Intercomparison 1933: pH, Conductivity, Alkalinity, NO3-N, Cl, SO4, Ca, Mg, Na, K, TOC, Tot-P, Al, Fe, Mn, Cd, Pb, Cu, Ni, and Zn

Abstract

A total of 36 laboratories from 19 different countries accepted the invitation to join the ICP-Waters chemical intercomparison, and 33 laboratories from 16 different countries successfully reported results. 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 75% ( 20% of the “true value”, and for pH and conductivity  0.2 pH units and  10%, respectively). The highest acceptance ratios were found for the ions: sodium, chlorine, calcium, and magnesium, all being higher than 90%. The lowest acceptance ratio was found for total phosphorus with only 35% of the results being accepted. However, the concentration of total phosphorus was relatively low, and this parameter was only recently introduced into the test. For several of the parameters a relatively high number of different techniques had been used, which can lead to systematic errors in the results. This was investigated for pH and alkalinity, but no clear connections could be found between the systematic error in the results and the techniques employed. 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.