Alkane extraction from rock

Molecular fossils have been successfully identified in younger Precambrian rocks and linked to certain classes of biological source material. In organic analyses of ancient sediments the cleaned, pulverized rocks are treated with organic solvents to extract a soluble fraction containing the less complex and more easily identifiable compounds. However, this fraction is more subject to contamination since it is not locked within the rock matrix. Normal alkanes have been identified in extracts of the 3 billion year old Fig Tree Shale. These alkanes have a probable biological origin in cellular lipids. The odd and even-numbered alkanes are evenly distributed, a characteristic of alkanes from ancient rocks. It is uncertain, however, whether these compounds were present at the time of deposition or derived from a later source [24]. 

Levy et al. [392] briefly investigated alternative fluids for on-line SFE-capil-lary GC with C02, N20, and SF6 for the extraction of PAHs and alkanes from solid waste, sediment, and shale rock. They initially compared the extraction efficiency of pure fluids and then some fluid mixtures. They found that 20% SF6 in C02 was more effective at 375 bar, and 50 °C for 30 min than each pure fluid for removing both PAHs and alkanes. 

Geochemists and the oil industry routinely screen rock samples for bio-markers that indicate the age and source of hydrocarbon constituents. The conventional extraction takes 48 hours and requires extract clean-up by thin-layer chromatography to separate the alkanes from aromatic hydrocarbons and heteroatom containing species (16). Here the selectivity of SFE in extracting only the alkanes from a mature source rock... 

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