Calibration of δ¹³C values of CO₂ gas with different concentrations in the analysis with laser absorption spectrometry

Stable carbon isotope ratio of carbon dioxide (δ¹³_CCO2) is used as an important indicator in the researches for global climate change and carbon capture and sequestration technology. The δ¹³C value has been usually analyzed with Isotope Ratio Mass Spectrometer (IRMS). Recently, the use of Laser Absorption Spectrometry (LAS) is increasing because of the cost efficiency and field applicability. The purpose of this study was to suggest practical procedures to prepare laboratory reference gases for δ¹³_CCO2 analysis using LAS. CO₂ gas was adjusted to have the concentrations within the analytical range. Then, the concentration of CO₂ was assessed in a lab approved by the Korea Laboratory Accreditation Scheme and the δ¹³_CCO value was measured by IRMS. When the instrument ran over 12 hours, the δ¹³C values were drifted up to ±10‰ if the concentration of CO₂ was shifted up to 1.0% of relative standard deviation. Therefore, periodical investigation of analytical suitability and correction should be conducted. Because δ¹³_CCO2 showed the dependency on CO₂ concentration, we suggested the equation for calibrating the concentration effect. After calibration, δ¹³_CCO2 was well matched with the result of IRMS within ±0.52‰.