Isolation of Crude Oil Peaks Differing by m/ z ∼0.1 via Tandem Mass Spectrometry Using a Cyclic Ion Mobility-Mass Spectrometer

Mass spectrometry is widely used in studying the structures of compounds present in crude oil. In this study, a novel mass spectrometer incorporating a cyclic ion mobility separator was used to obtain tandem mass spectra of crude oil compounds in a narrow mass-to-charge ratio (m/z) window. Isolation of specific peaks was performed by combining quadrupole and ion mobility separation. As a result, peaks differing by an m/z value of 0.1 could be isolated. Tandem mass spectrometry with collision-induced dissociation was successfully performed to study the chemical structures of the isolated ions. A series of ions ranging from m/z 374 to m/z 384, differing by two hydrogen atoms but with the same number of carbons, were isolated and tandem mass spectra were obtained. The higher m/z precursor ions produced smaller fragment ions; this is explained by the reduced aromaticity owing to an increased number of hydrogen atoms. The ions at m/z 388 and 374, differing by a CH₂ group, produced very similar fragmentation patterns. Overall, the data obtained from this study clearly demonstrate that the novel cyclic ion mobility-mass spectrometer is a powerful instrument that can provide tandem mass spectra of individual compounds constituting complex mixtures such as crude oils.