Deciphering the binding strength of oil matrix through molecularly resolved release energy analysis using thermal slicing ramped pyrolysis GC-MS.

Recent advancements in analytical techniques have significantly furthered our understanding of the chemical composition of petroleum and its derivatives. However, there remains a missing link connecting the molecular structure with how specific compounds are bound within the sample matrix. Traditional approaches to study energetic characteristics of petroleum often rely on bulk property measurements (e.g., thermogravimetric analysis), therefore lacking the resolution needed to capture compound-specific interactions and structural information. In this work, we aim to fill the gap between compositional and energetic analyses by employing thermal slicing ramped pyrolysis gas chromatography mass spectrometry (TSRP-GC-MS). TSRP-GC-MS enables the analysis of temperature-dependent release patterns of pyrolyzates, linking molecular structures to energetic characteristics via computing the energy distributions for specific pyrolyzates. Results of the photodegradation experiments demonstrate that as the photodegradation proceeds, the energy required to disrupt the matrix and to release n-alkanes increased from ca. 90 kJ/mol to over 100 kJ/mol, with significant increases for each individual n-alkane. The release energy of individual n-alkanes in crude oil and in tarball collected in the field were further compared in the second case study. The results not only showed an increase from 110 kJ/mol for n-alkanes in crude oil to 118 kJ/mol in tarball, but also revealed a homogenizing trend of the matrix strength of different n-alkanes in the latter. Overall, the proposed TSRP-GC-MS approach offers a powerful tool for advancing our understanding of petroleum and oil and has the potential to be expanded to the study of other complex natural mixtures.