Discussion on homogeneity assessment of reference materials based on uncertainty comparison method

An uncertainty comparison method is proposed to assess the homogeneity of reference materials. The method compares “standard uncertainty associated with between-unit variability” (ubb) with “target standard uncertainty” (utrg) or “measurement uncertainty” (umeas) to solve the problems in assessing homogeneity of reference materials. Methods for the calculation of ubb, utrg and umeas as well as criterion for the quantitative judgment of sample homogeneity are introduced. When ubb ≤ 0.3utrg, it shows the sample is considered to be homogeneous; when 0.3utrg < ubb ≤ 0.7utrg, the sample is considered to be sufficiently homogeneous for the intended use; and when ubb > 0.7utrg, the sample is considered to be inhomogeneous. The uncertainty comparison method is compared with the F test method and shown to be more objective for the assessment of the homogeneity of certified reference materials for the chemical testing of toys.