Molecule of the Month
Tetracyclic Polyprenoids (TPPs) By Paul Farrimond
Two C30 tetracyclic polyprenoids (TPPs) are often seen as a characteristic doublet of peaks eluting after the C27-C29 diasteranes in the m/z 259 mass chromatogram from GC-MS analysis of oils and source rocks (Holba et al., 2000). Although often present in relatively low amounts, they are typically much more abundant in lacustrine oils and source rocks, and have attained prominence as one of the most useful indicators of these types of oils. Their origin is not known, but they are undoubtedly derived from precursor compounds in freshwater algae. Interestingly, related hexa- and heptacyclic polyprenoids have also been found in high abundance in certain lacustrine-sourced oils (e.g. Johnson et al., 2003; Farrimond et al., 2015), presumably from a similar origin.
A ratio of TPPs to some C26 steranes was devised by Holba et al., 2000), but this requires GC-MS-MS analysis. Simple examination of the prominence of the TPPs in the m/z 259 mass chromatogram relative to the steranes and hopanes in their chromatograms can give a good initial indication of their relative abundance, and thus whether or not the oil is likely to be lacustrine or not. Further analysis can then be done to confirm this.
References:
Farrimond P., Green, A. & Williams L. (2015). Petroleum geochemistry of the Sea Lion Field, North Falkland Basin. Petroleum Geoscience 21, 125-135.
Holba, A.G., Tegelaar, E., Singletary, M.S. & Albrecht, P. (2000). Tetracyclic polyprenoids: indicators of freshwater (lacustrine) algal input. Geology 28, 251-254.
Johnson, C.L. et al. (2003). Geochemical characteristics and correlation of oil and nonmarine source rocks from Mongolia. American Association of Petroleum Geologists Bulletin 87, 817-846.