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Role of neutron activation analysis in the preparation and certification of reference materials

Reference materials (RMs) and certified reference materials (CRMs) are an important tool in achieving measurement compatibility. One of the possible approaches in producing such materials is organization of world-wide interlaboratory comparisons. The sequence of actions that have to be taken in order to prepare and certify a reference material for multielement inorganic trace analysis is described and discussed. The significance of careful supervision by the person responsible for all the steps starting from choice of the material and sampling, through various stages of preparation down to analysis, evaluation of results, and final assigning of `recommended' (certified) and `information' values is emphasized. The significance of using the proper method of data evaluation and proven criteria for assigning `recommended' (certified) values is discussed in detail. It is shown on several examples that neutron activation analysis (NAA) plays a very important and sometimes unique role in the homogeneity checking and certification of reference materials. Some approaches enabling independent validation of the `recommended' or `information' values assigned in the process of certification are demonstrated.