Measurement standards and the general problem of reference points in chemical analysis

Apart from the measurement standards available in general metrology in the form of the realizations of units of measurement, measurement standards for chemical composition are needed in the vast field of measurements of chemical composition, because the main aim of such measurements is to quantify non-isolated substances, often in complicated matrices, to which the ''classical'' measurement standards and their lower-level derivatives are not directly applicable. At present, most chemical measurement standards are material artefacts. But not all of these artefacts are measurement standards according to the metrological definition, i.e. firmly linked to the SI unit in which the chemical composition represented by the standard is expressed. In fact, only a very restricted number of really reliable chemical measurement standards is available at present. Since it is very difficult and time-consuming to substantially increase this number and, on the other hand, reliable reference points are increasingly needed for all kinds of chemical measurement, primary methods of measurement and high-level reference measurements as well as primary measurement devices and procedures will play an increasingly important role for ensuring world-wide comparability and hence mutual acceptance of chemical measurement results.