A Case Study on Impurity analysis of 5.5N Nitrogen gas and its impact on the preparation of Primary Reference Gas MixturesAuthor(s): Daya Soni
Knowledge of impurities in matrix gas is one of the critical requirements for the preparation of Primary Reference Gas Mixtures (PRGMs) as per ISO 6142-1. PRGMs are prepared gravimetrically using high-purity component gas and high-grade nitrogen, here 99.9995% (5.5N) as matrix gas. In this paper, gaseous impurities such as moisture (H2O), methane (CH4), and carbon monoxide (CO) in 5.5N nitrogen are quantified using CRDS (cavity ring down spectroscopy), carbon dioxide (CO2), total hydrocarbons (THC) are analyzed using gas chromatography flame ionization detector (GC-FID) and nitrogen dioxide (NO2) impurity determined colorimetrically using UV-Vis spectrophotometer. Total impurities for 5.5N nitrogen are found to be (2945 ± 21.5) ppb. The impact of using this nitrogen is examined from the stability study of ambient range binary component gas mixtures of CH4 and CO in nitrogen and found that 5.5N nitrogen can be used as matrix gas for preparing PRGMs of CH4 and CO but the component gas impurity present in nitrogen can affect the accuracy of gravimetrically prepared gas mixture.