Preparation of an infant formula proficiency testing material and assessment of its homogeneity and stability

Abstract

The European Union Reference Laboratory for Chemical Elements in Food of Animal Origin (EURL-CEFAO) is a proficiency testing (PT) provider accredited according to ISO Guide 43-1 and later to ISO/IEC 17043:2010. It organizes exercises devoted to expert laboratories of the EU Member States. PTs are proposed taking into account matrices, analytes, maximum levels (MLs) ruled in Commission Regulation (EC) 1881/2006 (and following amendments) and discussions about new or modified MLs. Following this approach, an exercise was organized in 2012 on the measurement of the cadmium (Cd) and lead (Pb) mass fraction in powdered infant formula based on animal proteins (17th PT). One of the goals was to prepare a material containing Cd around the probable new ML so as to allow participants to test their performance at such a level. The procedure to produce the PT material was set on the basis of the EURL long experience in preparing freeze-dried samples and was tested on a preliminary batch. Homogeneity and stability of the PT material were evaluated through procedures based on international standards. For all tests, a standard deviation for proficiency assessment (σpt), more restrictive than that from the Horwitz equation (σH), was used. The mass fraction of Cd and Pb in the material was proven to be homogeneous and stable for 15 months. These results are extremely satisfactory taking into account the low mass fraction proposed and the restrictive standard deviation for proficiency assessment used to perform the tests. Furthermore, the PT was particularly useful considering that Commission Regulation (EC) 1881/2006 has been recently amended [CR (EU) 488/2014] with the introduction of the new ML for Cd in infant formulas consistent with the mass fraction value proposed in the 17th PT.