8 research outputs found
Calculation of the Total Sulfur Content in Crude Oils by Positive-Ion Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry
Herein,
a method to calculate the total sulfur concentration in
petroleum samples from the chemometric modeling of data obtained by
positive-ion atmospheric pressure photoionization Fourier transform
ion cyclotron resonance mass spectrometry [(+) APPI FT-ICR MS] is
described. Analysis by FT-ICR MS provides both a measurement of the
total sulfur concentration and detailed molecular-level speciation
of sulfur-containing compounds. A total of 30 crude oil samples ranging
from 0.2 to 4.6 wt % sulfur were employed to train the sulfur prediction
model. The ratios of the percent relative abundance (%RA) between
the sulfur classes (S<sub><i>x</i></sub>) and the hydrocarbon
(HC) class were employed as variables for principal component analysis
(PCA). The PCA results reveal a highly linear trend along the principal
component with the highest explained variance (PC1). Analysis of the
loadings plot reveals that the S<sub>1</sub>/HC ratio governs the
trend in PC1. Values for PC2 are governed by S<sub>1</sub>/HC, S<sub>2</sub>/HC, and S<sub>3</sub>/HC ratios and provide the ability to
distinguish between oils with higher total sulfur contents (greater
relative abundance of S<sub>2</sub>- and S<sub>3</sub>-containing
compounds for sulfur of >1 wt %). Thus, these results indicate
that
the sulfur concentration of crude oils can be modeled by a linear
combination of variables based on S<sub><i>x</i></sub>/HC
ratio(s). The model successfully predicted sulfur concentrations for
11 test samples within 0.36% standard deviation, as compared to sulfur
concentrations obtained from bulk elemental analysis
Calculation of the Total Sulfur Content in Crude Oils by Positive-Ion Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry
Herein,
a method to calculate the total sulfur concentration in
petroleum samples from the chemometric modeling of data obtained by
positive-ion atmospheric pressure photoionization Fourier transform
ion cyclotron resonance mass spectrometry [(+) APPI FT-ICR MS] is
described. Analysis by FT-ICR MS provides both a measurement of the
total sulfur concentration and detailed molecular-level speciation
of sulfur-containing compounds. A total of 30 crude oil samples ranging
from 0.2 to 4.6 wt % sulfur were employed to train the sulfur prediction
model. The ratios of the percent relative abundance (%RA) between
the sulfur classes (S<sub><i>x</i></sub>) and the hydrocarbon
(HC) class were employed as variables for principal component analysis
(PCA). The PCA results reveal a highly linear trend along the principal
component with the highest explained variance (PC1). Analysis of the
loadings plot reveals that the S<sub>1</sub>/HC ratio governs the
trend in PC1. Values for PC2 are governed by S<sub>1</sub>/HC, S<sub>2</sub>/HC, and S<sub>3</sub>/HC ratios and provide the ability to
distinguish between oils with higher total sulfur contents (greater
relative abundance of S<sub>2</sub>- and S<sub>3</sub>-containing
compounds for sulfur of >1 wt %). Thus, these results indicate
that
the sulfur concentration of crude oils can be modeled by a linear
combination of variables based on S<sub><i>x</i></sub>/HC
ratio(s). The model successfully predicted sulfur concentrations for
11 test samples within 0.36% standard deviation, as compared to sulfur
concentrations obtained from bulk elemental analysis
Advances in Asphaltene Petroleomics. Part 1: Asphaltenes Are Composed of Abundant Island and Archipelago Structural Motifs
For
decades, discussion of asphaltene structure focused primarily
on molecular weight. Now that it is widely accepted that asphaltene
monomers are between ∼250 and 1200 g/mol, disagreement has
turned to asphaltene architecture. The classic island model depicts
asphaltenes as single core aromatic molecules with peripheral alkyl
side chains, whereas the less widely accepted archipelago model, includes
multiple aromatic cores that are alkyl-bridged with multiple polar
functionalities. Here, we analyze asphaltene samples by positive-ion
atmospheric pressure photoionization Fourier transform ion cyclotron
resonance mass spectrometry and perform infrared multiphoton dissociation
to identify their aromatic core structures to shed light on the abundance
of island and archipelago structural motifs. Our results indicate
that island and archipelago motifs coexist in petroleum asphaltenes,
and unlike readily accessible island motifs, asphaltene purification
is required to detect and characterize archipelago species by mass
spectrometry. Moreover, we demonstrate that mass spectrometry analysis
of asphaltenic samples is biased toward the preferential ionization/detection
of island structural motifs and that this bias explains the overwhelming
mass spectral support of the island model. We demonstrate that the
asphaltene structure is a continuum of island and archipelago motifs
and hypothesize that the dominant structure (island or archipelago)
depends upon the asphaltene sample
Advances in Asphaltene Petroleomics. Part 2: Selective Separation Method That Reveals Fractions Enriched in Island and Archipelago Structural Motifs by Mass Spectrometry
Advances
in high-resolution Fourier transform ion cyclotron resonance
mass spectrometry (FT-ICR MS) enable molecular-level characterization
of ultracomplex asphaltene samples. Such analyses most often reveal
compounds that are highly aromatic but alkyl-deficient in nature and,
thus, support the classical “island” model of asphaltene
architecture. However, recent works that combine chromatographic separations
with mass spectrometry for the analysis of crude oils have shown that
differences in ionization may greatly affect the analysis of complex
mixtures (known as the matrix effect). Simply, compounds that ionize
with greater efficiency are preferentially observed and mask the detection
of poorly ionized compounds. Asphaltenes are not immune to this phenomenon.
In the first of this series (10.1021/acs.energyfuels.7b02873), it was demonstrated that asphaltenes generated by different precipitants
showed greatly varied monomer ion yields (ionization efficiencies).
This work focuses on the development of an extrography fractionation
method that selectively targets the removal of asphaltene species
that exhibit high monomer ion yields and, thus, restrict mass spectral
characterization of less efficiently ionized species. Silica gel was
used as the stationary phase, and a unique solvent series separated
asphaltenes based on their interaction with the silica surface, which
was later determined to depend heavily upon the structure as well
as monomer ion yield. The first two solvents (acetone and acetonitrile)
isolated compounds that most efficiently produce monomeric asphaltene
ions and, thus, cause bias in mass spectrometric analyses of whole
asphaltenes. A solvent polarity gradient was then used, with <i>n</i>-heptane, toluene, tetrahydrofuran, and methanol, to separate
remnant asphaltene compounds on the basis of polarity and structure.
Our results demonstrate that mass spectrometry of whole asphaltenes
does not reveal the complete molecular composition but rather preferentially
exposes highly aromatic, alkyl-deficient, island-type structures.
Early eluting fractions are shown to resemble the composition of the
whole asphaltene and are enriched in island structures, whereas the
analysis of later-eluting fractions reveals archipelago structural
motifs as well as species with atypical asphaltene molecular compositions.
We also demonstrate that, as molecular weight increases, the asphaltenes
exhibit increased contributions of archipelago structural motifs.
Higher mass ions (<i>m</i>/<i>z</i> > 550),
even
from asphaltene fractions enriched in island structures, exhibit fragmentation
pathways that originate from archipelago structures. Thus, positive-ion
atmospheric pressure photoionization (APPI) FT-ICR MS provides molecular-level
data that suggest that the island model is not the dominant structure
of asphaltenes. It coexists with abundant archipelago structures,
and the ratios of each are sample-dependent
Chromatographic Enrichment and Subsequent Separation of Nickel and Vanadyl Porphyrins from Natural Seeps and Molecular Characterization by Positive Electrospray Ionization FT-ICR Mass Spectrometry
We report a novel chromatographic
method to enrich and separate
nickel and vanadyl porphyrins from a natural seep sample and combine
molecular level characterization by positive-ion electrospray ionization
Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR
MS). Vanadyl and nickel porphyrin model compound elution from primary
secondary amine (PSA) stationary phase combined with UV-vis spectroscopy
confirms enrichment and subsequent fractionation of nickel and vanadyl
porphyrins into polarity-based subfractions. A more than 100-fold
increase in signal-to-noise ratio for nickel porphyrins enables unequivocal
elemental composition assignment confirmed by isotopic fine structure
for all isotopes >1% relative abundance, and the first mass spectral
identification of <sup>61</sup>Ni porphyrin isotopologues derived
from natural seeps. Oxygen-containing vanadyl porphyrins and sulfur-containing
vanadyl porphyrins are isolated in the same fraction simultaneously
from the same sample. We provide the first chromatographic evidence
of carboxylic acid functionalities peripheral to the porphyrin core,
in agreement with previous studies
Chromatographic Enrichment and Subsequent Separation of Nickel and Vanadyl Porphyrins from Natural Seeps and Molecular Characterization by Positive Electrospray Ionization FT-ICR Mass Spectrometry
We report a novel chromatographic
method to enrich and separate
nickel and vanadyl porphyrins from a natural seep sample and combine
molecular level characterization by positive-ion electrospray ionization
Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR
MS). Vanadyl and nickel porphyrin model compound elution from primary
secondary amine (PSA) stationary phase combined with UV-vis spectroscopy
confirms enrichment and subsequent fractionation of nickel and vanadyl
porphyrins into polarity-based subfractions. A more than 100-fold
increase in signal-to-noise ratio for nickel porphyrins enables unequivocal
elemental composition assignment confirmed by isotopic fine structure
for all isotopes >1% relative abundance, and the first mass spectral
identification of <sup>61</sup>Ni porphyrin isotopologues derived
from natural seeps. Oxygen-containing vanadyl porphyrins and sulfur-containing
vanadyl porphyrins are isolated in the same fraction simultaneously
from the same sample. We provide the first chromatographic evidence
of carboxylic acid functionalities peripheral to the porphyrin core,
in agreement with previous studies
Advanced Chemical Characterization of Pyrolysis Oils from Landfill Waste, Recycled Plastics, and Forestry Residue
Waste material pyrolysis
has proven useful for the production of
pyrolysis oils; however, the physical properties and chemical composition
of pyrolysis oils are greatly influenced by the feedstock. It is well
established that lignin- and cellulose-rich material produces pyrolysis
oils high in aromatic oxygen-containing compounds, whereas pyrolysis
oils produced from other sources such as plastics and household wastes
are far less characterized. Here, three fast pyrolysis oils produced
from landfill waste, recycled plastics, and pine forestry residue
are compared by elemental analysis, Fourier transform infrared spectroscopy
(FT-IR), comprehensive 2D gas chromatography (GC×GC), Fourier
transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and
liquid chromatography. GC×GC, FT-ICR MS, and liquid chromatography
provide insight into the chemical composition of pyrolysis oils, whereas
FT-IR analysis identifies functional groups. Landfill and plastic
pyrolysis oils were found to contain higher hydrocarbon content that
resulted from little or no cellulosic material in their feedstock.
In contrast, pine pyrolysis oil is more aromatic and contains a higher
abundance of polar species due to the number of oxygen functionalities.
The hydrocarbons in plastic pyrolysis oil are more saturated than
in landfill and pine pyrolysis oils. Due to their lower oxygen content,
landfill and plastic pyrolysis oils are more attractive than pine
pyrolysis oil as potential fuel candidates
Dual-Column Aromatic Ring Class Separation with Improved Universal Detection across Mobile-Phase Gradients via Eluate Dilution
The herein described
High Performance Liquid Chromatography (HPLC)
platform (termed HPLC-3) combines a complex solvent gradient with
two electron acceptor columns to provide aromatic ring class (ARC)
separation for heavy oils. The separation yields seven major fractions:
saturates, monoaromatics (1 ring), diaromatics (2 rings), triaromatics
(3 rings), tetra-aromatics (4 rings), polyaromatics and polars (5+
polars), and aliphatic sulfides. The system utilizes a photodiode
array detector (PDA) for online measurements of aromaticity in series
with an evaporative light scattering detector (ELSD) to provide improved
quantitative mass determination across the entire solvent gradient.
A new postcolumn dilution strategy was successfully utilized to compensate
for solvent effects on the ELSD signal. The method allows for calibration
across the entire HPLC-3 solvent gradient and simultaneously diverts
∼90% of the sample effluent for fraction collection and further
characterization. In addition to the major ARC fractions, the retention
characteristics of various heteroatomic functional groups were studied
to demonstrate the HPLC-3 system’s ability to further separate
polar compounds on the basis of hydrogen bonding