Abstract
Sample preparation technique, for the analysis of δ13C ratios in oil and gas samples, has gradually been recognized as one of the most crucial steps of the whole analytical process. In this study, a new convenient method, syringe solid phase extraction (SSPE), was proposed for measuring δ13C in natural gas samples. Based on conditional experiments of temperature and time, SSPE fitted with activated carbon adsorbent was applied with a gas chromatography/isotope ratio mass spectrometry (GC/IRMS) system for trace carbon isotope analysis. The results showed that isotopic fractionation was not clearly observed during the adsorption and desorption process, and the δ13C ratios measured by SSPE-GC/IRMS were in good agreement with the known δ13C ratios of CH4~C5H12 measured by GC/IRMS with the accuracy all within ±0.48‰. A natural gas sample was applied to verify the efficiency of this new method, and the obtained results confirmed that SSPE-GC/IRMS is a reliable technique characterized with simplicity, efficiency, and reliability.
Highlights
Compound-specific isotope analysis (CSIA) features with a gas chromatograph (GC) interfaced to an isotope ratio mass spectrometry (IRMS) are a reliable sample pretreatment tool for normal level carbon isotope analysis of hydrocarbons in environmental forensics, archaeology, ecology, and gas geochemistry [1,2,3,4,5,6,7,8,9,10,11]
The δ13C ratios of CH4 were comprised between -42.7 and -41.1‰, C2H6 was distributed from -30.4 to -28.4‰, C3H8 was clustered between -28.3 and -27.0‰, i-C4H10 was ranged from -27.4 to -25.7‰, n-C4H10 was clustered between -27.1 and -26.0‰, i-C5H12 was located in the range of -25~23.6‰, and n-C5H12 ratios were ranged from -25.1 to -22.8‰
The syringe solid phase extraction (SSPE)-gas chromatography/isotope ratio mass spectrometry (GC/IRMS) technique based on solid phase microextraction (SPME)-GC/IRMS was conducted on standard and geological samples with different adsorbents, temperatures, and times to determine the optimized experimental condition and achieve the analyzed trace hydrocarbon isotope
Summary
Compound-specific isotope analysis (CSIA) features with a gas chromatograph (GC) interfaced to an isotope ratio mass spectrometry (IRMS) are a reliable sample pretreatment tool for normal level carbon isotope analysis of hydrocarbons in environmental forensics, archaeology, ecology, and gas geochemistry [1,2,3,4,5,6,7,8,9,10,11]. Geofluids have been carried out, and some novel and practical methods such as purge and trap (P&T) and solid phase microextraction (SPME) have been put forward, and these highly efficient techniques made remarkable achievements for preconcentration of trace volatile or semivolatile organic compounds [21,22,23,24,25]. Though these works greatly improved the detection limit for most trace compounds, these often exhibited selectivity for some hydrocarbon compounds during the extraction process, making the whole analysis quite unfeasible. With the consideration of fractionation, the integrated study of time and temperature during the adsorption and desorption process is carried out to determine the optimized experimental condition
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