Abstract

A Case Study on Impurity analysis of 5.5N Nitrogen gas and its impact on the preparation of Primary Reference Gas Mixtures

Author(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.