Role of reference materials for the realization of physicochemical properties. Past, present, and future

Reference materials have long been considered essential for both calibratio n and checking the correct operation of equipment used for the determinatio n of physicochemical properties. Up until the 1970s, the maintenance of pur e reference materials and the means to verify their properties through meas urement using state-of-the-art equipment was the prerogative of many nation al standards laboratories. Over the last 30 years, many of the standards la boratories have either limited or eliminated their activity in maintaining both reference materials and state-of-the-art measuring equipment. One reas on is the ready availability of high-purity materials from commercial sourc es and the ease with which one can now determine purity. A second reason is the ready availability of instruments to measure digitally fundamental qua ntities such as time, temperature, length, frequency, and voltage accuratel y has enabled chemical calibration using reference materials to be replaced in many instruments by electrical calibration. At the same time, digitizat ion has enabled the computerization of the whole measurement process. Such automated devices, if not checked with reference materials, can give highly reproducible results but have large systematic errors, leading to poor val ues. The role of physicochemical reference materials in the past and the pr esent will be outlined, and their status in the future will be explored.