Ultrahigh-resolution mass spectrometry has allowed the determination of elemental formulas of the compounds comprising crude oils. However, elucidating molecular structures remains an analytical challenge. Herein, we propose and demonstrate an approach combining ion mobility mass spectrometry (IM-MS), ultrahigh-resolution mass spectrometry, and theoretical collisional cross-section (CCS) calculations to determine the molecular structures of aromatic compounds found in crude oils. The approach is composed of three steps. First, chemical structures are suggested based on the elemental formulas determined from ultrahigh-resolution mass spectra. Second, theoretical CCS values are calculated based on these proposed structures. Third, the calculated CCS values of the proposed structures are compared with experimentally determined CCS values from IM-MS data to provide proposed structures. For proof of concept, 31 nonalkylated and short-chain alkyl (n < 5, (CH2)n) aromatic compounds commonly observed in crude oils were analyzed. Theoretical and experimental CCS values matched within a 5% RMS error. This approach was then used to propose structures of compounds in selected m/z regions of crude oil samples. Overall, the combination of ion mobility mass spectrometry, ultrahigh-resolution mass spectrometry, and theoretical calculations was shown to be a useful tool for elucidating chemical structures of compounds in complex mixtures.

Because of its high molecular complexity, ultra high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) is used to characterize heavy petroleum distillates. However, high peak capacity can also be obtained with ion mobility-mass spectrometry (IM-MS). In this case, the additional separation dimension allows for the compensation of the lower resolving power of the time-of-flight mass analyzer. The processing and elemental composition assignments from such bidimensional IM-MS data cannot be achieved with conventional software packages. PetroOrg, a new software package, was used to compare IM-MS data sets recorded with atmospheric solid analysis probe (ASAP) and three other atmospheric pressure ionization sources. The choice of the ionization source is indeed very critical as it defines the type of compounds that can be detected from mixtures. Electrospray ionization (ESI) is very specific to polar compounds and yields relatively simple data sets that can be readily attributed to nitrogen containing compounds allowing their speciation. On the other hand, gas phase ionization methods such as APCI, APPI, and ASAP yielded valuable information concerning thiophenic species. However, in this case the IM-MS peak capacity is not sufficient to separate all isobaric species. It is worth noting that ASAP and APPI yielded similar mass spectra although the ASAP ionization mechanism is believed to be closer to that of APCI. Most likely this is due to the absence of solvent with ASAP that reinforces charge exchange processes and therefore affords low ionization discrimination such as with APPI.

International audienceIon mobility-mass spectrometry is starting to be considered as a useful tool in the deconvolution of complex oil and petroleum samples. While ultrahigh resolution mass spectrometry is the incumbent technology in this field, ion mobility offers complementary information related to species size and shape, and also the ability to resolve structural isomers. In this work, a sample of the resins portion of the Saturates, Aromatics, Resins, and Asphaltenes (SARA) fractions of crude oil was analysed using an orthogonal acceleration quadrupole time-of-flight mass spectrometer (oa-QToF MS) that incorporates a travelling wave ionmobility spectrometry (TWIMS) region. The ion mobility data were compared with previously acquired ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) data and various nitrogen containing families were identified. Ion mobility data were processed in the typical way for the oil and petroleum industry; and the use of high resolution exact mass coupled with mobility data to provide enhanced species resolution was examined. Double bond equivalence (DBE) and carbon number groups were identified using patterns in the ion mobility data, which demonstrated the utility of ion mobility for discovering species relationships within the crude oil sample. The ability to calibrate the ion mobility cell and generate sizes for the detected ions was also recognised as potentially having particular value for the implementation of conversion or hydrotreatment processes in the oil industry

Ion mobility coupled with mass spectrometry was proven to be an efficient way to characterize complex mixtures such as petroleum samples. However, the identification of isomeric species is difficult owing to the molecular complexity of petroleum and no availability of standard molecules. This paper proposes a new simple indicator to estimate the isomeric content of highly complex mixtures. This indicator is based on the full width at half maximum (FWHM) of the extracted ion mobility peak measured in millisecond or square angstrom that is corrected for instrumental factors such as ion diffusion. This value can be easily obtained without precisely identifying the number of isomeric species under the ion mobility peaks. Considering the Boduszynski model, the ion mobility profile for a particular elemental composition is expected to be a continuum of various isomeric species. The drift time-dependent fragmentation profile was studied and confirmed this hypothesis, a continuous evolution of the fragmentation profile showing that the larger alkyl chain species were detected at higher drift time values. This new indicator was proven to be a fast and efficient method to compare vacuum gas oils for which no difference was found using other analytical techniques. Graphical Abstract ᅟ.

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.