Use of Quality Control Measurements to Determine Measurement Uncertainties according to ISO and EURACHEM Guides

Statements of analytical measurement results are not complete without sufficient information about the measurement uncertainty. Standard methods for evaluating and expressing measurement uncertainties require detailed knowledge of the error structure in terms of individual uncertainty components associated with each step of an analytical procedure and their mutual correlation. Many uncertainty components must be determined experimentally by the laboratory and are only valid for the particular setting. Frequently, this relies on repeated determinations of reference materials during the validation of a method and during its ongoing quality control. The validity of such estimates is limited by the reliability of the reference materials and the degree to which they are representative for the actually tested materials. The structure and assessment of uncertainties of reference materials is not always sufficiently stated. The paper demonstrates the evaluation of the measurement uncertainties for the elemental assay of plutonium by IDMS, with special regard to the mentioned problems.