PREPARATION AND HOMOGENEITY CHARACTERIZATION OF 10 AGRICULTURAL FOOD REFERENCE MATERIALS FOR ELEMENTAL COMPOSITION

Ten agricultural/food reference materials (RM): bovine muscle powder, corn starch, hard red spring wheat flour, soft winter wheat flour, who le milk powder, wheat gluten, corn bran, Durum wheat flour, whole egg powder and microcystalline cellulose, were prepared by milling, irradi ation, sieving, blending and packaging procedures. Homogeneity tests f or 14 elements in randomly selected units were performed by the initia ting laboratories by application of various analytical methods. Al, Ca , Cu, Fe, K, Mg, Mn, Na, Sr and Zn were determined by acid digestion f lame atomic absorption spectrometry, and Cd, Co, Ni and Pb using acid digestion graphite furnace atomic absorption spectrometry after separa tion/preconcentration of the analytes by co-precipitation. In addition , the extensive set of analytical results obtained from the interlabor atory cooperative characterization campaign was assessed to provide ho mogeneity estimates for other elements. Measures of homogeneity were e stimated from the within-laboratory precision from the more precise la boratories. All materials exhibited acceptable homogeneity for virtual ly all 29 elements (Al, As, B, Ba, Br, Ca, Cd, Cl, Co, Cr, Cu, Fe, Hg, 1, K, Mg, Mn, Mo, N, Na, Ni, P, Pb, Rb, S, Se, Sr, V, Zn) for which b est estimate concentration values were available, an essential pre-req uisite in establishing reference values for these materials. Sixty-two percent of all homogeneity coefficients of variation (CV) were below 5%, with Br, Ca, Cl, Mg, Na, P, Zn and especially K and N exhibiting v ery high homogeneity CV less than 1% in some cases.