Quality assurance of carbon dioxide gas by gas chromatography- mass spectrometry for nuclear applications

Carbon dioxide (CO₂) due to its low thermal conductivity and low chemical reactivity is used as an annulus gas in pressurized heavy water reactors (PHWR) for monitoring the leak of heavy water from pressure tube or calandria. CO₂, however, can contain such impurities as free chloride, vinyl chloride and polyaromatic hydrocarbons as which can induce corrosion of the structural material. Therefore, it is desirable to determine the contents of these impurities with good precision and accuracy. The present communication describes a gas chromatography- mass spectrometry (GC-MS) based methodology for the sensitive and precise measurement of vinyl chloride in CO₂. The analysis consists of three steps in the following order: pre-concentration by solid phase extraction; quantitative elution and finally determination by GCMS. In this work, 2.52 L of CO₂ gas at NTP (300K) was passed through activated charcoal cartridge, where vinyl chloride was adsorbed. Then the analyte was extracted using 2 mL of methanol. The extracted eluent (1uL) was then injected into GC for vinyl chloride analysis. Concentration of the analyte was calculated against the calibration plot of the standard compound, The concentration of vinyl chloride was found to be in the range of; 0.005248 to 0.092 μL/L in different samples of CO₂ gas analysed. (author)