This key comparison was intended to compare the capabilities for the preparation and value assignment of gas standards for hydrogen sulfide in nitrogen, maintained at the participating national metrology institutes. The range of the nominal amount-of-substance fractions of the comparison standard is 10 µmol/mol, which is close to regulatory levels in most countries.

The measurements in this key comparison took place in 2005. There were 7 participants. The KCRV was calculated from the participants' data, and thus represents a consensus value. This was necessary due to the fact that the cylinders could not be prepared gravimetrically as hydrogen sulfide may be absorbed onto the walls of the cylinder, and has been shown to be unstable in cylinders at the comparison concentration. Thus the gas mixtures were procured from a vendor as a homogeneous lot of 12 cylinders, analyzed by the coordinating laboratory for 6 months to determine stability, and then those determined to be stable were shipped to the participants for analysis. After analysis, the cylinders were returned to the coordinating laboratory for reanalysis. Through this protocol the coordinating laboratory could track stability. In parallel, the coordinating laboratory also analyzed a stable reference, a hydrogen sulfide gas mixture that had been shown to be stable over many years. Using the lot stability data, the participant's analytical results, and the coordinating laboratories' analysis of the stable reference, a consensus value could be calculated which represents the concentration of the stable reference.

The key comparison demonstrated that the results of the laboratories agreed within 0.5% relative to the consensus value. A subset of 6 participants' results agreed with the consensus value to better than 0.25%.

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).