Intercomparison 0216: pH, K25, HCO3, NO3+ NO2, Cl, SO4, Ca, Mg, Na, K, Fe, Mn, Cd, Pb, Cu,Ni and Zn (ICP Waters report 68/2002)

Abstract

79 laboratories received samples for the intercomparison 0216, and 75 laboratories in 27 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 %, 68 % of the results were considered acceptable. The best results were reported for the analytical variables sodium, sulfate and manganese, where 88, 76 and 76 % of the results were acceptable. The worst results were observed for alkalinity, nitrate + nitrite, and lead, common for these analytical variables is that the concentrations are rather low. For pH only 58 % of the result pairs were acceptable in relation to the extended target accuracy of ± 0.2 units. Normalization of the analytical methods used is necessary to improve the comparability for pH. Determination of heavy metals was included in the intercomparison for the third time, with fairly good results for most of them. The lowest acceptance was obtained for lead, 59 %, and this may be due to the low concentrations used for the metal.