Homogeneity of Reference Materials†

Abstract

Homogeneity is that attribute of a sample which assures that analysis of all subsamples taken for measurement will produce the same analytical result, within measurement uncertainty. In reality, all geological samples are heterogeneous to some degree, for some constituent elements. The nugget effect for gold and the platinum group elements is the most obvious example. The fundamental issue is not whether heterogeneity exists, but whether it is detectable, given the number of measurements made, the sample size taken for each, and the inherent repeatability of measurement for the method used to assess heterogeneity. In establishing reference values for reference materials, the contribution of detectable heterogeneity to the overall uncertainty of individual reference values must be quantified.