International Comparisons for Chemical Measurements

Because of NIST's role as the National Metrology Institute (NMI) in the U.S., the Analytical Chemistry Division's measurement capabilities must be benchmarked against the capabilities of NMIs worldwide as required by a Mutual Recognition Arrangement (MRA) established in 1999. The MRA provides a framework for obtaining reliable quantitative information on the comparability of measurement services provided by all NMIs, thereby providing governments and other parties with a technical foundation for wider agreements related to international trade, commerce, and regulatory affairs. The Analytical Chemistry Division actively participates in the International Committee of Weights and Measures (CIPM) Consultative Committee for Amount of Substance-Metrology in Chemistry (CCQM) comparisons, which address chemical measurement-related issues important for international trade, environmental, health, and safety-related decision making. We have also established a limited number of strategic bilateral collaborations and/or intercomparisons with NMIs around the world to demonstrate comparability of measurements and/or to cooperate in the development of reference materials.

International agreements and decisions concerning trade and our social well-being increasingly require mutual recognition of measurements and tests among nations. The absence of such mutual recognition is considered a technical barrier to trade and an impediment to environmental and health-related decision-making. In recent years, mutual recognition agreements have been established related to testing and calibration services with the bodies accrediting such activities. All of these agreements rest upon the assumption of equivalence of national measurement standards and the reliability of the link between national measurement standards and the relevant testing services in each country. In October 1999, the directors of NMIs for the 38 member states of the Meter Convention and 2 international organizations signed the mutual recognition arrangement (MRA) on national measurement standards and calibration and measurement certificates issued by NMIs; 34 additional countries and associates have since signed the MRA. The MRA provides an open, transparent, and comprehensive framework for obtaining reliable quantitative information on the comparability of measurement services provided by the signatory NMIs. Signatories to this MRA have the following responsibilities: (1) declaring and documenting their calibration and measurement capabilities (CMCs) in Appendix C of the MRA, (2) participating in relevant international comparisons to benchmark the claims made in the CMCs (MRA Appendix B), and (3) documenting the existence of a system for assuring the quality of the measurement services provided. NIST has taken a leadership role in the International Committee of Weights and Measures (CIPM) Consultative Committee for Amount of Substance – Metrology in Chemistry (CCQM) and the Chemical Metrology Working Group of the Interamerican System for Metrology (SIM) to assure the effective, fair, and metrologically sound implementation of this MRA. 

The CCQM has seven working groups: (1) Gas Analysis, (2) Organic Analysis, (3) Inorganic Analysis, (4) Electrochemistry (5) Bioanalysis, (6) Surface Analysis, and (7) Key Comparisons. These working groups are responsible for selecting and overseeing the operation of Key Comparisons, in which participating laboratories demonstrate their measurement or material preparation capabilities. Members of the Analytical Chemistry Division are involved in the various activities within all but one of the seven working groups. The International Bureau of Weights and Measures (BIPM) database includes 4287 CMCs for chemical measurements. About 975 are from NIST. Since 1993 108 key comparison studies and a similar number of pilot studies have been conducted under the auspices of the CCQM to underpin CMC claims. The Analytical Chemistry Division has participated in 70 Key Comparisons, serving as the Coordinating Laboratory in approximately 30 key and pilot studies. The recent CCQM activities for the organic, inorganic, electroanalytical, and gas CCQM working groups are provided in project descriptions.

Participation in CCQM Key Comparisons is generally limited to NMIs with well-established chemical metrology programs. Within the Americas, only the U.S., Canada, and Mexico have well-established programs. To effectively address the unique needs of all 32 countries within SIM, whose capabilities in chemical metrology span a very broad range, the SIM program has focused on training and capability assessment rather than participation in MRA-driven Key and Supplemental Comparisons. Since 2002, 13 intercomparison exercises have been carried out to assess the proficiency of SIM NMIs and/or their designated laboratories, and the Analytical Chemistry Division has served as the coordinating laboratory for many of these studies.

In addition to these global and regional activities, we have also establishing a limited number of strategic bilateral collaborations and intercomparisons with NMIs around the world. For example, since 1992 we have collaborated with the Netherlands Measurement Institute (NMi) to determine the equivalence of primary gas standards resulting in a formal "Declaration of Equivalence" that is recognized by the U.S. EPA and European environmental regulatory bodies as documenting the equivalence between 12 NIST and NMi primary gas mixture suites. In December 2007 an agreement was signed between NIST/CSTL and the European Commission’s Joint Research Centre (JRC) Institute for Reference Materials and Measurements (IRMM) in Geel, Belgium to collaborate and coordinate with their research and development programs in metrology. This agreement includes cooperative research on modern measurements and their quality assurance, and technical cooperation in the preparation and characterization of certified reference materials. The JRC and NIST/CSTL will also share resources and work to harmonize views within international metrology bodies where both organizations carry responsibilities in relation to chemical metrology, biometrology, and international measurement standards. Technical representatives from CSTL and IRMM will meet regularly to coordinate activities of mutual interest. In 2007 we started a collaborative effort with the National Institute of Metrology, Standardization and Industrial Quality (INMETRO), the National Metrology Institute of Brazil, to develop biodiesel and bioethanol CRMs. In addition to the formal agreements described above, we have several informal collaborations with other NMIs including extended visits of scientists from these other NMIs to work at NIST for periods of several months to a year.