A pyrolysis and stable isotopic approach to investigate the origin of methyltrimethyltridecylchromans (MTTCs)

Methyltrimethyltridecylchromans (MTTCs) have been widely detected in sediments and crude oils from various depositional settings and are established markers for palaeosalinities. A likely origin of these compounds, which show a distinctive isoprenoid substituted aromatic structure, seems to be condensation reactions of phytol with higher plant derived alkyl phenols during early diagenesis. However, a direct biological origin from phytoplanktonic organisms cannot be excluded. To further investigate the potential origin from condensation reactions, an online pyrolysis–gas chromatography–isotope ratio mass spectrometry (PY–GC–irMS) method with the capacity to measure δ13C in fragments (trimethylphenol and pristenes) generated from 5,7,8-trimethyl-MTTC was developed in this study. This straight forward technique poses a great potential for the elucidation of chroman formation in geological samples as it possibly enables the distinction between the different proposed sources of isoprenoid and alkyl-phenol fragments (mainly phytoplankton and higher plants, respectively) based on their stable isotopic compositions. Furthermore, it might be useful for the investigation of products generated from MTTCs during thermal maturation of geological samples.