Over the past 20 years, advances in modern high resolution / ultra-high resolution mass spectrometry have forever changed the expectations of complex mixture analysis. Aided by advances in ionization methodologies that facilitate the molecular-level analysis of high boiling/polar species, ultra-high resolution mass spectrometry routinely resolves and identifies (at the level of elemental composition assignment), tens-of-thousands of species that comprise each of the acidic, basic, aromatic, and aliphatic components of petroleum samples. These analytical capabilities have been used to revisit, and ultimately support a decades old theory of the composition of petroleum (the Boduszynski Continuum) and expose the compositional constraints (in class, type, and carbon number) imposed by boiling point. Such compositional information, combined with knowledge of the Boduszynski Continuum, is now poised to push forward to the molecular-level modeling of heavy ends (Petroleomics). However, asphaltene characterization is an important part of these efforts.<br/>Asphaltenes have long been the subject of intense debate, but modern analytical techniques have recently brought clarity to a number of the most important issues. First, asphaltene average molecular weight is in the 500-1000 Da range with a complete distribution that can span 300 – 3000 Da, which is sample dependent. Next, despite overwhelming literature support to the contrary, asphaltenes are comprised of abundant island and archipelago structural motifs, and the dominant form is also sample dependent. Lastly, the mass spectral support for the island model is due to selective ionization. Simply, island asphaltenes ionize ~50-fold more efficiently than archipelago structures. Without their removal prior to mass spectral analysis, even asphaltenes that are archipelago-dominant will be incorrectly identified as island-dominant. Separation strategies designed to selectively remove islandic structures have revealed abundant archipelago-dominant fractions that can comprise as much as 70+ weight percent of the sample. Here, we review our efforts over the past 16+ years in the mass spectral characterization of asphaltenes and note the important discoveries that have led us to our current understanding of asphaltene structure.

Asphaltenes are comprised of abundant island and archipelago structural motifs: A mass spec lesson in selective ionization

255th National Meeting (2018)

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