Report of the fifth Interlaboratory Comparison organised by the Community Reference Laboratory for Heavy Metals in Feed and Food Total Cd, Pb and As as extractable Cd and Pb in Mineral Feed

Abstract

The Institute for Reference Materials and Measurements (IRMM) of the Joint Research Centre, a Directorate-General of the European Commission, operates 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 fifth ILC of the CRL-HM which focused on the determination of total Cd, Pb and As and extractable Cd and Pb in mineral feed according to Directive 2002/32/EC1 of the European Parliament and of the Council on undesirable substances in animal feed. The test material used in this exercise was a commercial mineral feed for piglets provided by AGES, Zentrum Analytik und Mikrobiologie, in Austria. 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 2008. Each participant received one bottle containing approximately 30 g of test material. Thirty-one participants from 25 countries registered to the exercise of which 29 submitted results for total Cd and for total Pb, 22 submitted results for total As and 27 submitted results for extractable Cd and for extractable Pb. Two laboratories did not submit results due to a break down in the instruments that were to be used for the analyses. The assigned values (Xref) for total and extractable Cd and Pb 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. The assigned value for total arsenic was provided by the Studiecentrum voor Kernenergie (SCK-CEN) using neutron activation analysis. The analytical uncertainty of Xref, uchar, for total arsenic was calculated according to GUM3,4. Homogeneity and stability studies were subcontracted to Bayer Antwerpen. 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 of their measurements. This was done by 25 laboratories for total Cd, 24 laboratories for total Pb, 18 laboratories for total As, 22 laboratories for extractable Cd and 21 laboratories for extractable Pb. The laboratory performance was evaluated using z and zeta scores in accordance with ISO 135285. The standard deviations for proficiency assessment (also called target standard deviation) were calculated using the modified Horwitz equation6 and were between 15 and 16 % for all the measurands .