5 years ago

Single Dalton Collision-Induced Dissociation for Petroleum Structure Characterization

Single Dalton Collision-Induced Dissociation for Petroleum Structure Characterization
Kuangnan Qian, Michael R. Harper, Thomas R. Fredriksen, Amy C. Clingenpeel, Ashley M. Wittrig
Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been used to assign elemental formulas to tens of thousands of ions generated from petroleum samples. While elemental formulas can give insights on hydrogen deficiency or heteroatom content, they do not directly give structural information. Previous broadband collision-induced dissociation (CID) experiments yielded useful information on the aromatic cores of petroleum molecules. However, it is difficult to track parent-product correlations in broadband experiments. In this work, isomers and isobars in a single dalton window were isolated and subjected to CID to obtain more conclusive information on the core structures of the ions. Several aromatic ring class fractions of a heptane deasphalted vacuum residue (VR) and the associated asphaltene fraction were examined by CID mass spectrometry. A 15T FT-ICR mass spectrometer was used with atmospheric pressure photoionization to probe the structural features of each fraction. Ions that differ in mass by n*14 Da (or n*CH2 units) were selected for isolation to screen for differences within the same homologous series across the mass range of the sample. Each packet of ions was isolated and fragmented to reveal aromatic cores with some fragment ions retaining alkyl chains. The assigned molecular formulas from ultrahigh resolution MS combined with the structural information suggested by the liquid chromatography (LC) separation enabled greater confidence in proposed parent ion structures. In the measurements performed, single core and multicore fragment ions were observed for the deasphalted aromatic fractions whereas the asphaltene fraction produced primarily single core fragment ions.

Publisher URL: http://dx.doi.org/10.1021/acs.energyfuels.7b02478

DOI: 10.1021/acs.energyfuels.7b02478

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