PROGRESS REPORT BY RELEVANT INTERNATIONAL ORGANIZATIONS (Agenda Item 7a)
RELATIONSHIP BETWEEN THE ANALYTICAL RESULT, THE MEASUREMENT UNCERTAINTY AND THE SPECIFICATION IN CODEX STANDARDS (Agenda Item 7b)
52) The Delegation of Ireland informed the Committee that the second edition of the EURACHEM/CITAC Guide Quantifying Uncertainty in Analytical Measurement had been published. The changes dealing with the use of method performance data and method validation data in order to determine the components of uncertainty were of particular importance to the Committee. The Delegation pointed out that the examples had been revised and that the Guide also included a new section on traceability. It was noted that a summary was included in document CX/MAS 01/8 and that the complete Guide was available from the EURACHEM website: http://www.vtt.fi/ket/eurachem
53) The Delegation of Finland also informed the Committee that the NMKL procedure for the expression of measurement uncertainty was under revision and would be harmonized with the EURACHEM Guide.
54) The Delegation of the United Kingdom, while presenting the document, highlighted the main issues to be addressed: the terminology, the methodology to estimate measurement uncertainty and its incidence on the interpretation of the result and the assessment of compliance. The Delegation pointed out that the term uncertainty was now widely accepted in the analytical community; that laboratories complying with the principles of laboratory quality did not need a further estimate of the measurement uncertainty according to the ISO component-by-component approach, and that results should be generally reported with the measurement uncertainty. The Committee also noted that the ISO/IEC Guide 25 (endorsed by Codex) had been replaced by ISO/IEC 17025, which referred to measurement uncertainty.
55) The Committee considered the Recommendations presented at the end of the document and agreed that they should be drafted as Guidelines on Measurement Uncertainty intended for governments, to be circulated at Step 3, subject to approval as new work by the Commission. The Committee had an extensive discussion and made a number of amendments and additions to the initial text.
56) The Introduction was reworded for clarification purposes and to reflect the importance of the issue. Some delegations questioned the provision that “food analysis laboratories are required to be in control”. The Delegation of the United Kingdom pointed out that this was a well understood expression to reflect that laboratories applied Codex principles related to the quality of laboratory results.
57) The Delegation of Finland made the following proposals in order to clarify the text; in point 1) the measurement uncertainty should be “estimated” rather than “quantified”; in point 2) it would be preferable to refer first to data available through the use of internal quality control; in point 4) reference to single-laboratory validation could be included.
58) The Delegation of the United States, supported by the Delegation of Thailand, expressed the view that, as measurement uncertainty was a relatively new concept, it might not be well known in some countries, and the Committee should therefore recognize that “reliability” might still be used. The Delegation of Ireland pointed out that “uncertainty” was an accepted term at the international level and that Codex was a reference in international trade, and proposed that the ISO definition should be used with an appropriate explanation in the text of the Guidelines.
59) The Committee agreed to include the ISO definition of measurement uncertainty in order to clarify the issue of terminology. As a compromise, an explanatory note was added in square brackets after Note 3) to reflect that “measurement reliability” might also be used.
60) The Observer from IOFI indicated that the question of measurement uncertainty was especially important for the analysis of compounds which were present at low concentrations like flavours, as related to statutory provisions or compliance with specifications. The Committee noted that the question of compliance had also been discussed in relation to recovery factors and would need to be addressed from a general perspective (see also para. 64).
61) The Committee agreed to merge Recommendations 3 and 4 as they both referred to the methodology used to evaluate uncertainty. The Delegation of the United States proposed to add an additional sentence to indicate how the overall uncertainty might be determined.
62) The Delegations of Spain and Uruguay pointed out that the term “reliability” had negative implications and should not be used in Spanish. It was therefore important to specify that the expression used should be equivalent to “uncertainty” and had the same meaning. The Committee agreed to refer to an “alternative, equivalent term” and noted that member countries would have the possibility to make comments on the appropriate terminology in different languages. The Delegation of Ireland informed the Committee that the journal Accreditation and Quality Assurance (AQAL) (Volume 1, No. 1, January 1996) included a Glossary of Analytical Terms in which “uncertainty of measurement” was translated into several languages.
63) The Committee agreed to circulate at Step 3 a first draft of the Proposed Draft Guidelines on Measurement Uncertainty for Governments, as attached in Appendix V, subject to approval by the Commission as new work.
64) The Delegation of the United Kingdom proposed to prepare a discussion paper addressing the compliance aspects associated with measurement uncertainty, recovery factors and sampling since these different issues were related, and invited interested delegations to participate in the preparation of the paper. The Committee welcomed this proposal as there was a need for practical guidance to governments and food control laboratories in this area, and agreed to consider this question at the next session (see para. 60).
