Intercomparison 2034: pH, Conductivity, Alkalinity, NO3-N, Cl, SO4, Ca, Mg, Na, K, TOC, Tot-P, Al, Fe, Mn, Cd, Pb, Cu, Ni, and Zn

Abstract

Twenty-one laboratories from 13 countries accepted the invitation to join the ICP Waters chemical intercomparison and successfully reported results. The lower number of participants this year likely resulted from the global covid-19 pandemic, leading to the lockdown of several nations during the spring of 2020. Two sets of samples were prepared and successfully distributed to the participants: one for the determination of ions and one for the metals. In general, the results were good with an overall acceptance of 81% (± 20% of the “true value”, and for pH and conductivity ± 0.2 pH units and ± 10%, respectively). The highest acceptances (> 90%) were obtained for some of the ions and metals, with a maximum of 100% for sodium. This year, the acceptance for pH was also very good (75%). The lowest acceptance rate was for total phosphorus 41% of the results being accepted. This number was originally reported as 18% due to an error with the units. A relatively low acceptance was also achieved for alkalinity which likely resulted from the large number of different titration methods used by the participating laboratories. General trends in the choice of techniques continue to shift towards plasma from atomic absorption, and to mass detection from ionic emission. This is especially promising for the determination of metals at low levels.