Determination of CH4, CO2 and N2O in air samples and soil atmosphere by gas chromatography mass spectrometry, GC-MS

Abstract

A method for determination of the climate gases CH₄, CO₂ and N₂O in air samples and soil atmosphere was developed using GC-MS. The method uses straightforward gas chromatography (separation of the gases) with a mass spectrometric detector in single ion mode (specific determination). The gases were determined with high sensitivity and high sample throughput (18 samples h⁻¹). The LOD (3σ) for the gases were 0.10 µL L⁻¹ for CH₄, 20 µL L⁻¹ for CO₂ and 0.02 µL L⁻¹ for N₂O. The linear range (R² = 0.999) was up to 500 µL L⁻¹ for CH₄, 4000 µL L⁻¹ for CO₂ and 80 µL L⁻¹ for N₂O. The samples were collected in 10 mL vials and a 5 μL aliquot was injected on column. The method was tested against certified gas references, the analytical data gave an accuracy within ±5% and a precision of ±3%. The presence of ≤10% by volume of C₂H₂ (often used experimentally to prevent N₂ formation from N₂O) did not interfere with detection for the targeted trace gases.