Ad hoc material for proficiency testing: freeze-dried liver

One of the tasks of European Union Reference Laboratories (EURLs) for feed and food is the organization of proficiency testing (PTs) for the network of National Reference Laboratories (NRLs) of EU member states according to the area of competence. This crucial assignment leads the EURL for Chemical Elements in Food of Animal Origin (EURL-CEFAO) to plan PTs that include various chemical element/matrix/concentration combinations in order to organize a profitable exercise for its network. The purpose of this paper was to describe the “step-by-step” preparation of a PT material and the efforts of an EURL to provide proper test items to national laboratories (NRLs). The exercise was tailored to train participants and give them the opportunity to practice around the maximum levels (MLs) set in EU legislation, values at which sample acceptance is the critical issue. The EURL strategy has been chosen considering the role of the NRLs that could be summoned as third party in legal controversies. A PT on the determination of cadmium and lead in freeze-dried liver was then scheduled. The goal was to achieve a sample with a mass fraction (w) of the elements around the ML (0.50 mg/kg for both). Preliminary studies allowed the EURL to calculate the amount of spike to reach the target mass fractions. The target Cd and Pb mass fractions were in good agreement with the contents found in the frame of the homogeneity test as well as with the consensus values derived from the results reported by the PT participants. This proved the suitability of the production procedures and the quality of the delivered PT test items.