Intercomparison 0115: pH, K25, HCO3, NO3+ NO2, Cl, SO4,Ca, Mg, Na, K, total aluminium, aluminium - reactive and nonlabile, TOC, COD-Mn, Fe, Mn, Cd, Pb, Cu, Ni and Zn (ICP Waters report 64/2001)

Abstract

77 laboratories received samples for the intercomparison 0115, and 72 laboratories in 26 countries submitted results. Three sample sets were used, one for the determination of major ions, one for organic matter and aluminium fractions, and one for heavy metals. Based on the general target accuracy of ± 20 %, 71 % of the results were considered acceptable. 93 % of the result pairs were acceptable for sodium and 85 % for potassium. 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. For the aluminium fractions it was decided not to evaluate the reported results, because of the great spread of the results in combination with very few results for this analytical variable in the samples C and D. Determination of heavy metals was included in the intercomparison for the second time, with fairly good results for copper and nickel. For iron, lead, and zinc the fraction of acceptable result pairs were 41 - 53 %, this low acceptance may be due to the low concentrations used for these metals. For the heavy metals it should be discussed whether an absolute acceptance limit should be used instead of the general target of ± 20 % when the concentrations are close to the detection limit of the recommended method.