Homogeneity and stability of reference materials

Homogeneity and stability are two crucial characteristics of any certified reference material (CRM). Utmost care must be taken during preparation tn c reate materials as homogeneous and stable as possible. Degradation can gene rally be minimised by reducing the water activity of the material to a leve l between 0.15 and 0.35. However, careful preparation by itself is not enou gh. Positive demonstration of homogeneity and stability is required from th e perspective of implementing uncertainty calculus according to the Guide t o the Expression of Uncertninty in Measurement (GUM). In many cases, homoge neity and stability studies fail to give sufficient quantitative informatio n on homogeneity and stability, mainly because of a lack of measurement rep eatability and insufficient number of replicates. In this work, some soluti ons to these problems and their implications are presented.