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This document provides guidelines for the evaluation of the purity of organic chemicals, usually high-purity chemicals, intended for use as reference materials and for the certification of these materials such that assigned values can be considered as metrologically sound and traceable to base units of mass and amount of substance. The existing methodology for the analysis and certification of high-purity reference materials is presented in sections on metrological concepts and nomenclature, procedures used for preparation and certification of high-purity reference materials including analytical methods, and the appropriate combining of different measurements. The consequences of decisions on required purity, the nature of allowed impurities, traceability to other standards, quantitative characterization, measurement uncertainties, and what information needs to be included in a certificate are considered. A general approach to the assessment of purity is proposed. The approach includes the determination of what is required for a material to be fit for its intended use, the identification of impurities, the determination of purity by direct or indirect means with a discussion of appropriate analytical techniques, the combining of various analytical results, and the proper presentation of available information. The certificates for a number of materials are evaluated against this approach as case studies. Four opportunities for research that would enhance the infrastructure available for methods applicable to creating traceable high-purity organic standards are identified. These are: 1) the creation of a limited set of certified materials for quantitative nuclear magnetic resonance, 2) the generation and evaluation of data that would permit estimating uncertainties for measurements based on relative signals from techniques such as gas chromatography and quantitative nuclear magnetic resonance applied to the determination of impurities, 3) the improvement of the prediction of chromatographic detector response factors through the use of quantitative structureproperty relationships, and 4) the development of a sensitive universal mass detector for liquid chromatography with isotope ratio mass spectrometry and chemical reaction interface mass spectrometry as promising candidates.

An approach to the metrologically sound traceable assessment of the chemical purity of organic reference materials