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Accessing the reproducibility of sulfurized biomarkers in geological samples via Raney nickel treatment

Sulfurization,Raney nickel,Reproducibility,Biomarkers,Palaeoenvironmental reconstruction

Theme 1: Novel Tools and Techniques in Geobiology > Session 1e: Frontiers in Biomarkers and Application of Paleoecosystem Reconstruction

Abstract

        Organic molecules can undergo rapid reductive sulfurization with inorganic sulfur species, forming stable sulfurized biomarkers that cross-link into organic moieties¹. This process can obscure the original lipidome by sequestering native components into complex organic sulfur compounds, potentially biasing paleoenvironmental interpretations based solely on free lipids². Chemical desulfurization using mild reagents like Raney nickel has been widely employed in both modern and ancient systems³, liberating taxonomically informative hydrocarbons that are readily identifiable by gas chromatography and mass spectrometry. However, the application of Raney nickel in modern systems has been questioned due to observed anomalous increases in lipid production, which might be attributed to catalytic hydrogenation or hydrogenolysis⁴. While Raney nickel treatment appears promising for geological samples, its effectiveness has not been systematically evaluated. This study evaluates the reproducibility of biomarker release through Raney nickel treatment using a Tertiary oil sample from the Qaidam Basin. The reactions were carefully controlled with quantitative restrictions on both crude oil and Raney nickel catalyst. Parallel and gradient aliquots of reactants were prepared, and the resulting hydrocarbon products were analyzed using GC-FID and GC-QQQ-MS. The desulfurization process released a range of n-alkanes, steranes, hopanes, and carotenoids, distinct from the free hydrocarbon biomarkers. Biomarker ratios were determined and compared across parallel and gradient aliquots. The results demonstrate high reproducibility and comparability of the Raney nickel reaction, as evidenced by the stable biomarker ratios from desulfurized products from parallel aliquots. Notably, gradient aliquots exhibited a consistent trend in hydrocarbon product yields, indicating complete reaction and continuous release of sulfurized biomarkers with increasing reactant amounts. These findings suggest that sulfurized biomarkers in geological samples treated with Raney nickel are generally comparable. Furthermore, our results confirm that organic sulfur compounds in geological samples remain stably sequestered, preserving valuable paleoenvironmental information that can be reliably accessed through Raney nickel treatment.



References

1. Ma, J., Cui, X., Liu, X.L., Wakeham, S.G. and Summons, R.E., 2024. Rapid sulfurization obscures carotenoid distributions in modern euxinic environments. Geochimica et Cosmochimica Acta, 380, 180-193.


2. Kohnen, M.E.L., Sinninghe Damste, J.S. and De Leeuw, J.W., 1991. Biases from natural sulphurization in palaeoenvironmental reconstruction based on hydrocarbon biomarker distributions. Nature, 349(6312), 775-778.


3. Amrani, A., 2014. Organosulfur compounds: molecular and isotopic evolution from biota to oil and gas. Annual Review of Earth and Planetary Sciences, 42(1), 733-768.


4. Prahl, F.G., Pinto, L.A. and Sparrow, M.A., 1996. Phytane from chemolytic analysis of modern marine sediments: A product of desulfurization or not?. Geochimica et Cosmochimica Acta, 60(6), 1065-1073.