Interpreting Chemical Structures of Compounds in Crude Oil Based on the Tandem Mass Spectra of Standard Compounds Obtained at the Same Normalized Collision Energy

Abstract

In this study, the tandem mass spectra of 25 standard compounds, obtained at a normalized collision energy of 50, were used to investigate the structures of crude oil. The product ion distributions of these standard compounds were dependent on the number and length of their alkyl side chains. Long alkyl side chains (C n H2n , n ≥ 5) were easily lost during molecular collision, leaving behind methyl groups on the aromatic cores. In contrast, compounds with short interlinking alkyl chains (C n H2n , n ≤ 1) were not significantly fragmented, and a decrease in the double bond equivalent (DBE) value was observed when compounds had saturated rings. Based on the derived observations, the possible structures of S1-class compounds with DBE values of 6, 7, 8, and 9 were suggested. It was also determined that, in the tandem mass spectra of crude oil fractions, (1) a series of peaks separated by CH2 groups were generated from isomers with different numbers of alky side chains, (2) the number of methyl groups left after molecular collision was positively correlated to the quantity of branched molecules, and (3) significant fragmentation did not occur for aromatic cores linked by short alkyl chains (C n H2n , n ≥ 2), and hence, archipelago structures with short alkyl linkage could not be excluded based solely on tandem mass spectra. This study clearly shows that a systematic analytical approach using a well-defined set of standard compounds combined with tandem mass spectrometry can significantly improve our understanding on the chemical structures of crude oil compounds.

Analysis of environmental organic matters by Ultrahigh‐Resolution mass spectrometry—A review on the development of analytical methods

“…Tandem MS is the most widely used technique for examining the chemical structures of analytes in various types of organic mixtures (Capley et al, 2010;Ha et al, 2017;Osterholz et al, 2015;Reemtsma et al, 2008;Stenson et al, 2003;Witt et al, 2009;Zark et al, 2017). A neutral CO 2 loss is commonly observed in the tandem MS data of EOM.…”

Non‐target profiling of bitumen‐influenced waters for the identification of tracers unique to oil sands processed‐affected water (OSPW) in the Athabasca watershed of Alberta, Canada

“…The chromatographic separation was improved by using SFC (Figure S7, supporting information), and the SFC peak at 8.2 min was determined to correspond to the peak at 18.7 min detected by HPLC/Orbitrap HRMS, based on the consistency of this ion being detected in the OSPW‐A, OSPW‐B‐1, GW‐2C and GW‐DP5 samples, and being absent in the method blank, BG‐3 and BG‐6 samples. SFC/Orbitrap MS/MS analysis was performed on the m/z 213.1644 ion at 8.2 min, and the spectrum showed a series of product ions separated by 14 m/z units (CH 2 ) indicative of a linear alkyl chain 53 . The double‐bond equivalent number (DBE = 7) of this entity (C 16 H 20 ) indicated the probable existence of a naphthalene structure.…”

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

“…For instance, loss of an ethyl or propyl group will yield two fragment ions separated by the mass of CH 2 . Previous studies have demonstrated that the fragmentation pattern can be used to elucidate the core structures of crude oil compounds. − …”

“…Tandem mass spectrometry with collision-induced dissociation (CID) or infrared multiphoton dissociation coupled with UHR-MS has been used to study fragmentation patterns of crude oil compounds. − For example, CID was used to elucidate the maximum number of carbons in the alkyl chains and chemical structures of compounds in chromatographically simplified vacuum gas oil . The fragmentation patterns helped to understand core structures of oil compounds. ,− …”