Final report on international key comparison CCQM-K53: Oxygen in nitrogen

• Published in: Metrologia 2010-01, p.1
• Main Authors: Lee, Jeongsoon, Lee, Jin Bok, Moon, Dong Min, Kim, Jin Seog, van der Veen, Adriaan M H, Besley, Laurie, Heine, Hans-Joachim, Martin, Belén, Konopelko, L A, Kato, Kenji, Shimosaka, Takuya, Castorena, Alejandro Perez, Macé, Tatiana, Milton, Martin J T, Kelley, Mike, Guenther, Franklin, Botha, Angelique
• Format: Article
• Language: English
• Subjects: Agreements; Comparative analysis; Coordination; Gases; Measurement techniques; Nitrogen; Oxygen; Standard deviation
• ISSN: 0026-1394; 1681-7575

Gravimetry is used as the primary method for the preparation of primary standard gas mixtures in most national metrology institutes, and it requires the combined abilities of purity assessment, weighing technique and analytical skills. At the CCQM GAWG meeting in October 2005, it was agreed that KRISS should coordinate a key comparison, CCQM-K53, on the gravimetric preparation of gas, at a level of 100 ...mol/mol of oxygen in nitrogen. KRISS compared the gravimetric value of each cylinder with an analytical instrument. A preparation for oxygen gas standard mixture requires particular care to be accurate, because oxygen is a major component of the atmosphere. Key issues for this comparison are related to (1) the gravimetric technique which needs at least two steps for dilution, (2) oxygen impurity in nitrogen, and (3) argon impurity in nitrogen. The key comparison reference value is obtained from the linear regression line (with origin) of a selected set of participants. The KCRV subset, except one, agree with each other. The standard deviation of the x-residuals of this group (which consists of NMIJ, VSL, NIST, NPL, BAM, KRISS and CENAM) is 0.056 ...mol/mol and consistent with the uncertainties given to their standard mixtures. The standard deviation of the residuals of all participating laboratory is 0.182 ...mol/mol. With respect to impurity analysis, overall argon amounts of the cylinders are in the region of about 3 ...mol/mol; however; four cylinders showed an argon amount fraction over 10 ...mol/mol. Two of these are inconsistent with the KCRV subset. The explicit separation between two peaks of oxygen and argon in the GC chromatogram is essential to maintain analytical capability. Additionally oxygen impurity analysis in nitrogen is indispensable to ensure the preparative capability. (ProQuest: ... denotes formulae/symbols omitted.)