Determination of carbon dioxide by gas chromatography using an electron capture detector for the analysis of greenhouse gases: A comparison and validation with the standard method

This study reports the development of a novel analytical method for the determination of carbon dioxide (CO₂) along with the other main greenhouse gases (GHG)‒methane (CH₄) and nitrous oxide (N₂O)‒ from environmental samples by gas chromatography (GC) using an electron capture detector (ECD). This new method was compared and validated with the standard GC method for the determination of CO₂ using a thermal conductivity detector (TCD). The main performance parameters considered for the validation of an analytical method were evaluated: selectivity/specificity, linearity/working range, precision, trueness, limit of detection (LOD) and limit of quantitation (LOQ). This comparison was carried out using gas standards, reference materials and environmental samples containing GHG. Both the ECD- and TCD-based chromatographic analytical methods displayed a similar precision (3.1-3.4 %) and accuracy (101-106 %) for CO₂ analysis. Although the LOQ for the ECD detector is higher than that of the TCD detector (300 vs. 99 µmol mol⁻¹), it is still sufficient for the analysis of most GHG samples. Once validated, the new analytical method was used for the simultaneous determination of CO₂, CH₄ and N₂O in gaseous samples obtained from a wide range of conditions and agricultural environments. To this end, a GC instrument was equipped with a flame ionization detector (FID) for the determination of CH₄ and an ECD for CO₂ and N₂O, connected in series by a system of valves. In this way, it was possible to accurately measure the main GHG present in the atmosphere and in gaseous samples, simplifying the required laboratory equipment and reducing the associated labor and costs.