New Application of Solid-phase Microextraction (SPME) in Analyzing Volatile Hydrocarbons (C1–C9) in Natural Gas

Solid-phase microextraction (SPME) coupled with gas chromatography-isotope ratio mass
spectrometry (GC-IRMS) has already been applied to collect and identify volatile light hydrocarbons in
oil and source rocks. However, this technology has not yet been used to analyze volatile light
hydrocarbons in dry gas (natural gas with C1/C2+>95%). In this study, we developed a method to
measure the molecular and carbon isotope composition of natural gas using Divinylbenzene/
Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS) fiber. This fiber proved to be suitable for extracting
C1–C9 hydrocarbons from natural gas without inducing carbon isotopic fractionation. Notably, the
extraction coefficients of the analytes were not the same, but rather increased with the increasing
carbon number of the hydrocarbons. Nevertheless, we successfully identified 24 hydrocarbons from
the in-lab standard natural gas, while also obtaining the carbon isotope composition of C1 to C9
hydrocarbons with satisfying repeatability. The relative standard deviation (RSD) of the molecular
composition data was in the range of 0.06–0.74%, with the RSD of the carbon isotope composition
data not exceeding 1‰. Finally, seven natural gas samples, collected from different sedimentary
basins, were successfully analyzed and the stable carbon isotope compositions of C1–C9
hydrocarbons present in these were determined through this method.