CHARACTERIZATION OF A FUNGUS REFERENCE MATERIAL, AND A GUIDE FOR USE

A reference material consisting of an edible fungus, Cantharellus tubaeformis, with certified levels of Pb, Cd, Zn, Cu, Mn, Cr, Ni, Co and Fe was produced, primarily for use in a project concerning metal determination in common edible fungi. The C. tubaeformis was dried, homogenised and sieved using non-contaminating equipment. It was then mixed thoroughly before bottling in polythene containers. Homogeneity was checked by multiple analysis of a number of containers, and was found to be satisfactory. Each metal was determined by at least two different methods of analysis. A total of ten laboratories participated in the certification process. All the metals analysed in this certified reference material showed good agreement with the levels found in fresh C. tubaeformis, when the difference in water content was accounted for. This indicates that no contamination of the fungus reference material occurred during the production. It is concluded that the 95% confidence interval for the true mean, as defined for the different metals, is of limited value from the user's point of view. Therefore, a more user-oriented way of presenting the results, based on the within- and between-laboratory standard deviations of the certification process, is suggested. These are 95/95% tolerance intervals within which the user's results should fall. Different intervals are given, one of which indicates the largest acceptable difference between duplicates and another for the acceptable range of future means.