Intercomparison 1832: pH, Conductivity, Alkalinity, NO3-N, Cl, SO4, Ca, Mg, Na, K, TOC, Tot-P, Al, Fe, Mn, Cd, Pb, Cu, Ni, and Zn

Summary

In the current edition, 32 laboratories from 19 countries were included in the 2019 ICP-Waters intercomparison. Similar to earlier intercomparisons, two sample sets were prepared: one for the determination of major ions and one for heavy metals. Based on the general target accuracy of  20%, or the special accuracy limit for pH and conductivity ( 0.2 pH units and  10% respectively), 81% of the overall results were accepted. The best results were for the variables sulphate, calcium, iron, manganese, and zinc. For these variables the acceptance was higher than 90%. Good results were obtained this year also for pH, in contrast to with previous editions. 81% of the participants provided results within the acceptance criteria. The higher accuracy in the pH results in this year was due to the ease of its determination when compared earlier; instead of circumneutral or slightly acidic pH, the sample set AB had been adjusted to acidic pH; about 4.5. The analysis of Total-P has exhibited a remarkable increase in the quality of the results; 33% of the results provided by the participants met the acceptance criteria (in contrast with the 21% obtained in the former edition). Harmonization of the analytical methods used may be the most important way to improve the comparability for these parameters.