PRECISION OF ION-CHROMATOGRAPHIC ANALYSES COMPARED WITH THAT OF OTHER ANALYTICAL TECHNIQUES THROUGH INTERCOMPARISON EXERCISES

Three intercomparison exercises on simulated rainwater were held in 1991-1993 involving 72-98 laboratories in Europe and South America. Ion chromatography was used for the determination of anions (chloride, nitrate and sulphate) by 59-72% of the participating laboratories and for the determination of cations (Na,K, Mg and Ca) by 14-22% of them. The concentration of the single ions ranged between 5 and 150 mu mol l(-1). The results were used to evaluate the precision of the method, and showed that it was comparable to that of spectrophotometric methods. For ammonium ion, ion chromatography was used by only 4-14% of the laboratories and the results depended on the calibration technique adopted. A general improvement in precision was observed in the course of the exercises.