Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Chemistry and the International System of Weights and Measures Symposium at the ACS National Meeting; Boston, MA, August 19, 2015: Presentations

Symposium Introduction:

Session I: The Consultative Committee on Metrology in Chemistry and Biology: Who We are, What We Do, and Why You Should Care

Important decisions in trade, health care, the environment and food safety and quality are dependent on reliable and accurate chemical and biological measurements. Certified reference materials (CRMs) and reference measurement methods, developed by National Metrology Institutes (NMIs) provide stated references upon which analytical laboratories can anchor their measurement results. The traceability of measurement results to internationally accepted stated references, together with their stated measurement uncertainties, provide the basis for their comparability and global acceptance. Global activities to develop a system for the international equivalence of chemical and biological measurement standards are being led by the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM). The Committee, established in 1993, coordinates work to establish the equivalence of chemical and biological standards from over 50 laboratories in 39 different countries. In order to do this the Committee has organized over 230 inter-laboratory comparisons since its creation, leading to the international recognition of almost 6000 measurement capabilities from these laboratories, which are listed and searchable in the BIPM key comparison database. The CRMs and measurement services cover seven technical areas (organic, inorganic, gas, surface, electrochemical analysis as well as bioanalysis and microbiology) and fifteen measurement service categories ranging from high purity chemicals, to advanced materials, biological materials and nano-materials. The session included presentations on the history, strategy and achievements of the CCQM and descriptions of its impact in the healthcare, environmental and nutrition and food safety areas.

Session II: Redefinition of the International System of Units


The International System of Units (Système International d'Unités, with the international abbreviation SI) is globally accepted as a practical framework for reporting measurement results. The SI consists of a set of base units, prefixes, and derived units—many with special names. The SI base units are unambiguously defined and, by convention, are regarded as dimensionaly independent: the metre, the kilogram, the second, the ampere, the kelvin, the mole, and the candela. The SI is not static but has evolved to take advantage of advances in science and technology. The definitions of the base units can change but a continuity condition is imposed on new definitions to ensure that previously-reported experimental results remain valid. Thus the effect of the change in the definitions will be largely imperceptible when it happens. Experiments to determine the values of certain constants of nature have now evolved to such an extent that redefining four of the base units in terms of fundamental constants more appropriate to the science and technology of our century is envisaged and expected in 2018. Besides the kilogram, the changes to SI definitions are also expected to include the unit for amount of substance, the mole. These two units, the kilogram and the mole, are arguably of most interest to the chemist. The session included a review of quantities, units and measurement uncertainties required in chemical measurements, and the impact of the change in definitions on practical chemical measurements. Experiments designed to accurately measure the fundamental constants involved were described. These experiments are important because they can then be used to realize the new definitions of SI units, including the mole and the kilogram, to the highest accuracy that is possible at present.


Created July 7, 2015, Updated June 2, 2021