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IMEP-11, total cadmium, lead, arsenic, mercury and copper and extractable cadmium and lead in mineral feed
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IMEP-11, total cadmium, lead, arsenic, mercury and copper and extractable cadmium and lead in mineral feed

Report of the eleventh interlaboratory comparaison of the EU-RL-HM

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The Institute for Reference Materials and Measurements (IRMM) of the Joint Research Centre, a Directorate General of the European Commission, operates the European Union Reference Laboratory for Heavy Metals in Feed and Food (EU-RL-HM). One of its core tasks is to organize interlaboratory comparisons (ILCs) among appointed National Reference Laboratories. This report presents the results of the eleventh proficiency test (PT) of the EU-RL-HM which focused on the determination of total Cd, Pb, As, Hg and Cu and extractable Cd and Pb in mineral 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 the Certified Reference Material (CRM) BCR-032, Moroccan phosphate rock. The material was relabelled to prevent identification by the participants and was dispatched the second half of October 2010. Each participant received one bottle containing approximately 100 g of test material. Thirty-one laboratories from 26 countries registered to the exercise of which 28 reported results for total Cd and total Pb, 25 for total Hg and total Cu, 23 for total As and for extractable Cd and extractable Pb. The assigned values (Xref) for total Cd, As and Cu are the indicative values taken from the BCR-032 certificate. The assigned values (Xref) for total Pb, total Hg and for extractable Cd and Pb were provided by IRMM using isotope dilution-inductively coupled plasma-mass spectrometry (ID-ICP-MS). The Institute for Reference Materials and Measurements (IRMM) of the Joint Research Centre, a Directorate General of the European Commission, operates the European Union Reference Laboratory for Heavy Metals in Feed and Food (EU-RL-HM). One of its core tasks is to organize interlaboratory comparisons (ILCs) among appointed National Reference Laboratories. This report presents the results of the eleventh proficiency test (PT) of the EU-RL-HM which focused on the determination of total Cd, Pb, As, Hg and Cu and extractable Cd and Pb in mineral 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 the Certified Reference Material (CRM) BCR-032, Moroccan phosphate rock. The material was relabelled to prevent identification by the participants and was dispatched the second half of October 2010. Each participant received one bottle containing approximately 100 g of test material. Thirty-one laboratories from 26 countries registered to the exercise of which 28 reported results for total Cd and total Pb, 25 for total Hg and total Cu, 23 for total As and for extractable Cd and extractable Pb. The assigned values (Xref) for total Cd, As and Cu are the indicative values taken from the BCR-032 certificate. The assigned values (Xref) for total Pb, total Hg and for extractable Cd and Pb were provided by IRMM using isotope dilution-inductively coupled plasma-mass spectrometry (ID-ICP-MS). For total Cd, As, Hg and Cu and for extractable Cd, the uncertainty of the assigned values (uref) was calculated by combining the uncertainty of the characterization (uchar) and a contribution for between-bottle homogeneity (ubb) (which was calculated from the certification report). For total and extractable Pb the number of replicates performed to establish the assigned value was higher (11 replicates) than for the other measurands (6 replicates). Since the aliquots were taken from different bottles, it was assumed that uchar included a contribution for the homogeneity. For total Cd, As and Cu, uchar were taken from the CRM certificate as indicated by the producer. For extractable Cd the same uchar as for total Cd was used. For total Pb and Hg and for extractable Pb, uchar was calculated according to the ISO Guide for the Expression of Uncertainty in Measurement (GUM). Participants were invited to report the uncertainties of their measurements. This was done by the majority of the laboratories taking part in this exercise. Laboratory results were rated using z- and _-scores (zeta-scores) in accordance with ISO 13528. The standard deviation for proficiency assessment ( σˆ), also called target standard deviation, were calculated applying the modified Horwitz equation for total Cd, As and Cu and for extractable Cd. However, for total Hg, σˆ was set to 15 % on the basis of previous experience of the EU-RL-HM with this network of laboratories. For total Pb, σˆ was set at 25 % due to micro-inhomogeneity observed when small aliquots were taken for analysis. For extractable Pb we used the same criteria as for total Pb to score the participants ( σˆ= 25 %). Between 70 and 80 % of the laboratories reported satisfactory results for all measurands but Hg. For the latter, only 57 % of the laboratories submitted satisfactory results. All the questionable and unsatisfactory results for Hg were obtained using direct thermal decomposition-based methods.
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ISSN 1018-5593
ISBN 978-92-79-19713-0
DOI 10.2787/39676
Número de catálogo LA-NA-24758-EN-C
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ISSN 1018-5593 ISBN 978-92-79-19713-0 DOI 10.2787/39676 Número de catálogo LA-NA-24758-EN-C
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