Looking back at two decades of “Metrology in Chemistry”

Abstract

In this Editorial, I am announcing the end of my 16 years of formal responsibility for this Journal as I am becoming slightly subject to biological boundary conditions imposed by mother nature. During that time period—and even prior to that—I was privileged to be in a position from where I could observe a growing interest for the introduction of metrological principles in chemical measurement and could follow this evolution closely at many stages and in many environments. Maybe this is a good time to look back on these years and offer some thoughts for the future of ‘‘Metrology in Chemistry’’, a concept quoted so many times in this Journal. Somewhere in the period 1985–1990, an important change in thinking and attitude must have occurred within the SI [1] about chemical measurement. It must have been a difficult undertaking since it took quite some time after the introduction in 1971 of an SI unit intended for chemical measurement, the mole. For much longer, other measurement units such as length, mass, time, electric current, thermodynamic temperature, and luminous intensity, were part of the SI structure through Consultative Committees to the CIPM (see ‘‘Appendix’’). The change in thinking eventually resulted in the foundation of the CCQM (see ‘‘Appendix’’) which had its first session in 1995 [2, 3] 24 years later. It is noteworthy that the name ‘‘CCQM’’ contains ‘‘amount-of-substance’’, a not well described nor commonly well understood quantity amongst chemists, not then and not until this very day. A broader view was reflected by the addition of ‘‘metrology in chemistry’’ in the name of CCQM in 2002. That seemed to include, at least implicitly, any ‘‘chemical measurement’’. However, no in-depth conceptual discussion about the ambiguous quantity ‘‘amount-of-substance’’ nor about ‘‘chemical measurement’’ has taken place in the CCQM as yet. Such a discussion is very necessary and therefore highly recommended. ‘‘Amount-of-substance’’ is a base quantity of the international system of quantities ISQ. For lack of a better term, it is sometimes described as ‘‘the quantity for which the mole is the unit’’, a remarkable reasoning as long as ‘‘amount-of-substance’’ is commonly not well understood. Actors in the field of physical chemistry, especially in thermodynamics, seem to have been the main if not only proponents of a unit ‘‘mole’’ in 1971, involving the Physical Chemistry Division of the IUPAC (see ‘‘Appendix’’). Analytical Chemistry was not really involved—nor did analytical chemists involve themselves—very much. Neither are they very noticeable in the presently ongoing discussions on the re-definition of the mole. However, the development of chemical measurement techniques exploded over the last 40 years because of the broad use of chemical measurement results in intercontinental trade and commerce, caused by possible pollution of food and drinks, and of the environment in general. Thus, fast instrumental measuring systems were needed as well as an answer to the question ‘‘when are results of chemical measurements comparable throughout the world and, if so, what is their degree of equivalence?’’ (concept 5-4 in [4]). This (r)evolution has been achieved by analytical chemists mostly outside the ‘‘metrological community/structures’’. The technical development was based on the particulate nature of atoms and molecules that were converted into charged particles or light emission/absorption quanta in an essentially one-to-one ratio, in all kinds of spectrometers. Thus, the concept ‘‘number-of-entities’’ was confirmed again to be a highly relevant quantity because it was the P. De Bievre (&) Kasterlee, Belgium e-mail: paul.de.bievre@skynet.be