CIPM MRA COMPARISON REPORTS

The CCQM-K82.2023 comparison was designed to evaluate the level of compatibility of methane in air primary reference mixtures within the range of (1800-2200) nmol mol^-1. The balance gas for the standards was either scrubbed dry real air or synthetic air. This comparison also serves to demonstrate the purity analysis capabilities of NMIs (national metrology institutes) for measurements of trace levels of methane in various matrix gases.

The key comparison involved a simultaneous comparison of a suite of 22 primary gas standards, with two travelling standards prepared by each of the 11 participating laboratories. The standards were sent to the BIPM, where the comparison measurements were conducted. The reference value for a given travelling standard was calculated from a calibration line derived from a self-consistent subset of the standards. Measurements at the BIPM were performed using two independent analytical methods: cavity ring-down spectroscopy (CRDS) and gas chromatography with a flame ionisation detector (GC-FID). In light of the technical issues encountered with our GC-FID, as outlined in Section ANNEX II- Application of GC-FID method to CCQM-K82.2023 travelling standards, it is proposed to utilize the results from the CRDS method for the calculation of the key comparison reference values of the comparison.

The key comparison CCQM-K82.2023 is considered to present an analytical challenge and is therefore classified as a Track C comparison in the CCQM nomenclature.

Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.

The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).