Thermometry's dependence on chemical metrology: a needs-based assessment

The International Temperature Scale of 1990 assigns temperatures to the solid-liquid phase transitions (triple points, melting points, freezing points) of various substances. Since the ideally pure substances of the definition are unattainable in practice, the influence of impurities must be accounted for. Frequently, this is the dominant uncertainty component in realizing these most important reference temperatures. While a number of methods have been employed to estimate the uncertainty arising from the impurity effect, current thinking appears to have converged on methods that depend on chemical analyses of the materials employed. For the majority of cases, the demands of the thermometry community exceed the capabilities of routine analytical chemistry. It may, therefore, be necessary to consider a concerted action to rigorously characterize homogeneous batches of material using as many techniques as can reasonably be brought to bear on the problem in an effort to develop certified reference materials to serve both the thermometry and chemical metrology communities.