Traceability of measurements in chemistry

It is shown from the analysis of metrological validation of all physical quantities measured in chemistry that only for 'concentration' and 'amount of substance' is there no admitted measurement compatibility system like that for other physical quantities. Based on the fundamental notions of metrology, an attempt is made to derive a general concept of traceability and reliability of the measurement of concentration. Special attention is paid to metrological uses of standard samples and reference materials. Specific features of the quantity 'amount of substance' and its unit, the mole, are discussed in terms of metrology.