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HS-GC determination of atmospheric greenhouse gases with direct in-vial sampling and multiple headspace extraction as
M J Cardador1, A Martín-Gómez1, J A Salatti-Dorado2
1Department of Analytical Chemistry, Chemical Institute for Energy and the Environment (IQUEMA), International Agri-Food Campus of Excellence (ceiA3), University of Cordoba, Spain.
Background:
Monitoring atmospheric greenhouse gases (GHGs) has become increasingly important due to growing interest in identifying emission sources and developing mitigation strategies. Reliable off-line measurements require robust analytical methodologies for sampling, preservation and analysis, capable of handling the wide concentration ranges encountered in environments with different emission levels. In this work, a headspace-gas chromatography method coupled to flame ionization and electron capture detectors (HS-GC-FID/ECD) has been developed and validated for the determination of CH4, CO2, and N2O in atmospheric air, introducing multiple headspace extraction (MHE) as a novel in-vial dilution strategy.
Results:
The method showed good linearity (R2 ≥ 0.99) within the ranges 0.74-15 ppmv for CH4, 25-2000 ppmv for CO2, and 0.03-0.75 ppmv for N2O. For samples exceeding these ranges, MHE was applied directly within the same vial to achieve controlled dilution, avoiding external gas handling or additional preparation steps. Sample stability was evaluated to support off-line analysis, demonstrating that crimp-sealed vials with PTFE-silicone septa stored at -20 °C preserve GHG concentrations for up to 5 days without significant losses. The method exhibits satisfactory precision and accuracy according to standard validation criteria. Its applicability was demonstrated by analyzing real air samples from urban and livestock environments, which were clearly differentiated by principal component analysis based on their GHG profiles.
Significance:
This study demonstrates, for the first time, the analytical potential of MHE as an effective in-vial dilution strategy for gaseous samples in GHG analysis. By enabling controlled dilution directly within the sampling vial, the approach extends the dynamic range of conventional headspace-GC measurements without external dilution systems or complex hardware. The method also supports direct in-vial sampling of atmospheric air and is fully compatible with automated headspace autosamplers, allowing streamlined workflows from field collection to instrumental analysis. Sample stability was evaluated for the specific vial-septum configuration to ensure reliable off-line measurements.
