A (r)evolution in analytical chemistry
The development of analytical chemical measurement techniques has exploded over the last forty years because of the development of fast and sensitive instrumental and automated measuring systems and the broad use of chemical measurement results. This has occurred in the clinical field, in the worldwide control of nuclear materials, in intercontinental trade and commerce (prompted by chemical pollution of food and drinks), and in safeguarding of the environment in general.
Thus, chemists consistently require answers to the crucial questions: when are results of chemical measurements metrologically comparable, i.e. metrologically traceable to a common reference?1 What are the requirements for metrological traceability of such results, i.e. “the property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty?” What is the metrological equivalence of such results? ISO/IEC 17025 now requests “metrological traceability” of measurement results to be established and that alone has generated a quick and large interest in matters of traceability.2
The establishment of worldwide agreement on “metrological comparability of measurement results” has been very challenging. Until recently there has been little conceptual discussion on the basic structure of an analytical measurement and its elements, although articles in Accreditation and Quality Assurance, and Journal for Quality, Comparability and Reliability in Chemical Measurement, have helped considerably to disseminate new concepts developed in the international vocabulary of metrology.1 Laudable attempts have also been made by EURACHEM and CITAC in their guides.3
IUPAC’s response to this challenge
In 2001, the Analytical Chemistry Division initiated a project to study the meaning and structure of “traceability” in chemical measurement (IUPAC project 2001-010-3-500). It has involved establishing a basic conceptual structure of an analytical measurement.
Following extensive study, numerous drafts, and extensive examinations by external reviewers, the results of this decade-long study are now available in Pure and Applied Chemistry.4 The external review process was a valued contribution and led to new definitions of concepts not even foreseen in the VIM and such as “metrological reference” or “metrological equivalence of measurement results.”
It would be optimistic to conclude that the concepts developed in this project are already widely accepted and applied; clearly more time is needed for that. However, there are now more frequent references to metrological traceability. Reviewers of scientific papers also start to ask for proof of traceability and the relationship between measurement uncertainty and metrological traceability appears to be better understood. The IUPAC project task group looks forward to a lead by IUPAC through implementing the results of this study in Pure and Applied Chemistry.
The task group views this topic as an ongoing challenge and would welcome comments from readers.
The support by former Analytical Chemistry Division President Kip Powell, is gratefully acknowledged, both for his encouragement at the start of this project, as well as for his support during execution.
1. International Vocabulary of Metrology – Basic and general concepts and associated terms (VIM) edn 3, JCGM 200:2012 ; www.bipm.org/vim
2. ISO/IEC 17025:2005, General requirements for the competence of calibration and testing laboratories, 2nd edn, International Organization for Standardization (ISO), Geneva.Google Scholar
3. EURACHEM/CITAC guide; www.nmschembio.org.uk/PublicationArticle.aspx?m=115&amid=1202 (accessed 2014-02-19)
4. Paul De Bièvre, René Dybkaer, Ales Fajgelj, and D. Brynn Hibbert, Metrological traceability of measurement results in chemistry—concepts and implementation, Pure and Applied Chemistry 83 (2011) 1873-1935; http://dx.doi.org/10.1351/PAC-REP-07-09-39Web of ScienceCrossref