Lacustrine versus Marine Oils: Fast and Accurate Molecular Discrimination via Electrospray Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and Multivariate Statistics

The ionizable molecular
composition of 36 lacustrine oil samples
and 29
marine oil samples from different off-shore Brazilian basins have
been screened by ultrahigh-resolution and accuracy Fourier transform
ion cyclotron resonance mass spectrometry with electrospray ionization
in the negative-ion mode [ESI(−)-FT-ICR MS]. The negative mode
has been demonstrated successfully to characterize source rock because
it favors the detection of heteroatomic compounds such as nitrogen-,
sulfur-, and oxygen-containing (NSO), which reveal information about
geochemical environmental. ESI(−)-FT-ICR MS data was processed
with a new approach that unifies information from the chemometrics
tool and petroleomics conventional data processing. Novel diagrams
were proposed that use variable important to projection (VIP), such
as molecular formula obtained, via partial least-square discriminant
analysis (PLS-DA) to plot in diagrams, such as those that display
double bond equivalence (DBE) versus number carbon atom (NCA) and
H/C ratio versus molecular mass (MM) trends. This new approach is
advantageous since it is able to verify and compare all samples at
once, obtaining more selective variables, such as molecular formula,
and with more confidence because the figures of merit are acquired
by statistical tests from PLS-DA, whereas it also provides the usual
information from petroleomics tools such DBE, NCA, H/C ratio, MM,
and molecular classes. This new approach revealed significant differences
in the molecular distribution of heteroatomic components for N-containing
and O-containing molecules (N class and O class) allowing a clear
separation of all samples in two groups of marine or lacustrine crude
oils.