Computerised gas chromatographic—mass spectrometric and high-performance liquid chromatographic analysis of sedimentary benzoporphyrins

Recently developed gas chromatographic—mass spectrometric (GC-MS) and high-performance liquid chromatographic (HPLC) procedures for the analysis of petroporphyrios have been employed in the search for benzoporphyrins in six sediments, a bitumen and a petroleum. In addition, structurally assigned monobenzocycloalkanoporphyrms (benzo-CAPs) isolated from Boscan crude oil (Cretaceous, Venezuela) have been used in a co-chromatographic study of these minor components (ca. 1% of total porphyrins). The petroporphyrins are generally obtained by demetallation of metalloporphyrins from samples representing a variety of geographical locations and ages ranging from Permian (ca. 235 million years) to Palaeocene (ca. 60 million years). The data show that, where the benzo-CAPs were detected, up to 24 components can occur, although the dominant member in each case is the C33 compound. Studies of a chromatographic fraction from Boscan crude oil, enriched in high-carbon-number benzo-CAPs, indicates that the series extends from at least C30 to C38 in this sample. The GC behaviour of the benzo-CAPs as the bis(tert.-butyldimethylsiloxy)Si(IV) [(TBDMSO)2Si(IV)] derivatives is characterised by the high Kovats retention indices (ca. 3900-4300; OV-1 column). Similarly, under normal-phase HPLC conditions, the free-base benzo-CAPs elute after the major alkylporphyrins. HPLC co-chromatography of the free-bases provides a rapid means of identification of the major benzo-CAPs (C32 and C33), while the GC-MS procedure allows more detailed characterisation and quantitation of the benzo-CAP distributions as their (TBDMSO)2Si(IV) derivatives.