International comparison CCQM-K76: Sulfur dioxide in nitrogen

Abstract

The key comparison CCQM-K76 was designed to test the capabilities of the participants to measure and certify sulfur dioxide in nitrogen, and to provide supporting evidence for the CMCs of these institutes for sulfur dioxide. Also, as sulfur dioxide is designated a core compound, and the 100 µmol/mol concentration is within the designated core compound concentration range, this comparison was also designed to demonstrate core capabilities of institutes which qualify under the rules of the Gas Analysis Working Group.The results of all 16 participants in this key comparison, except for three, are consistent with their key comparisons reference values. The three participants which are outside the KCRV interval are NIM, SMU and NPLI. This comparison may be used to demonstrate core analytical capabilities in accordance with the rules and procedures of the CCQM Gas Analysis Working group.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Extrapolation schemes of key comparison results in gas analysis

“…A 'model 2' key comparison mimics the provision of a certified reference material, and for the mixtures concerning in this paper, these uncertainty budgets are based on ISO 6142-1 [20], describing the preparation of calibration gas mixtures by static gravimetry. Examples of uncertainty budgets for gravimetrically prepared gas mixtures in 'model 2' key comparisons have been published in the measurement reports in CCQM-K82 (methane in air) [19] and CCQM-K120 (carbon dioxide in air) [26], and those for the analysis ('model 1') key comparisons in the measurement reports in, e.g., CCQM-K76 (sulphur dioxide in nitrogen) [28] and CCQM-K111 (propane in nitrogen) [13].…”

“…In practice, it is sometimes observed that the standard uncertainty thus obtained does not fully explain the dispersion of the three measured values in a key comparison. As of CCQM-K76 [28], this assessment is part of the uncertainty evaluation. In the beginning, the standard deviation of the three measured values was combined with the standard uncertainty computed from the ISO 6143 procedure.…”

“…This approach addresses in a way the requirement of ISO 6143 to obtain the instrument responses under reproducibility conditions, which is hard to implement practically. Practical calculations using this approach have been shown in various key comparison reports [13,28].…”

Benchmarking the success of CCQM key comparisons for metrology institutes and their stakeholders

“…The filled circles show the results from five track A key comparisons (CCQM-K52: 360 µmol mol −1 carbon dioxide in air [7], CCQM-K53: 100 µmol mol −1 oxygen in nitrogen [8], CCQM-K76: 100 µmol mol −1 sulphur dioxide in nitrogen [9], CCQM-K111: 1000 µmol mol −1 propane in nitrogen [10] and CCQM-K120: 800 µmol mol −1 carbon dioxide in air [11]). Figure 1 does not show the results from comparisons at 380 and 480 µmol mol −1 from CCQM-K120 as they fall outside track A.…”