Intercomparison 0721: pH, Cond, HCO3, NO3-N, C1, SO4, Ca, Mg, Na, K, Fe, Mn, Cd, Pb, Cu, Ni, and Zn (ICP Waters report 90/2007)

Abstract

75 laboratories received samples for the intercomparison 0721, and 72 laboratories in 28 countries submitted results. Two sample sets were used, one for the determination of major ions, and one for heavy metals. Based on the general target accuracy of 20 %, 73 % of the overall results were considered as acceptable. The best results were reported for the analytical variables sodium and calcium, with 92 and 86 % acceptable results, respectively. Low percentage of acceptable results was observed for some heavy metals, especially zinc with 53 % acceptable results. The main reason is the low concentrations of the metals in the samples used. This time the worst case was pH with only 51 % of the results being acceptable. Harmonization of the analytical methods used and the practical procedures followed is probably most important to improve the comparability for pH.