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^–, NO ₃ ^– and SO ₄ ^2– ) and main cations (Ca²⁺, K⁺, Mg²⁺, Na⁺ and NH ₄ ⁺ ). The concentrations of the single ions ranged between 5 and 150 moll^–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.