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Abstract
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 various types of inter-laboratory comparisons in support of European Union policies. This paper presents the results of a proficiency testing exercise (PT) focusing on the determination of total cadmium (Cd) and total lead (Pb) mass fractions in baby food in support to Commission Regulation (EC) 1881/2006 of 19 December 2006 setting maximum levels for certain contaminants in foodstuffs. The test material used in this exercise was soya-based baby food formula purchased in a local pharmacy and prepared by the Reference Materials Unit of the IRMM for this exercise. Sixty-six laboratories from 23 countries registered to the exercise and 61 of them reported results. Each participant received one bottle containing approximately 15 g of test material. Participants were asked to quantify the measurands in the powder and in the reconstituted formula. Reference values independent from the participants’ results were established using isotope dilution inductively coupled plasma mass spectrometry. The total Cd mass fraction was determined by IRMM and LGC Ltd (UK), while the total Pb was determined by IRMM. The standard deviation for proficiency assessment was set at 22% of the assigned value for all measurands. Laboratories were rated with z- and ζ- (zeta) scores in accordance with ISO 13528. The outcome of this exercise is clearly influenced by the very low level of Cd and Pb content in the test material which triggered: a high number of ‘less than’ values; overestimated values especially for Pb very likely due to contamination; and a visible method influence in the case of Pb (methods based on atomic absorption were not sensitive enough to attain such low limits of detection). The results were also evaluated with regard to the reported limit of detection and some incoherencies were observed.
Acknowledgements
C. Contreras and P. Connely from the Reference Materials Unit of IRMM are acknowledged for their support for setting-up the short-term stability study of the test material and for checking the drying method against Karl-Fisher titration. J. Charoud-Got is acknowledged for the processing of test materials. B. Ari (IRMM and now TUBITAK-UME) is acknowledged for her early investigations on a similar type of test material that helped on the decision on a strategy for the choice and preparation of the IMEP-33 test material. D.Malinovskiy, S. Hill, S. Merson, L. Evans and H. Goenaga (LGC Ltd) are acknowledged for contributing to the certified value for total cadmium. Franz Ulberth and I. Fiamegkos (IRMM) are thanked for revising the manuscript. I. Verbist and B. Kortsen (IRMM) are acknowledged for their logistic support. Laboratories that participate in this exercise are also acknowledged.