IMEP-28, total arsenic, cadmium, lead and mercury in food supplements : 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 in food supplements relying on Commission Regulations 333/2007 and 1881/2006. The test material used in this exercise was the candidate standard reference material (SRM) SRM 3256, of the National Institute of Standards and Technology (NIST), the matrix being green tea food supplement. The material was labeled at IRMM and dispatched to the participants on the first week of June 2009. Each participant received two sachets containing approximately 2.5 g of test material each. Sixty-two participants from twenty countries registered to the exercise of which 46 reported results for total Cd, 50 for total Pb, 42 for total As and 40 for total Hg. The assigned values were the reference values as provided by NIST. The uncertainties, Uref, of the respective assigned values were also provided by NIST. Participants were invited to report the uncertainty on their measurements. This was done by 49 of the 58 laboratories having submitted results in this exercise. Laboratory results were rated with z and zeta scores in accordance with ISO 13528. Standard deviation for proficiency assessment (also called target standard deviation) was fixed to 15 % for total Cd, Pb and As by the advisory board of this ILC, on the basis of the outcome of previous ILC's, and 22% for mercury based on the modified Horwitz equation. The outcome of the exercise was altogether positive, with over 60 % of the participants reaching satisfactory scores for both types of scorings for almost all elements.