Report of the Third Interlaboratory Comparison Organised by the Community Reference Laboratory for Heavy Metals in Feed and Food - Total Cd, Pb and Hg and Extractable Cd and Pb in Feed

The Institute for Reference Materials and Measurements (IRMM) of the European Commission's Directorate-General Joint Research Centre holds the Community Reference Laboratory for Heavy Metals in Feed and Food (CRL-HM). One of its core tasks is to organise interlaboratory comparisons (ILCs) among appointed National Reference Laboratories (NRLs). This report presents the results of the third ILC of the CRL-HM which focused on the determination of total Cd, Pb and Hg and extractable Cd and Pb in feed according to Directive 2002/32/EC of the European Parliament and of the Council on undesirable substances in animal feed. The test material used in this exercise was a commercial compound feed for fish provided by the Centro di Referenza Nazionale per la Sorveglianza e il Controllo degli Alimenti per Animali, Istituto Zooprofilattico del Piemonte. The material, naturally contaminated, was processed, bottled, labelled and dispatched by the Reference Materials Unit of the IRMM. The samples were dispatched on the second half of October 2007. Each participant received one bottle containing approximately 20 g of test material. Thirty-one participants from 25 countries registered to the exercise of which 31 submitted results for total Cd and total Pb, 28 for total Hg, 26 for extractable Cd and 24 for extractable Pb. The assigned values (Xref) were provided by IRMM using isotope dilution-inductively coupled plasma-mass spectrometry (ID-ICP-MS). The analytical uncertainty of Xref, uchar, was calculated according to the ISO Guide to the Expression of Uncertainty in Measurement (GUM)2. Homogeneity and stability studies were subcontracted to Bundesanstalt für Materialforschung und ¿Prüfung (BAM). The uncertainties of the respective assigned values, uref, were calculated combining the analytical uncertainty, uchar, with a contribution for the between-bottle homogeneity, ubb, and for the short term stability of the test material, usts. Participants were invited to report the uncertainty on their measurements. This was done by 29 laboratories for total Cd, 23 for total Pb, 25 for total Hg, 18 for extractable Cd and 13 for extractable Pb. Laboratory results were rated with z and zeta scores in accordance with ISO 135283. Standard deviation for proficiency assessment (also called target standard deviation) were calculated using the modified Horwitz equation and were 22 % of the assigned value for total Pb and Hg and for extractable Pb and 16 % of the assigned value for total and extractable Cd.JRC.D.4-Isotope measurement