Honey as a material for proficiency testing

Abstract

Honey is widely analysed by many European Union control laboratories for heavy metals in foodstuffs. No maximum levels are set for cadmium and lead in this matrix, but most of the member states include this analytes–matrix combination in their National Residue Monitoring Plans setting specific action levels. The need to harmonize these values is under consideration within the European Commission. The lack of suitable certified reference materials as well as the scarcity of appropriate proficiency testings imply a difficulty for the official and National Reference Laboratories in the assessment of their method performance. The European Union Reference Laboratory for Chemical Elements in Food of Animal Origin organized the 19th PT on the determination of cadmium and lead in honey giving its network the possibility of checking the performances of the analytical methods used. An adequate procedure for the preparation of honey material spiked with cadmium and lead at values of mass fraction of interest (roughly 20 and 100 µg kg⁻¹ for cadmium and lead, respectively) was developed. A commercial wildflower honey was spiked at proper concentration levels, achieving suitable fluidity and homogeneity by mild heating and stirring. Homogeneity and stability were investigated using an ad hoc validated analytical method and the PT material was found homogeneous and stable, covering the time span of the interlaboratory comparison. These outcomes as well as the good agreement between the assigned values and the values obtained from the homogeneity test confirmed the effectiveness of the procedure for the production of the material and the fitness of the material for the purpose of this PT.