International measurement evaluation programme: IMEP-9, trace elements in water

The International Measurement Evaluation Programme (IMEP) is an interlabora tory comparison scheme, founded, owned and coordinated by the Institute for Reference Materials and Measurements (IRMM) since 1988. IMEP-9 is the thir d round of trace elements in water evaluation following IMEP-3 and IMEP-6. Reference values for 15 elements stating total concentrations and combined uncertainties (according to GUM) were established. The reference values wer e established mainly by isotope dilution mass spectrometry (IDMS) as a prim ary method of measurement, and values traceable to the SI were obtained. Th e four elements that could not be certified by IDMS were assigned values by means of other measurement techniques. Results from 201 laboratories from 35 countries and four continents were evaluated against the reference value s and the comparability between the laboratories is presented graphically.