Interlaboratory exercises to compare analytical method performances

Three intercomparison exercises on simulated rainwater were held in the period 1991-93 involving 72 to 99 laboratories in Europe and South America. The exercises required the analysis of pH, conductivity, main anions (Cl-, NO3- and SO42-) and main cations (Ca2+, K+, Mg2+, Na+ and NH4+). The concentrations of the single ions ranged between 5 and 150 mu mol l(-1). Results were used to evaluate and compare the precision of the analytical methods. A general improvement in precision was observed in the course of the exercises.