Development of nitrogen and oxygen certified reference materials in 10 mu mol/mol for the purity evaluation

We have developed 10 mu mol/mol nitrogen and oxygen certified reference materials (CRMs) in helium, as a SI-traceable gas standard for a quantifying of impurities in pure gases for the first time in Korea. The standard gas mixtures of nitrogen and oxygen were prepared in 5000 mu mol/mol and sequentially were diluted to 250 mu mol/mol and 10 mu mol/mol according to the gravimetric preparation. In each dilution step, two cylinders of CRMs were prepared. The verification of internal consistency among the prepared gas mixtures was performed by using GC-TCD. The amount fractions and those expanded uncertainties (k= 2) of nitrogen and oxygen in the standard gas mixtures were (10.12 +/- 0.08) mu mol/mol and (10.18 +/- 0.08) mu mol/mol for nitrogen, and (9.88 +/- 0.06) mu mol/mol and (9.94 +/- 0.06) mu mol/mol for oxygen, respectively. We have conducted a purity assessment of two commercial helium gases using developed CRMs. As the results of the purity assessment, nitrogen and oxygen were detected by (1.66 +/- 0.03) mu mol/mol and (0.31 +/- 0.02) mu mol/mol, respectively, as the impurities in one of the pure helium.