Structural investigations of Monterey kerogen by sequential chemical degradation

Two successive degradation steps involving Na 2 Cr 2 O 7 /AcOH and RuO 4 were carried out on a Type II-S kerogen from the Miocene Monterey Formation (California) after pre-saponification of the ester bonds by KOH/MeOH treatment. Detailed gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS) analysis of the soluble acids revealed significant qualitative and quantitative variation of the various types of products obtained from the two different degradation steps. Maleimides (lH-pyrrole-2,5-diones), dominated by Me,Et-maleimide, were the major degradation products released by Na 2 Cr 2 O 7 /AcOH oxidation indicating that their precursors, probably tetrapyrrole pigments, occur ether- as well as sulfur-bound in the kerogen. On the other hand, a scarcely reported homologous series of 2-methyl- n -alkanoic acids (C 8 –C 27 ) was identified as the most prominent series of carboxylic acids obtained after RuO 4 oxidation. The results support the high specificity of the RuO 4 oxidation method in revealing information on the nature of the alkyl chains substituting the aromatic moieties in the kerogen structure and point to the presence of aryl–alkyl ether groups in the kerogen. The significance of the lipid composition of the kerogen is further discussed in terms of biomarker information and their original attachment to the macromolecular structure.