Speciation and δ34S analysis of volatile organic compounds in crude oil by GC-MC-ICP-MS using the Thermo Scientific GCI 300 Interface

Importance of the Topic

The isotopic composition of sulfur in organic compounds provides critical insight into the geological origin and alteration history of crude oil. Compound‐specific δ34S analysis can reveal redox processes such as thermochemical sulfate reduction in paleo‐environments and support petroleum exploration, quality control, and environmental forensics.

Aims and Study Overview

This study demonstrates the coupling of a Thermo Scientific Trace 1310 GC to a Neptune Plus MC-ICP-MS via the GCI 300 Interface to measure δ34S values of individual volatile sulfur species in diverse crude oil samples. Four oils (Bryan Mount, Basrah Light, Saudi Light, Saudi Medium) were profiled to assess instrument performance, reproducibility, and the ability to fingerprint source and alteration processes.

Methodology and Instrumentation

Samples were prepared at 1:200 dilution in hexane with 3-hexylthiophene as an internal standard. After filtration, 1 µL injections were separated on a 30 m × 0.25 mm × 0.25 µm GC column under a temperature ramp (100 °C to 300 °C). The GCI 300 Interface maintained a homogeneous transfer line at 195 °C and allowed SF6 addition for plasma tuning. The Neptune Plus was operated at medium resolution (Δm/m ≈ 5 000), 1.2 kW RF power, and Ar carrier flow. A linear drift correction based on signal slope was applied to each chromatographic peak.

Used Instrumentation

• Thermo Scientific Trace 1310 Gas Chromatograph
• GCI 300 Interface with semi-demountable torch and T-insert
• Thermo Scientific Neptune Plus Multicollector ICP-MS
• Thermo Scientific EA IsoLink IRMS (reference δ34S calibration)

Main Results and Discussion

Eleven major sulfur‐containing peaks were resolved in all oils. Dibenzothiophene was the only compound unambiguously identified by retention time versus standards; adjacent peaks were inferred as benzothiophenes or alkylated derivatives. Average δ34S shifts of 2–3 ‰ between benzothiophenes and dibenzothiophenes were consistent across samples, indicating limited thermochemical sulfate reduction. Individual peaks in Saudi Light showed up to 5 ‰ variation, reflecting molecular structure effects. The δ34S signature of dibenzothiophene distinguished each crude oil source.

Benefits and Practical Applications

GC-MC-ICP-MS with the GCI 300 Interface delivers compound‐specific δ34S with high reproducibility and resolution. It enables forensic fingerprinting of crude oils, tracking alteration pathways, and supporting QA/QC in refinery streams. The method requires minimal sample, offers non‐destructive speciation, and integrates seamlessly with existing GC workflows.

Future Trends and Possibilities

Advances in data processing automation and real-time drift correction will further improve precision. Expanding the technique to heavier sulfur compounds, heteroatom classes, and coupling with two‐dimensional GC could deepen insights into complex mixtures. Integration with environmental monitoring and reservoir management may broaden applications beyond petroleum geochemistry.

Conclusion

The GCI 300 Interface coupled GC-MC-ICP-MS provides reliable δ34S speciation of volatile sulfur compounds in crude oil. The platform offers robust isotopic fingerprints for source identification and paleoenvironmental reconstruction, highlighting its value in analytical geochemistry and industrial applications.

References

• Seal, R. R. Review in Mineralogy & Geochemistry 2006, 61, 633–677.
• Amrani, A.; Sessions, A. L.; Adkins, J. F. Analytical Chemistry 2009, 81, 9027–9034.
• Li, S.; Amrani, A.; Pang, X.; Yang, H.; Said-Ahmad, W.; Zhang, B.; Pang, Q. Organic Geochemistry 2015, 78, 1–22.
• Gvirtzman, Z.; Said-Ahmad, W.; Ellis, G. S.; Hill, R. J.; Moldowan, J. M.; Wei, Z.; Amrani, A. Geochimica et Cosmochimica Acta 2015, 167, 144–161.
• Greenwood, P. F.; Amrani, A.; Sessions, A.; Raven, M. R.; Holman, A.; Dror, G.; Grice, K.; McCulloch, M. T.; Adkins, J. F. In Principles and Practice of Analytical Techniques in Geosciences; Royal Society of Chemistry, 2015; pp. 285–312.
• Krupp, E. M.; Donard, O. F. X. International Journal of Mass Spectrometry 2005, 242, 233–242.
• Hirata, T.; Hayano, Y.; Ohno, T. Journal of Analytical Atomic Spectrometry 2003, 18, 1283.
• Kimura, J.-I.; Chang, Q.; Kanazawa, N.; Sasaki, S.; Vaglarov, B. S. Journal of Analytical Atomic Spectrometry 2016, 31, 790–800.
• von Quadt, A.; Wotzlaw, J.-F.; Buret, Y.; Large, S. J. E.; Peytcheva, I.; Trinquier, A. Journal of Analytical Atomic Spectrometry 2016, 31, 658–665.