Reference materials--a main element in a coherent reference measurement system.

The analytical reliability of any measurement procedure requires a specifically designed, coherent reference measurement system, including interrelated measurement procedures and measurement standards such as reference materials. The latter may be characterized by three sets of characteristics. The general characteristics comprise origin, mode of production, physical state and phase, homogeneity, physical form, container, additives, storage conditions, stability, and dangerous properties. The specific characteristics describe molecular composition, analyte, purity, matrix, quantity of interest (including scale), assigned value, and uncertainty of measurement. The additional characteristics concern the way in which values for other characteristics were obtained, the hierarchical position of the material, certificate, instructions for use, and intended function. The problem areas of reference materials comprise definition of the appropriate analyte, purification, matrix, assignment of values, and nomenclature. The present ambiguous terminology is presented and a systematic structure of descriptive names is proposed (tab. 1).