CCQM-K68.2019, Nitrous Oxide (N2O) in air, Ambient level Final Report

The key comparison CCQM-K68.2019 was aimed at evaluating the level of comparability of laboratories’ capabilities for preparing nitrous oxide in air primary reference mixtures at ambient amount fractions, in the range 320 nmol mol−1 to 350 nmol mol−1. The comparison was coordinated by the BIPM and the KRISS. It consisted in the simultaneous comparison of a suite of 2n primary gas standards, two standards to be prepared by each of the n participating laboratories. Two independent analytical methods were used by the BIPM to analyse the amount fraction of N2O in air, namely Gas Chromatography with an Electron Capture Detector (GC−ECD) and Quantum Cascade Laser Absorption Spectroscopy (QCLAS). Since the circulation of the Draft A report in April 2021, four meetings took place with participants to discuss the mathematical treatment of the comparisons results, and several models were proposed. The model chosen by participants is the Bayesian Errors−In−Variables regression with shades of dark uncertainty. In this final report, the Key Comparison Reference Values were obtained with this model, with calculations performed by B. Toman and A. Possolo. The key comparison CCQM-K68.2019 is considered to present an analytical challenge and therefore classified as Track C comparison in the CCQM nomenclature.