Characterization of Deasphalted Crude Oils Using Gas Chromatography–Atmospheric Pressure Laser Ionization–Trapped Ion Mobility Spectrometry–Time-of-Flight Mass Spectrometry

In
the present work, a novel workflow based on complementary gas-phase
separations is applied to the characterization of deasphalted light
(Macondo and Calvert), medium (Duri), and heavy (San Ardo) crude oils.
The coupling of gas chromatography (GC), atmospheric pressure laser
ionization (APLI), and trapped ion mobility spectrometry–mass
spectrometry (TIMS–MS) resulted in the effective separation
and candidate assignment of polycyclic aromatic hydrocarbons (PAHs)
and similar compounds. The analytical power of GC–APLI–TIMS–TOF
MS is based on the separation of the isomeric content using the GC
and TIMS (R = 50–90 with Sr = 0.18 V/ms) gas-phase separations, followed by the
high mass resolution and mass accuracy (<2 ppm) of the TOF MS analyzer.
Previously reported PAH-like known compounds (130 compounds) uniquely
assigned on the basis of their retention time (RT), collisional cross
section (CCS), and mass-to-charge ratio (m/z) showed signature patterns and distinctive diagnostic
ratios representative of the thermal maturity, lithology, and microbial
contribution to each oil formation. The unsupervised T-Rex 4D analysis
of GC–APLI–TIMS–TOF MS generated for the first
time an exhaustive list of PAHs and similar unknown components (∼8500),
with each component characterized by a RT, CCS, m/z value, and chemical formula and peak areas for
each replica analysis (i.e., 12 total, 3× per crude oil). The
inspection of the PAHs and similar unknown compounds provided a list
of unique identifiers for each crude oil (2–4% of the assigned
compounds) as well as molecular components common to all crude oils
(∼50% of the assigned compounds). The analytical power of GC–APLI–TIMS–TOF
MS is illustrated using unsupervised principal component analysis
(PCA), where the four oils can be easily separated in two principal
components that account for 70% of the total variance.