IMEP-30 : total arsenic, cadmium, lead and mercury, as well as methylmercury and inorganic arsenic in seafood : interlaboratory comparison report

The Institute for Reference Materials and Measurements (IRMM) of the Joint Research Centre (JRC), a Directorate-General of the European Commission, operates the International Measurement Evaluation Programme IMEP. It organises interlaboratory comparisons (ILC's) in support to EU policies. This report presents the results of an ILC which focussed on the determination of total As, Cd, Pb, and Hg, as well as methylmercury and inorganic arsenic in seafood. The test material used in this exercise was the Certified Reference Material (CRM) DOLT-4, dogfish liver of the National Research Council of Canada (NRC). The material was relabelled and was dispatched end of May 2010. Each participant received one bottle containing approximately 20 g of test material. Fifty-seven laboratories from 29 countries registered to the exercise and all of them reported results. The assigned values and their associated uncertainties for total As, Cd, Pb, Hg and methylmercury are the certified values taken from the DOLT-4 certificate. An attempt was made to establish an assigned value for inorganic As (iAs) using the results provided by a group of five laboratories expert in the field, following a similar approach to that used in IMEP-107 [1], a ILC on total and inorganic arsenic in rice. Unfortunately, contrary to what was observed in IMEP-107, the results obtained by the expert laboratories for iAs showed a large spread reason and no assigned value could be established. Participants were invited to report the uncertainty of their measurements. This was done by the majority of the laboratories taking part in this exercise. Laboratory results were rated with z- and ζ-scores (zeta-scores) in accordance with ISO 13528 [2]. No scoring was provided to laboratories for submitted results of iAs. The standard deviation for proficiency assessment (also called target standard deviation) was fixed to 15 % by the advisory board of this ILC, on the basis of the outcome of previous ILCs organised by IMEP and on the state-ofthe- art in this field of analysis. The outcome of the exercise was in general positive, the share of satisfactory z-scores ranging between 80 and 96 %. Results for total As, and to a lesser extent for total Cd, showed a tendency for underestimation. As for iAs, the same spread of result than for the certifiers could be observed with the participants' results. No method influence could be detected, but the matrix seems to have a major impact.