with 1 mM sodium perchlorate as the eluent. The response to chloride and bromide is shown to be more sensitive at the silver electrode and to nitrate, nitrite, iodide, thiosulphate and thiocyanate at the copper electrode. The best detection limit was found to be 10 pmol for bromide at the silver-silver chloride electrode.