The analysis of polar fractions from sediment extracts and crude oils using reaction-gas chromatography–mass spectrometry

Reaction-gas chromatography–mass spectrometry (R-GC–MS) has been used to analyse the polar fractions of sediment extracts and crude oils. Functionalised species were hydrogenolysed in the presence of hydrogen carrier gas, over a palladium black catalyst contained within the vapourising injector of a gas chromatograph-mass spectrometer. Model compound studies showed that the fully active catalyst was effective in hydrogenating and isomerising alkenes, partially hydrogenating aromatic moieties and desulfurising thiols, sulfides, and thiophenes. Primary alcohols, acids, esters and ethers were defunctionalised to produce hydrocarbons with one carbon atom fewer than the reactant, while secondary alcohols were reduced to the parent hydrocarbon. The R-GC–MS analysis of the polar fractions of the Heartbreak Ridge lignite (Bremer Basin, Western Australia; Eocene age) and the Monterey Formation shale (Naples Beach, USA; Miocene age) extracts produced biomarker hydrocarbons which had lost their biological stereochemistry, but nonetheless reflected organic matter sources. In contrast, R-GC–MS analysis of the polar fractions from Exxon Program crude oils released lesser amounts of very similar, non-specific hydrocarbons. Thus the majority of the components of thermally mature polar fractions, as well as asphaltenes, do not react under the selected R-GC–MS conditions. Although less specific than traditional chemical degradation techniques, R-GC–MS affords a rapid and detailed molecular analysis of small quantities of sample that will be of particular use for characterising immature complex polar mixtures.