Certification of the lead mass fraction in wine for comparison 16 of the International Measurement Evaluation Programme

Comparison 16 of the International Measurement Evaluation Programme (IMEP) focused on the evaluation of measurement performance for the determination or the Ph mass fraction in a commercial red wine, resulting in a demonstrat ed degree of equivalence for laboratories internationally. IMEP-16 wine tes t samples were tested for homogeneity and stability to pressure and tempera ture variations (isochronous comparison). Pb concentration in the average t est sample was certified using the combination of a straightforward microwa ve sample digestion protocol and inductively coupled plasma isotope dilutio n quadrupole mass spectrometry applied as a primary method of measurement. Certification of SI traceable reference values was achieved to 1.2% relativ e expanded uncertainty (k = 2). Nearly half of the uncertainty was due to t he measured sample homogeneity correction factor (1 +/- 0.4%), followed by the contributions from the corrections for instrumental background and the dead time effects (respectively about 5%, and 23% of the calculated combine d uncertainty), and the contribution from the measurements performed to cor rect for mass discrimination effects (12.3% in total). 129 laboratories fro m 33 countries participated in IMEP-16. The results are spread over a broad range of values (from <1 to >2900 mug L-1), and one third ties below -50% or above +50% deviation from the certified Pb concentration. About 40% of a ll participants reported accurate results to within +/- 10% uncertainty. Fo r the vast majority, measurement uncertainty was largely underestimated. Th e quality of results does not seem to be correlated either to the self-decl ared experience in this type of measurements, or to the type of analytical technique applied. Identical samples were distributed to 14 National Measur ement Institutes (from 12 countries and the IRMM) within the frame or the C CQM-P12 pilot study. All their results were in agreement within +/- 10% of the IMEP-16 certified value, thus offering a striking contrast with the spr ead of IMEP-16 results.