Chemical Intercomparison 2539: pH, conductivity, alkalinity, colour, NO3-N, NH4-N, Cl, SO4, Ca, Mg, Na, K, phosphate, silica, TOC, Total-P, Total-N, Al, Fe, Mn, Cd, Pb, Cu, Ni, and Zn

Summary

Thirty-one laboratories from fifteen countries accepted the invitation to join the ICP Waters chemical intercomparison. Three sets of samples were prepared and distributed to the participants: one for the determination of ions, one for metals, and one final set of synthetic samples for determination of nutrients. The synthetic sample set was new for 2025 and led to better performance and better assessment of results. Also new for 2025 was the inclusion of colour, ammonium, phosphate and silica. Acceptance rates were based on the Z’-scores obtained by the participants. General trends in the choice of techniques continue to shift towards plasma from atomic absorption, and to mass detection from ionic emission. This is promising especially for the determination of metals at low levels.