International key comparison APMP.QM-S1: Comparison of primary standards of nitrogen in helium

Abstract

Gravimetry has been used as the primary method for the preparation of primary standard gas mixtures in most NMIs. In the uncertainty evaluation of primary standard gas mixtures, the purity analysis and the weighing of gases are very important. In general key comparisons, the uncertainty of analysis is bigger than that of preparation, and accurate comparison about the capability of preparation of primary standard gas mixtures is significantly difficult.In this comparison, the concentration of nitrogen has been chosen as that which can easily be analyzed using GC-TCD with small uncertainty and weighed in almost the same range for component and balance gases.Participants sent a primary standard gas mixture composed of about 12.5% mol/mol nitrogen in helium to the coordinating laboratory with the report of the purity analysis and the gravimetric preparation including raw data. The coordinating laboratory analysed each standard gas cylinder with GC-TCD and compared with reported concentration values.From the results, it was clear that there were no outliers in this comparison. Consequently, the distribution of the results is regarded as a normal distribution and an arithmetic mean was used as the reference value. The results were then analysed in terms of degrees of equivalence.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 APMP, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).