Impurity Analysis of 5.5 N Nitrogen Gas and Its Impact on the Preparation of Class I Type Calibration Gas Mixtures

Knowledge of impurities in matrix gas is one of the critical requirements for the preparation of class I type calibration gas mixtures (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 % (5.5 N) as matrix gas. In this study, quantification of gaseous impurities such as moisture (H2O), methane (CH4), and carbon monoxide (CO) in 5.5 N nitrogen is performed using CRDS (cavity ring down spectroscopy). Carbon dioxide (CO2) and total hydrocarbons (THC) are analyzed using gas chromatography flame ionization detector (GC-FID), while the determination of nitrogen dioxide (NO2) impurity is conducted colorimetrically using a UV-Vis spectrophotometer. Total impurities in 5.5 N nitrogen are found to be (2945 +/- 21.5) ppb. The impact of utilizing this nitrogen is examined through the stability study of ambient range binary component gas mixtures of CH4 and CO in nitrogen and found that 5.5 N nitrogen can be used as matrix gas for preparing PRGMs of CH4 and CO. However, the component gas impurity present in nitrogen potentially affect the accuracy of gravimetrically prepared gas mixture.