Report on International
Bureau of Weights and Measures (BIPM)Committee for Amount of
Substance (CCQM) Working Group Meeting and Workshop on Measurement
29 November-3 December 1999
Dr. Ales Fajgelj [Quality Assurance Supervisor, International Atomic
Energy Agency (IAEA) Laboratories, A-2444 Seibersdorf, Austria; E-mail:
[email protected]], Chairman
of the IUPAC Interdivisional Working Party on Harmonization of Quality
Assurance Schemes for Analytical Laboratories, has submitted the following
As a successor to Prof. Folke Ingman in the position
of IUPAC representative to the Consultative Committee for Amount of
Substance (CCQM), International Bureau of Weights and Measures (BIPM),
Paris, France, I attended a working group meeting and a workshop on
measurement uncertainty held 29 November- 3 December 1999 at BIPM.
General Information and Observations
CCQM is a technical committee that operates as
a part of BIPM, a central international metrological organization.
CCQM was established in 1993 to support the BIPM mandate in
establishing fundamental standards and
scales for measuring principal physical quantities and maintaining
carrying out comparisons of national and
ensuring coordination of corresponding
measurement techniques, and
carrying out and coordinating measurements
of fundamental physical constants relevant to these activities in
the field of chemical measurements.
Working Groups (WGs) carry out the technical work
of CCQM. Present WGs are grouped in two fields, as follows: i) primary
methods, such as isotope dilution mass spectrometry, coulometry, static
and dynamic analysis of gas mixtures, titrimetry, determination of
freezing point depression, and NMR spectroscopy as a primary method;
and ii) international comparisons, including key comparisons, organic
analysis, inorganic analysis, gas analysis, and pH. In one of the
most important events related to international metrological harmonization
in the last decade, 49 countries signed the Mutual Recognition Arrangement
(MRA) in October 1999. The MRA provides a formal basis for mutual
acceptance of national measurements standards and of calibration certificates
issued by national metrology institutes.
To assure and demonstrate the comparability (reproducibility
of measurement results) between the measurements carried out by respective
national metrological institutions, many international comparisons
are being organized. Each international comparisonkey comparisonis
first organized as a pilot study. Several metrological institutions
take part in the characterization of a selected material and establish
the best estimate of a "true value" for analytes of interest
and a target value for the associated measurement uncertainty. Although
metrological comparisons organized by CCQM are not intended for production
of reference materials, the technical principles are exactly the same.
For this reason, such work carried out by CCQM
is of great interest to IUPAC in general and especially to IUPACs
Analytical Chemistry Division and its Interdivisional Working Party
on Harmonization of Quality Assurance Schemes for Analytical Laboratories.
In most cases, those institutions participating in pilot studies are
also the main reference materials-producing organizations, e.g., National
Institute of Standards and Technology (NIST), Institute for Reference
Materials and Measurements (IRMM), LGC, etc. The results of pilot
studies are discussed within WGs, and all the technical reasons for
eventual discrepancies are investigated before any outliers are identified
and before any decision on acceptance of results is taken. I participated
in the work of the WGs on Organic Analysis and Inorganic Analysis
and at the workshop on measurement uncertainty organized in the framework
of this CCQM meeting. Some of the following points raised during a
discussion in the WGs or at the measurement uncertainty workshop might
be of interest to IUPAC members; for example:
At the WGs discussion of international laboratory
For complicated analyses
or when the complete material has to be used, more than one sample
bottle (vial) is provided to the participants. One bottle is provided
for training purposes.
There is no general guidance
on how participants data should be statistically treated. Arithmetic
mean, weighted mean, median, and total median are used to express
the best estimate of a "true value" on the basis of the
organizers decision in each comparison separately.
Criteria for data acceptance
in international key comparisons are set up during pilot studies.
They are established by a small number of laboratories (with demonstrated
quality). The measurement capability of these laboratories has to
be demonstrated at regular intervals (at least once per year). Pilot
studies should define "what is reasonably achievable".
in pilot studies can withdraw their data at any time. Laboratories
participating in key comparisons cannot withdraw data after submission.
Large differences in perception
between the theoretical and practical approaches related to the traceability
of analytical results exist even between metrological institutions.
Problems with inhomogeneity
of intercomparison samples are often observed.
Problems with shipment of
some types of materials (liquid samples on trans-Atlantic flights,
customs regulations, etc.) are often reported.
The extent of instructions
given to the participants was discussed. Regardless of the instructions
given, there are always some laboratories that are not following the
Most of the discussion points are still open questions.
No general answers were provided, and there is still a lot to do in
the harmonization of these open questions. At this CCQM meeting, an
important change in the perception and classification of primary methods
of analysis was observed. The potential of all techniques to demonstrate
traceability of measurement results obtained to the International
System of Units (SI) should be reinvestigated. It was pointed out
that analytical techniques could not be declared as primary per
se. Their potential should be demonstrated for each sample/ measurand/analyte/technique
combination. For this reason, as a first step in this direction, an
international symposium was planned for April 2000 at BIPM. In connection
with the "single-laboratory method validation principle"
proposed and discussed at the AOAC/FAO/
IAEA/IUPAC Workshop in Budapest in November 1999, this new perception
of primary methods of analysis is very promising for different analytical
techniques. Being declared as primary and accepted as fully validated,
analytical techniques might be applied to a wide range of analysis
required for legislative and international trading purposes.
As agreed before the meeting, I had the opportunity
to meet individually with Dr. Terry Quinn, Director of BIPM; Dr. R.
Kaarls, CCQM President; and Dr. R. Davis, CCQM Executive Secretary.
In all cases, the importance of international
cooperation in the field of chemical metrology was pointed out. The
relationships between BIPM, CCQM, and IUPAC were found to be successful.
National and international needs relating to metrology are well elaborated
in the report prepared by BIPM for governments of Member States of
the Convention of the Metre in 1998. (Copies are available free of
charge from BIPM.) It was pointed out that IUPAC input into metrology
in chemistry might even be larger.
The next meeting of CCQM took place 4-7 April 2000 at BIPM in Sèvres,
France. It was combined with the working group meetings and with the
international symposium on primary methods. For more information about
BIPM and CCQM, visit the BIPM web site at http://www.bipm.fr/.