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To develop a 100 μmol mol −1 hydrogen chloride (HCl) primary standard gas mixture in a high-pressure cylinder, pure HCl gas was diluted in two or three steps with pure N 2 in highpressure aluminum and nickel-coated manganese steel cylinders. To check the consistency between the HCl gas mixtures in the different cylinders, the HCl mixing ratios were analyzed by Fourier transform infrared spectroscopy. Four cylinders of 100 μmol mol −1 HCl gas mixtures agreed within 0.2 μmol mol −1 . A previous study showed that 0.29 μmol mol −1 of HCl was adsorbed on the inner surface of aluminum cylinders that contained 100 μmol mol −1 HCl gas mixtures. The long-term stability test showed that the 100 μmol mol −1 HCl gas mixture in the aluminum cylinder decreased by 0.8 μmol mol −1 over 2 years, whereas that in the nickel-coated manganese steel cylinder decreased by 6 μmol mol −1 . This result suggested that the nickel-coated manganese steel cylinder is not suitable for developing 100 μmol mol −1 HCl gas mixtures. From the verification test between gas cylinders and the long-term stability test, the 100 μmol mol −1 HCl standard gas mixture in the aluminum cylinder was successfully developed with an expanded uncertainty of 1.65 μmol mol −1 (k = 2%, 95% confidence level). The 100 μmol mol −1 HCl standard gas mixture was validated using an online ion chromatograph with a liquid Cl − certified reference material (CRM). The HCl gas mixture agreed with the liquid Cl − CRM within an expanded uncertainty of 1.5%.

Industrial stack gas emission measurements are important for process control, control of air pollution, and for implementing legislation regarding carbon dioxide emission rights. Measurements are typically performed using a range of process analysers for carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides (NOx), sulphur dioxide (SO2) and miscellaneous hydrocarbons. The calibration of these analysers is often performed using a series of binary mixtures of each component in nitrogen. For reasons of efficiency as well as a better match with true stack gas, the use of multi-component mixtures for this purpose would be preferred.The aim of this key comparison is to evaluate the measurement capabilities of national metrology institutes for carbon monoxide, carbon dioxide, nitrogen monoxide, sulphur dioxide and propane in nitrogen. Ten laboratories participated in the key comparison and one in the associated study. The key comparison reference value is based on the gravimetric preparation data.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).