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Organic pure substance materials are required in many different fields of analysis, including environmental, food, clinical, pharmaceutical, drugs of abuse, and forensics. For such materials to be suitable for their intended metrological use, the quality of their production must be assured and the value of their purity reliably measured with stated uncertainty. Well-characterized materials are required for the establishment of traceable calibration solutions or direct assay standards as well as to optimize the application of primary ratio methods of measurement such as isotope dilution mass spectrometry or quantitative nuclear magnetic resonance spectroscopy.
The availability of reliable methodology for the characterization of pure materials is thus essential for the establishment of a system of SI-traceable chemical measurement results. In the area of organic analysis, purity is most usefully described in terms of mass fraction of the component of interest present in the material. This can be determined either by approaches that measure the mass fraction or mole fraction of the main component directly, or by "indirect" approaches that identify and estimate the mass fraction of the individual impurities and/or distinct classes of impurities present in the material and, by subtraction, provide a measure for the main component of the material.
Calibration transfer protocols for cases with primary reference measurement procedures and primary calibrators giving metrological traceability to the SI. |
| (Figure 1 of ISO 17511:2003, © ISO, reproduced with permission.) |
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Summary
