Intercomparison 2135: pH, Conductivity, Alkalinity, NO3-N, Cl, SO4, Ca, Mg, Na, K, TOC, Tot-P, Al, Fe, Mn, Cd, Pb, Cu, Ni, and Zn

Abstract

Thirty-two laboratories from 17 countries accepted the invitation to join the ICP Waters chemical intercomparison and thirty of these successfully reported their 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 not as good as previous years, with an overall acceptance rate of 65% (± 20% of the “true value”, and for pH and conductivity ± 0.2 pH units and ± 10%, respectively). The lower acceptance rates can be explained by low concentrations of most of the analytes this year. The highest acceptance rates (> 80%) were obtained for some of the ions, with a maximum of 91% for sulphate. The lowest acceptance rates were for lead and total phosphorus, at 24% and 29% respectively. For lead, an error causing shipment of unpreserved metal samples to the participants may have biased the results and contributed to the low acceptance rate. 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.