High-Field Orbitrap Mass Spectrometry and Tandem Mass Spectrometry for Molecular Characterization of Asphaltenes

This work introduces a novel approach by use of high-energy collision-induced dissociation for fragmenting asphaltenes into their constituent stable aromatic cores as a means for determining the relative proportions of island-to-archipelago structures. This approach is particularly useful for comparing asphaltenes from various crude oils. Ion generation from asphaltenes was performed by use of atmospheric pressure photoionization, which has been demonstrated to provide hydrogen-to-carbon ratios consistent with bulk measurements by combustion analysis with less than 10% relative error. The fragmentation behavior of asphaltenes was first evaluated with model compounds consisting of island and archipelago structures by use of low- and high-energy collision-induced dissociation (CID and HCD). Unlike CID, HCD enables dissociation of model compounds to their stable aromatic cores. This allows facile classification as either island or archipelago on the basis of the discrepancy in the double-bond equivalents between the precursors and stable aromatic cores. Model compound studies also showed that when HCD is utilized for the simultaneous dissociation of multiple precursor ions, efficient fragmentation of all precursors only occurs when ions within a narrow mass window are presented for analysis. The HCD approach was then applied to characterize narrow mass segments of crude oil asphaltenes, including those derived from hydrotreated resids. Observed island-to-archipelago proportions were consistent with the chemical transformations that occur during the hydrotreating process. Importantly, the method also demonstrates that the proportion of island-to-archipelago structures in asphaltenes decreases with increase molecular weight.