International comparison CCQM-K46: Ammonia in nitrogen

Abstract

Ammonia is an important compound in the chemical industry. It is widely used and is the basis for producing other compounds containing nitrogen. Ammonia is also very hazardous, and consequently emissions of ammonia need be controlled and monitored. In the past years, several national metrology institutes have developed facilities for the preparation of Primary Standard gas Mixtures (PSMs), dynamically generated ammonia mixtures and facilities for comparing and certifying gas mixtures containing ammonia.The amount-of-substance fraction level of ammonia chosen for this key comparison is 30–50 µmol/mol. The results of this key comparison revealed that there is at present no consensus among static and dynamic techniques for gas mixture preparation for this component in this range. As key comparison reference value (KCRV), the mean of the three methods is used. In its uncertainty, no allowance is made for the observed biases. With respect to the KCRV, only two laboratories report consistent results. When grouped in accordance with the employed methods, the results are consistent. Further experimental work is needed.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).

Metrology for ammonia in ambient air – concept and first results of the EMRP project MetNH3

“…The efforts of the gas metrology community to tackle these issues are aptly summarised in the report of the international key comparison CCQM-K46 [2]. In this comparison exercise, mixtures with nominal amount fraction over the range of 30-50 μmol/mol were distributed to the participating NMIs, who in turn certified these mixtures using their own in-house reference standards and methods.…”

“…Furthermore, the highly adsorptive properties of gas-phase ammonia raise difficulties in the construction of sampling inlets for analyzers, as well as for the preparation of reference gas mixtures. Inter-comparison experiments have shown significant discrepancies between different measurement methods [1], and the agreement even between reference materials provided by European National Metrology Institutes (NMIs) is unsatisfactory [2].…”

CCQM_retrospectoscope reference manual:

“…Note: The dataset, International Comparison CCQM-K46 -Ammonia in Nitrogen [17], was chosen as the example because (unusually for CCQM studies) the results turned out to be method-dependent. The discordance between the methods facilitates display of optional chart elements.…”

Dilution and permeation standards for the generation of NO, NO2and SO2calibration gas mixtures

“…Gas mixtures standards in ordinary pressurized cylinders of the concerned reactive pollutants, especially of NO 2 , are known to have reduced stabilities at low amount fractions. Absorption, residual impurities and catalysed reactions of the analytes at the recipient's surface, in pressure regulators or in the remaining gas manifold are named reasons [6,7]. Dedicated reference laboratories have therefore developed traceable in situ generation methods (calibrators) based on dynamic methods.…”