The chemical description of heavy petroleum fractions remains problematic and motivates instrumental developments. In this respect, particularly high-resolution mass spectrometry has proven to be a powerful approach. Direct infusion approaches remain the most widely used concept but isomeric specification is not easily feasible. Ion mobility coupled to high-performance mass spectrometry allows for an additional structural dimension but the devices are still limited in ion mobility and mass spectrometric resolving power. To overcome these limitations, we explored the capabilities of cyclic ion mobility high-resolution mass spectrometry with special emphasis on petrochemical applications. The unique architecture of the instrument allowed a building block experimental design. Simply increasing the pass number in the cyclic ion mobility separation device (cIMS) was not feasible due to fast compact ions surpassing the larger slower species. Hence, the experimental design was adapted utilizing the geometry of the instrument, namely, quadrupole mass filter prior to the cIMS device and the presence of independent collisional activation and ion storage regions sited before and after the cyclic IMS device. Furthermore, collision-induced dissociation (CID), primarily leading to a dealkylation, was used to gain additional structural information. We were able to distinguish structural groups of polycyclic aromatic hydrocarbons and heterocycles (PAH/PASH). Up to 10 passes in the cyclic ion mobility device, accounting for a separation length of approx. 10 m, were deployed resulting in two distributions (Figure 1, a). Finally, we introduce a data processing workflow to resolve the 3.4 mDa SH4/C3 mass split by combining the ion mobility and mass spectrometric resolving power (Figure 1, b). The authors believe that cyclic ion mobility with intelligent design of experiment (DoE) and optimized processing routines will be a powerful approach addressing the isobaric and isomeric complexity of ultra-complex petroleum mixtures.

Exploring complex mixtures by cyclic ion mobility high-resolution mass spectrometry

ACS Fall 2021

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