Application Note

Analysis Of Molecular Fossils: Crude Oil Steroid Biomarker Characterization Using Triple Quadrupole GC-MS/MS

Source: Thermo Scientific Brand Products, Part of Thermo Fisher

Due to the variety of geological conditions and ages under which oil was formed, every crude oil exhibits a unique biomarker fingerprint. Because of this, biological biomarkers are the most important hydrocarbon groups in petroleum because they can be used for chemical fingerprinting. Biomarkers reveal all or most of the original carbon skeleton of the original natural products. Relative to other hydrocarbon components petroleum biomarkers are more resistant to biodegradation but concentrations steadily decrease as petroleum matures. The information from biomarker analysis is used to determine the migration pathways from a source rock to the reservoir, for the correlation of oils in terms of oil-to-oil and oil-to-source rock, the source potential, ranking of the relative thermal maturity, as well as possible secondary alteration processes. Decisions for the commercial exploitation of a prospect are based on that analytical background. Economics ultimately determine if a petroleum reservoir is further developed and finally brought to the market. Refinery chemists are mostly interested in how oil behaves when feeding the processes into marketable products. Analyses of petrochemical biomarkers also have been proven useful in the determination of petroleum-derived environmental contaminations.

Biomarkers found in crude oils, rocks and sediments, also referenced as “molecular fossils” in the literature, demonstrate few or even no changes from their former precursor compounds: terpenoids (isoprenoids) and steroids found in the cells of the originating living organisms. Biomarker concentrations in oils are low, typically in the low ppm and sub-ppm level in the presence of a highly complex petroleum hydrocarbon matrix. As the concentrations of biomarkers in petroleum decrease with thermal maturity, oils of high maturity exhibit particular analytical challenges with only low biomarker concentrations. Highly selective, fast and sensitive mass analyzers as high resolution or triple quadrupole GC/MS instruments are common and required for meaningful biomarker analysis.

Triple quadrupole mass spectrometry allows the determination of the structure related precursor-product ion relationships with significantly less matrix interference than single stage quadrupole MS. Based on the selected reaction monitoring process (SRM) triple quadrupole technique provides a unique selectivity for biomarker studies. The analysis of sterane, tricyclic and pentacyclic terpanes (hopanes) biomarker have been subject to the described application.