Ultraviolet Spectral Analysis and Quantitative Detection of Heptafluoroisobutyronitrile (C₄F₇N) in a C₄F₇N–Carbon Dioxide (CO₂) Gas Mixture

Abstract

As an alternative to sulfur hexafluoride (SF₆) with great potential for application, heptafluoroisobutyronitrile-carbon dioxide (C₄F₇N-CO₂) gas mixture has been applied in various gas-insulated equipment. The insulation performance of the gas mixture is closely related to the mixing ratio. Therefore, accurate quantification of C₄F₇N in the C₄F₇N-CO₂ gas mixture has very important engineering significance. At present, there are few reports on the rapid quantitative detection of the concentration of C₄F₇N in the gas mixture. In this paper, a rapid analytical method for C₄F₇N concentration based on ultraviolet (UV) absorption spectroscopy is constructed. The UV spectral characteristics of C₄F₇N molecules are calculated by density functional theory. The appropriate bands that can be detected are determined by analyzing the calculated results. A concentration detection system of C₄F₇N based on UV absorption spectroscopy is built. Through analysis of the calculated results and experimental results, a quantitative detection method of C₄F₇N in the C₄F₇N/CO₂ gas mixture is determined. The method can achieve accurate detection of the concentration of the gas mixture in the conventional application range (including 4-10% C₄F₇N). The coefficient of the determination R² of the concentration inversion curve reaches 0.999 and the inversion error ratio does not exceed 5%. The related research results provide an important reference for the engineering application of the gas mixture.