“To assess the variability of gas compositions, several dominating compounds were selected based on previous research (Fabiańska et al. 2013). Molecular compositions of self-heating gases (CH4, C2H6, C3H8, iC4H10, nC4H10, C5H12, C6H14, C7H16, unsaturated hydrocarbons, CO2, O2, H2, N2) were determined on an Agilent 7890A gas chromatograph equipped with a set of columns, and flame ionization (FID) and thermal conductivity (TCD) detectors. This GC is configured to do an extended natural gas analysis up to C14. The analyzer is a three-valve system using three 1/8-inch packed columns (3 ft Hayesep Q 80/100 mesh, 6 ft Hayesep Q 80/100 mesh, and 10 ft molecular sieve 13 × 45/60 mesh) and a GS-Alumina capillary column (50 m × 0.53 mm). The system consists of two independent channels. The channel using the FID for the detailed hydrocarbon analysis is a simple gas sampling valve injecting the sample into the GS-Alumina column. The second channel using packed columns is for determination of methane, ethane, and non-hydrocarbon gases. The GC oven was programmed as follows: initial T of 60 °C held for 1 min., then to 90 °C at 10 °C/min., then to 190 °C at 20 °C/min., and finally held for 5 min. The front detector (TCD) was operated at 150 °C, and the back detector (FID) at 250 °C. Helium was used as a carrier gas flowing through the TCD channel at cm3 min−1 and through the FID channel at cm3 min−1.”
