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

A reference material consisting of an edible fungus, Cantharellus tuba eformis, with certified levels of Pb, Cd, Zn, Cu, Mn, Cr, Ni, Co and F e was produced, primarily for use in a project concerning metal determ ination in common edible fungi. The C. tubaeformis was dried, homogeni sed and sieved using non-contaminating equipment. It was then mixed th oroughly before bottling in polythene containers. Homogeneity was chec ked by multiple analysis of a number of containers, and was found to b e satisfactory. Each metal was determined by at least two different me thods of analysis. A total of ten laboratories participated in the cer tification process. All the metals analysed in this certified referenc e material showed good agreement with the levels found in fresh C. tub aeformis, when the difference in water content was accounted for. This indicates that no contamination of the fungus reference material occu rred during the production. It is concluded that the 95% confidence in terval for the true mean, as defined for the different metals, is of l imited value from the user's point of view. Therefore, a more user-ori ented way of presenting the results, based on the within- and between- laboratory standard deviations of the certification process, is sugges ted. These are 95/95% tolerance intervals within which the user's resu lts 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.