Energy Fuels 2010, 24, 3572–3580
Published on Web 05/18/2010
: DOI:10.1021/ef1002364
)
Characterization of Nitrogen-Containing Compounds in Heavy Gas Oil Petroleum
Fractions Using Comprehensive Two-Dimensional Gas Chromatography Coupled to
Time-of-Flight Mass Spectrometry
Carin von M€
uhlen,† Eniz C. de Oliveira,‡ Claudia A. Zini,§ Elina B. Caram~ao,§ and Philip J. Marriott*,
)
†
Post-Graduation Program in Environmental Quality, Feevale University RS 239, 2755, CEP 93352-000,
Novo Hamburgo, Rio Grande do Sul (RS), Brazil, ‡Post-Graduation Program in Environment and Development, UNIVATES,
Lajeado, Rio Grande do Sul (RS), Brazil, §Chemistry Institute, Federal University of Rio Grande do Sul (UFRGS), Porto Alegre,
Rio Grande do Sul (RS), Brazil, and Australian Centre for Research on Separation Science, School of Applied Sciences,
RMIT University, GPO Box 2476, Melbourne 3001, Victoria, Australia.
Received March 2, 2010. Revised Manuscript Received May 5, 2010
Nitrogen (N)-containing compounds are naturally present in petroleum, and they are responsible for
several deleterious effects that reduce the quality of products and negatively affect the processes involved in
the upgrading of feedstock. The speciation of such compounds in petroleum heavy fractions is still a
challenge. In the present work, N-containing compounds were characterized in heavy gas oil (HGO)
fractions using a solid-liquid fractionation scheme and comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry. Classification and identification of compounds
were carried out based on seven different categories of analytical information viz. retention times in first
and second dimensions, analytical standards co-injection, the structured pattern of the separation space,
the structured pattern of the separation space with the selection of specific m/z values, the library mass
spectra match factor, and the characteristic deconvoluted mass spectra. All of these interpretations were
available from a single analytical run followed by a standard injection. Compounds were extracted from
the sample using an ion-exchange resin method to separate neutral and basic N-containing compounds,
after a pre-fractionation step, using neutral aluminum oxide. This methodology allowed for the identification of 120 N-containing compounds and tentative identification of a further 108 compounds using their
deconvoluted characteristic mass spectra as a basis for identification. Identified components included
alkyl-indols, alkyl-carbazols, alkyl-benzocarbazols, alkyl-quinolines, alkyl-indene-pyridines, alkyl-benzoquinolines, and alkyl-dibenzoquinolines.
compounds be understood,6 as well as the mechanism of
catalytic processes.7,8 The identification of N-containing
compounds in petrochemical samples is a challenge because
of the presence of multiple isomers, for a range of different
compound classes, in a very complex mixture, with generally a
relatively low concentration of the compounds. As an example, the total N content of about 90% of crude oils is less than
2%.9 Because heavy gas oil (HGO) is an intermediary fraction
from vacuum distillation of the residue of the atmospheric
distillation of crude oil,10 a higher concentration of heavy
N-containing compounds is expected.
A common approach for the analysis of N-containing
compounds in several petrochemical samples is to increase
the relative concentration and/or minimize the sample complexity, by fractionating N compounds into two different
groups: neutral pyrrolic type and basic pyridinic type.11 The
Introduction
Basic nitrogen (N)-containing compounds are responsible
for poisoning of acidic sites in catalytic fluid processes and
hydrocracking zeolite catalysts.1 The extent of poisoning is
dependent upon the specific N compounds in the feedstock,
and it is a function of their gas-phase basicity.2,3 Poisoning
reduces the hydrotreating catalyst activity, thus restricting the
ability to attain low-sulfur fuel specifications.4 Upon combustion, they form N-oxides (NOx), which contribute to engine
corrosion and air pollution. Certain N compounds are responsible for fuel storage instability.5 These various consequences attributed to N-containing compounds in crude oils
demand that detailed structure, reactivity, and origin of those
*To whom correspondence should be addressed: Australian Centre for
Research on Separation Science, School of Applied Sciences, RMIT University, GPO Box 2476, Melbourne 3001, Victoria, Australia. Telephone:
þ61-3-9925-2632. Fax: þ61-3-9925-3747. E-mail: philip.marriott@rmit.
edu.au.
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pubs.acs.org/EF
Energy Fuels 2010, 24, 3572–3580
: DOI:10.1021/ef1002364
von M€uhlen et al.
GC GC with nitrogen chemiluminescence detection (NCD)
to separate N-containing compounds in diesel fuel, presenting
the “roof-tile effect” for indoles, carbazole quinolines, and
pyridines. Adam and co-workers32 showed quantitative studies
on diesel samples and liquefied coal samples, using GCGCNCD for group-type analysis, and liquefied coal samples.15
In our previous study,33 quantitative analysis of N-containing
compounds in HGO, using GC GC-nitrogen phosphorus
detector (NPD) and two different fractionation methods, was
presented. N-Containing compounds equivalent to more than
2000 ppm total content of the oil were quantified, distributed
in classes, such as indoles, alkyl carbazoles ranging from C0 to
C6þ, alkyl benzocarbazoles ranging from C0 to C4þ, alkyl
quinolines, and alkyl benzoquinolines. Several compounds
were quantified for the first time in this kind of sample, with
an acceptable structure of the separation space. However, it
was not possible to identify unexpected compounds, although
they were fully separated on the chromatogram. Adam and
co-workers15 recently presented the application of GC GC/
TOFMS for identification of N-containing compounds in
diesel and liquefied diesel samples. Co-elution of different
N-containing compound classes in the same region was observed; this prevents adequate identification when a N-selective
detector is employed. Although the compounds identified in
the study by Adam and co-workers presented a molecularmass range significantly lower than expected in HGO samples,
the power of this analytical technique successfully demonstrated compound identification. Striebich and co-workers34
applied multi-dimensional GC/TOFMS to identify polar
compounds in aviation fuels, reporting quantitative results
for important polar classes, such as amines, indoles, pyridines,
anilines, sulfur compounds, oxygenates, aromatics, and others.
In the present study, analytical information provided by
GC GC/TOFMS analysis, such as retention times in first
(1tR) and second (2tR) dimensions, co-injection of analytical
standards, the structured pattern within the separation space
in the total ion diagram (TID), the structured pattern within
the separation space with selection of specific m/z values, the
library mass spectral match factor, and/or the characteristic deconvoluted mass spectra, was used to identify higher molecularmass N-containing compounds in HGO samples.
neutral N species usually comprise pyrrole, indole, carbazole,
and their higher alkylated and benzylated analogues. Basic
N species usually include pyridines, quinolines, benzoquinolines, and their alkylated derivatives. Extraction and concentration of N compounds have been performed by either liquid/
liquid extraction (LLE)12 or solid-phase extraction (SPE),13,14
although the quantitative fractionation of neutral and basic
N compounds is subject to continuing research.15
Several methods involving petroleum and petroleum product analysis of N-containing compounds have been developed using a variety of analytical techniques. These include
gas chromatography coupled to mass spectrometry (GC/
MS),12,14 GC equipped with a pulsed flame photometric detector (GC-PFPD) and ammonia chemical ionization MS,16
particle beam liquid chromatography/MS (LC/MS),17-19 mass
spectrometry with atmospheric pressure chemical ionization,20
positive-ion electrospray ionization MS (ESIþ),21 time-of-flight
secondary ion MS (TOF SIMS)22 and electron ionization, field
desorption ionization, and electrospray ionization Fourier transform ion cyclotron resonance MS (FT-ICR MS).8 Although several
fractionation steps and the most powerful analytical instrumentation may be employed, it is still not possible to speciate
(separate) all N-containing compounds in petroleum samples.
Comprehensive two-dimensional GC (GCGC) is a powerful analytical technique that has been applied to petrochemical samples since its inception,23-27 and this persists as one of
the key GC GC applications. GC GC offers much more
informing power and separation power than conventional GC
separations.28,29 The presence of ordered structures in 2D
separation space30 is a unique attribute of GCGC that often
allows for unequivocal chemical compound classification
and identification through a visual inspection of the contour
plots. Wang and co-workers31 demonstrated the capability of
(12) Pasquale, A. J.; Bauserman, J. M.; Mushrush, G. W. Pet. Sci.
Technol. 2009, 27 (18), 2192–2199.
(13) da Luz, E. R.; Gonsalves, T. F. M.; Aucelio, R. Q. J. Sep. Sci.
2009, 32 (12), 2058–2065.
(14) Oliveira, E. C.; Campos, M. C. V.; Lopes, A. S.; Vale, M. G. R.;
Caram~
ao, E. B. C. J. Chromatogr., A 2004, 1027, 171–176.
(15) Adam, F.; Bertoncini, F.; Dartiguelongue, C.; Marchand, K.;
Thiebaut, D.; Hennion, M. C. Fuel 2009, 88, 938–946.
(16) Shi, Q.; Xu, C. M.; Zhao, S. Q.; Chung, K. H. Energy Fuels 2009,
23, 6062–6069.
(17) Mao, J.; Pacheco, C. R.; Traficante, D. D.; Rosen, W.
J. Chromatogr., A 1994, 684 (1), 103–111.
(18) Mao, J.; Pacheco, C. R.; Traficante, D. D.; Rosen, W. Fuel 1995,
74 (6), 880–887.
(19) Mao, J.; Pacheco, C. R.; Traficante, D. D.; Rosen, W. J. Liq.
Chromatogr. 1995, 18 (5), 903–916.
(20) Cheng, X.; Zhao, T.; Fu, X.; Hu, Z. Fuel Process. Technol. 2004,
85 (13), 1463–1472.
(21) Qian, K.; Edwards, K. E.; Diehl, J. H.; Green, L. A. Energy Fuels
2004, 18 (6), 1784–1791.
(22) Toporski, J.; Steele, A. Org. Geochem. 2004, 35 (7), 793–811.
(23) Blomberg, J.; Schoenmakers, P. J.; Beens, J.; Tijssen, R. J. High
Resolut. Chromatogr. 1997, 20 (10), 539–544.
(24) Vendeuvre, C.; Ruiz-Guerrero, R.; Bertoncini, F.; Duval, L.;
Thiebaut, D. Oil Gas Sci. Technol. 2007, 62 (1), 43–55.
(25) Venkatramani, C. J.; Phillips, J. B. J. Microcolumn Sep. 1993, 5
(6), 511–516.
(26) von M€
uhlen, C.; Zini, C. A.; Caram~ao, E. B.; Marriott, P. J.
Quim. Nova 2006, 29 (4), 765–775.
(27) von M€
uhlen, C.; Zini, C. A.; Caram~ao, E. B.; Marriott, P. J.
J. Chromatogr., A 2006, 1105, 39–50.
(28) Kidwell, D. A.; Riggs, L. A. Forensic Sci. Int. 2004, 145 (2-3),
85–96.
(29) Marriott, P. J.; Morrison, P. D.; Shellie, R.; Dunn, M. S.; Sari, E.;
Ryan, D. LCGC Europe 2003, 16 (12A), 23–31.
(30) Marriott, P. J.; Massil, T.; H€
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1284.
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Experimental Section
Samples and Chemicals. Indole, carbazole, quinoline, iso-quinoline, 5,6-benzoquinoline, 7,8-benzoquinoline, and 7-H-dibenzo-c,
g-carbazole standards were purchased from AccuStandard, Inc.
(New Haven, CT). Dichloromethane (analytical grade) supplied
from Merck (Kilsyth, Victoria, Australia) was used to prepare the
standard solutions and for sample dilution.
The HGO residue was produced by Petrobras, in Brazil. This
sample presented a total acidity number of 0.15 mg of KOH g-1.
A prefractionation step was performed using a neutral aluminum oxide chromatographic column (CC) providing separation
of compounds in the following groups: hydrocarbons, resins
(compounds of low molecular mass and intermediate polarity),
and asphalthenes (polar compounds with high molecular
mass). These fractions were eluted using hexane (F1), n-hexane/
dichloromethane (F2), dichloromethane (F3), and methanol
(F4) in triplicate. Resins (F3) were further fractionated using
(32) Adam, F.; Bertoncini, F.; Brodusch, N.; Durand, E.; Thiebaut,
D.; Espinat, D.; Hennion, M. C. J. Chromatogr., A 2007, 1148 (1), 55–64.
(33) von M€
uhlen, C.; Oliveira, E. C.; Morrison, P. D.; Zini, C. A.;
Caram~ao, E. B.; Marriott, P. J. J. Sep. Sci. 2007, 30, 3223–3232.
(34) Striebich, R. C.; Contreras, J.; Balster, L. M.; West, Z.; Shafer,
L. M.; Zabarnick, S. Energy Fuels 2009, 23, 5474–5482.
3573
Energy Fuels 2010, 24, 3572–3580
: DOI:10.1021/ef1002364
von M€uhlen et al.
Figure 1. TID obtained with GC GC/TOFMS from a neutral fraction of a HGO sample: (A) without classification and (B) with classification
regions presented. In panel B, IC stands for alkyl-indoles (I) from C0 to C3 on the upper left part of the TID, CC located at the lower region
of the TID corresponds to alkyl-carbazoles from C0 to C12, and in the upper part of the TID, BC C corresponds to alkyl-benzocarbazoles from
C0 to C6.
Figure 2. Total ion chromatogram (TIC) and selected ions used to demonstrate MS deconvolution of peaks: 583-2, second modulated peak of
tetramethylphenanthrene; 580-B, base modulation of pentamethylcarbazole; 584-1 and 581-B, modulated non-identified peaks.
3574
Energy Fuels 2010, 24, 3572–3580
: DOI:10.1021/ef1002364
von M€uhlen et al.
ion-exchange resins (Amberlyst A-27 and A-15), providing basic
and neutral compound separation, also in triplicate. This fractionation procedure was previously described.14
GC GC/TOFMS System. The GC GC system comprised
a 6890 GC (Agilent Technologies, Burwood, Australia), retrofitted with an Everest model longitudinally modulated cryogenic
system (LMCS, Chromatography Concepts, Doncaster, Australia),
coupled to a TOFMS from LECO, Model Pegasus II. The
instrument was equipped with a model 6873 auto-sampler and
ChromaTOF 2.2 software.
The column set used consists of a nonpolar first dimension (1D)
capillary column BPX5 phase (5% phenyl polysilphenylenesiloxane) with dimensions of 30 m length 0.25 mm inner
diameter 0.50 μm film thickness (df) serially coupled with a
polar second dimension (2D) capillary column BPX50 phase
(50% phenyl polysilphenylene-siloxane) with dimensions of
1.0 m length0.15 mm inner diameter0.15 μm df. Both columns
were from SGE International (Ringwood, Australia). A transfer
line with dimensions of 0.5 m0.10 mm inner diameter was used
to couple the second-dimension column to the TOFMS.
A conventional split/splitless injector was used at 300 °C, with
an injection volume of 2.0 μL in pulse splitless mode, with a split
flow of 50 mL min-1 1 min after injection and 20 mL min-1
2 min after injection. Oven temperature program conditions were
as follows: initial temperature of 60 °C for 0.2 min, programmed
at 20 °C min-1 until 170 °C (hold for 5 min), and then 2 °C min-1
to 290 °C (hold for 20 min). A constant helium carrier gas flow of
1.0 mL min-1 was applied throughout the whole analysis after
pulse splitless injection (flow of 51 mL min-1 for 1 min). The MS
transfer line temperature was 350 °C, and the ion source temperature was 200 °C. Data were collected over a mass range of 45415 units at a data acquisition rate of 100 Hz. The detector voltage
was -1.90 kV, and 70 eV was employed for electron ionization.
The thermostatically controlled cryogenic trap was maintained
at about 40 °C from 4 min to the end of the run, and the modulation period was 6 s, commencing at 4 min to the end of the run.
Data Handling. Identification of N-containing compounds in
basic and neutral fractions of HGO samples was carried out
based on seven categories of analytical information, when
available: retention times in first (1tR) and second (2tR) dimensions, co-injection of analytical standards, the structured pattern of the separation space in the TID, the structured pattern of
the separation space observed when specific m/z values were
selected [defined as the selected ion diagram (SID)], the library
mass spectral match factor, and/or the characteristic deconvoluted mass spectra alone. The latter spectral data were interpreted on the basis of first principles because several compounds
(especially isomers) are not listed in the National Institute of
Standards and Technology (NIST) library used (version 2). For
data processing, ChromaTOF software, version 3.25, was used.
Results and Discussion
Figure 3. SID obtained with GC GC/TOFMS for a neutral fraction of a HGO sample. (A) IC represents alkyl-indoles from C0 to
C3. (B) CC at the lower region of the TID corresponds to alkylcarbazoles from C0 to C12. (C) BC C corresponds to alkyl-benzocarbazoles from C0 to C6. Selected ions are presented in Table 1.
Fractionation of HGO Samples. The recovery (m/m) of the
separate HGO fractions were F1, 35 ( 4.9%; F2, 26 ( 0.15%;
F3, 4.2 ( 0.52%; and F4, 7.4 ( 0.12%. The largest fraction
of compounds in HGO consists of saturated and aromatic
hydrocarbons (F1 þ F2, 61%). N-Containing compounds
were concentrated in the resin fraction (F3), and it was further separated into neutral and basic fractions, which was
found to be important to allow for the identification of compounds even with the use of GC GC/TOFMS. A separate
study was performed without fractionation of the sample
(results not shown), and it was not possible to identify most
of the N-containing compounds presented here. On the other
hand, direct identification of those compounds in a pure
sample (without fractionation) may be possible if a higher
concentration of N-containing compounds is present, although
trace level components will still be difficult.
Column Set. A 1D BPX5 column and a 2D BPX50 column
were employed, which is a commonly used set for petrochemical samples.27,31 Adam and co-workers15,32 used cyanopropyl (CNP) and polyethylene glycol (PEG) columns for the
2
D phase to improve the separation of neutral and basic
N-containing compounds. This type of column can be useful
to achieve a better separation for low-molecular-weight polar
compounds in 2D, such as anilines, quinolines, and indols. On
the other hand, the relatively low upper temperature limit of the
CNP and PEG columns limits the separation to low-molar-mass
compounds, because their maximum temperatures are around
250 and 280 °C, respectively, compared to 360 °C or higher for
a 50% phenyl column. Thus, these polar 2D CNP and PEG
phase columns cannot be applied for HGO analysis, because a
higher boiling point range is required for the N-containing
compounds of this HGO fraction.
3575
Energy Fuels 2010, 24, 3572–3580
: DOI:10.1021/ef1002364
von M€uhlen et al.
Table 1. Selected m/z Values, Characteristic of N-Containing Compounds
compounds
typical neutral fraction
alkyl-indoles
C0
C1
C2
C3
C4
C5
alkyl-carbazoles
C0
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
m/z
117
131
145
159
173
187
167
181
195
209
223
237
251
265
279
293
307
compounds
C11
C12
C13
alkyl-benzocarbazoles
C0
C1
C2
C3
C4
C5
C6
typical basic fraction
alkyl-quinolines
C0
C1
C2
C3
C4
C5
C6
Identification of Compounds in the Neutral Fraction. A TID
experimentally obtained for a neutral fraction of HGO is
illustrated in Figure 1A. Automated integration with spectral deconvolution of this chromatogram resulted in more
than 10 000 compounds in the peak table. Alkyl-carbazoles
and alkyl-benzocarbazoles were expected in the central region
of the TID, similar to the findings in our previous work using
GC GC-NPD33 for the same sample under similar conditions. In addition to the presence of N-containing compounds, this region also includes polyaromatic hydrocarbons
(PAHs) and other compounds, such as saturated hydrocarbons, which may not be expected in this fraction of HGO,
because of presumably incomplete elution of hydrocarbons
in the previous fractionation step. PAHs are detected by
TOFMS but not by the NPD used previously. PAHs exhibit
wrap-around in the color plot, and saturated hydrocarbons
are present in this extract but in low concentrations, as illustrated in Figure 1A. It is important to point out that most of
those compounds were removed in fractions 1 and 2 (61% of
the sample), but they are still present in fraction 3, because
of the high complexity of the sample. Because the resolution
of those compounds was not the aim of the present work, the
presence of this wrap-around effect was not considered a
problem. With the focus on selected ions from processed data,
all efforts in the method optimization were applied to chromatographically resolve N-containing compounds as completely as
possible, maintaining the roof-tile structure for those compounds, as can be observed in Figure 1B and Figure 2.
Even with the best chromatographic resolution possible,
the alkyl-carbazole region still coelutes with PAHs and other
compounds. Several of those compounds were resolved just
by mass spectra deconvolution, such as pentamethylcarbazole, illustrated in Figure 2. Each vertical line in Figure 2
represents a deconvoluted peak with S/N higher than 10,
which means that four peaks were deconvoluted with the
same 2D retention time (1tR, in s), in a 0.9 s 2tR window. The
PAH eluting just before pentamethylcarbazole presented the
same 237 and 222 masses as pentamethylcarbazole. Thus,
deconvolution will not be possible with a quadrupole MS
(even with GCGC operation), because of the peak skewing
of mass spectra over the peak and the lower acquisition rate.
Because mass spectral fragmentation patterns of aromatic
N-containing compounds are very unique and easily recognized, their identification may be performed using MS library
m/z
compounds
321
335
349
alkyl-indene-pyridines
C0
C1
alkyl-benzoquinolines
C0
C1
C2
C3
C4
C5
C6
alkyl-dibenzoquinolines
C0
C1
C2
C3
C4
C5
217
231
245
259
273
287
301
129
143
157
171
185
199
213
m/z
167
181
179
193
207
221
235
249
263
229
243
257
271
285
299
searching of deconvoluted peaks for isomer classification;
however, specific isomer structural assignment is not available
in the absence of authentic standards. The generic molecular
structure of these compounds and characteristic ions were
investigated and presented in previous work using GC/MS
for standard compounds14 and are in agreement with the
patterns found in TOFMS mass spectra of the HGO sample.
Molecular ions from the selected spectra were used to identify class patterns in the separation space using SIDs. These
diagrams were used as basic information to construct a classification system superimposed on the GC GC diagram, using
the classification tool provided with ChromaTOF software.
All selected regions are presented in Figure 1B. Figure 3
shows an expansion of the respective classification regions.
The selected ions are listed in Table 1. Note that, from among
this list of N-compound molecular ions, only the C0 and C1
alkylcarbazoles and alkyl-indene-pyridines have equivalent
ions of m/z 167 and 181 but there is no coincidence of these
compounds in 2D space (see later); hence, their unique analysis is straightforward.
The selected ions were also found in non-N-containing
compounds outside the classification regions, as presented in
Figure 3. It illustrates that a single ion monitoring (SIM)
approach, using 1D GC/MS is not sufficient to isolate such
compounds, in this particular sample, and that the 2D positions in combination with the TID have more diagnostic
information. In addition, several peaks were detected inside
a classification region and presented characteristic mass spectra
expected for the selected class, but they were not automatically identified in the peak table. Because the number of compounds (especially for isomers and homologues) from each
class in the MS library is limited, several compounds were
accompanied by low match values following the MS library
search, although the limited number of similar mass spectra
in the library resulted in high probability (P) values. As an
example, just one reference spectrum for C5 benzocarbazoles
(pentamethylcarbazole) was available in the MS library, and
at least six compounds were detected with a similar mass
spectrum, in the same region of the separation space. For
benzocarbazole, there were four characteristic spectra in the
MS library, but none for other alkyl derivatives of that class.
A total of 50 compounds were identified by the NIST library
as N-containing compounds with similarity values (S) higher
than 800. These compounds are listed in Table 2.
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Energy Fuels 2010, 24, 3572–3580
: DOI:10.1021/ef1002364
von M€uhlen et al.
Table 2. Compounds Identified in the Neutral Fraction of
HGO Samples Based on the Structured Pattern within the
Separation Space and MS Library Match
number
1
2
tR (s)
name
S
R
P
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
558
636
666
678
756
780
810
816
924
942
984
1638
1806
1908
1920
1938
1956
1980
2070
2076
2100
2118
2130
2148
2178
2196
2202
2226
2226
2238
2256
2286
2292
2316
3.67
4.25
4.36
4.46
4.66
4.88
4.89
5.02
5.18
5.21
5.42
2.19
1.97
2.17
2.15
1.48
2.64
1.84
1.89
2.00
1.84
2.20
2.68
2.20
2.12
2.42
2.02
1.74
2.42
2.39
1.56
2.32
1.95
1.95
869
905
935
913
894
939
888
911
905
884
917
924
937
930
931
932
929
915
938
939
935
945
840
916
919
943
931
823
946
937
910
910
856
826
869
910
940
913
894
939
888
911
905
906
917
924
941
935
935
939
934
932
941
937
942
945
856
939
922
949
937
823
946
943
928
914
867
826
5349
2188
4968
3656
1333
4251
1053
2221
3470
5876
4221
2203
3710
3327
3080
2269
3701
6839
2523
2311
1966
2489
4187
8784
2854
2511
1749
6129
2829
2692
1997
2958
4233
5273
35
36
37
38
39
40
41
2322
2340
2352
2358
2400
2442
2466
1.71
1.85
1.82
2.10
2.03
2.00
2.37
923
915
923
926
921
866
848
932
915
933
935
927
891
866
1959
1937
1865
1976
2296
3477
7605
42
43
44
45
46
47
48
49
50
2484
2508
2748
2844
2928
3204
3366
3516
3894
2.35
2.39
1.83
0.18
3.49
4.07
4.99
4.39
5.68
indolea
methylindole
methylindole
methylindole
dimethylindole
dimethylindole
dimethylindole
dimethylindole
trimethylindole
trimethylindole
trimethylindole
carbazolea
methylcarbazole
methylcarbazole
methylcarbazole
dimethylcarbazole
methylcarbazole
ethylcarbazole
dimethylcarbazole
dimethylcarbazole
dimethylcarbazole
dimethylcarbazole
ethylcarbazole
ethylcarbazole
dimethylcarbazole
dimethylcarbazole
dimethylcarbazole
trimethylcarbazole
dimethylcarbazole
dimethylcarbazole
trimethylcarbazole
dimethylcarbazole
trimethylcarbazole
dihydro-dimethylbenzoquinoline
trimethylcarbazole
trimethylcarbazole
trimethylcarbazole
trimethylcarbazole
trimethylcarbazole
trimethylcarbazole
dihydro-dimethylbenzoquinoline
trimethylcarbazole
trimethylcarbazole
pentamethylcarbazole
octadecenamide
dimethylphenylindole
benzocarbazole
benzocarbazole
diphenylpyridine
butylmethylphenylimidazolidinone
921
922
805
842
819
881
852
823
899
934
926
805
842
819
937
895
935
962
4010
2393
7099
4757
4450
6267
3059
6979
5973
a
tR (s)
Table 3. Compounds Tentatively Identified in the Neutral Fraction of
HGO Samples Based on the Structured Pattern within the Separation
Space and Mass Spectra Profile
carbazoles
number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
1
tR (s)
C4
2364
2412
2466
2580
2604
2634
2658
2712
2718
2760
2772
2832
C5
2580
2604
2676
2808
2982
3084
C6
2730
2766
2772
2808
2886
2898
2928
2958
3006
3012
3132
3150
3228
3300
C7
2994
3008
3216
C8
3360
3396
3450
benzocarbazoles
2
tR (s)
1.280
1.67
1.40
1.66
1.70
1.76
1.86
1.96
2.22
2.09
2.09
2.17
1.30
1.12
1.37
1.72
1.86
2.15
0.98
1.11
0.99
1.22
1.53
1.19
1.37
1.37
1.48
1.54
1.80
1.65
1.84
1.92
1.00
1.19
1.39
1.20
1.35
1.34
number
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
1
tR (s)
C1
3372
3450
3468
3504
3516
3588
3624
3696
C2
3480
3540
3612
3654
3666
3702
3708
3732
3762
3822
3834
3858
3924
C3
3798
3852
3864
3906
3936
4008
4020
4028
4074
C4
3972
4020
4044
4062
4086
4104
4158
4182
4200
4236
4248
4284
C5
4248
2
tR (s)
3.73
3.86
3.710
4.07
4.39
4.55
4.51
4.97
3.16
3.17
3.40
3.43
3.7
3.43
4.00
4.02
3.94
4.10
4.44
4.29
4.33
3.17
3.19
3.34
3.54
3.41
3.52
3.58
3.61
3.84
2.88
2.80
2.93
2.96
2.16
3.17
3.20
3.15
3.32
3.36
3.46
3.73
2.96
identified on the basis of only deconvoluted mass spectral
profiles, retention times in both dimensions, and information taken from SID structured elution patterns. These compounds are listed in Table 3.
The roof-tile effect of the alkyl-indole region (a relationship that presents homologues and isomers of compounds in
a structured pattern that resembles a roof-tile effect in the 2D
space) was not characterized when the GC GC-NPD33
was used, but the use of MS information from GC GC/
TOFMS resulted in a well-characterized structured alkylindole region, as demonstrated by its classification region in
Figure 3.
Some compounds identified in Table 2, such as dihydrodimethylbenzoquinoline and octadecenamide, were expected in the basic fraction and not in the neutral fraction. This
information is consistent with the low extraction efficiency
toward molecular class differentiation observed using different extraction techniques.15
Confirmation with pure analytical standard co-injection.
The structure of carbazole allows four possible methyl
isomers, and all of them were easily detected, as illustrated in
Figure 3B and Table 2. For ethyl carbazoles, only three of
four isomers were detected, while the other CC2 compounds
were dimethyl carbazole isomers. It is possible that other
isomers were not present in the sample because of a specific
biosynthesis process or chemical reaction.35 The structured
separation of those compounds by GC GC and identification by TOFMS will permit a detailed study on the origin
of this distribution. Another 81 compounds were tentatively
(35) Dorbon, M.; Schmitter, J. M.; Garrigues, P.; Ignatiadis, I.;
Ewald, M.; Arpino, P.; Guiochon, G. Org. Geochem. 1984, 7 (2), 111–
120.
3577
Energy Fuels 2010, 24, 3572–3580
: DOI:10.1021/ef1002364
von M€uhlen et al.
Figure 4. TID obtained with GC GC/TOFMS from a basic
fraction of a HGO sample: (A) before and (B) after classification
process. In panel B, Q represents alkyl-quinolines from C2 to C3 on
the upper left part of the TID, on the lower region of the TID,
B corresponds to alkyl-benzoquinolines from C0 to C5 and IP corresponds to indene-pyridines from C0 to C1, respectively, and DBQ
corresponds to alkyl-dibenzoquinolines from C0 to C5 to the right
part of the TID.
Identification of Compounds in the Basic Fraction. A typical GCGC/TOFMS TID for the basic fraction is presented
in Figure 4A. The presence of a PAH region in this fraction
was not as abundant as in the neutral fraction, suggesting a
more selective extraction toward PAH in the neutral fraction. The same classification procedure adopted for compounds in the neutral fraction was adapted to the basic fraction,
using the typical m/z values observed for basic compounds,
as listed in Table 1. All classification regions selected are
illustrated in Figure 4B.
The roof-tile effect observed for alkyl-quinolines, indenepyridines, alkyl-benzoquinolines, and alkyl-dibenzoquinolines
for selected ions is presented in Figure 5. Although the number
of coeluting/overlapping regions for successive homologues
was not very extensive, identifying the region of alkyl-quinolines was more challenging than for the other regions, because
for some peaks, the mass spectra did not follow the characteristic expected pattern. It means that, even when using GC GC coupled with MS, if a SIM mode were employed (e.g., with
a quadrupole MS system) or if the mass spectra were not correctly deconvoluted, a misclassification might occur. The use
of selective detectors to quantify N-containing compounds of
the basic fraction based on chemical class distribution in the
separation space would result in overquantification, in the case
of having interfering compounds in the same region. However,
the use of a TOFMS detector should facilitate correct quantification of the required chemical class.
Figure 5. SID obtained with GC GC/TOFMS from a basic fraction of a HGO sample. (A) Q represents alkyl-quinolines. (B) B
corresponds to alkyl-benzoquinolines from C0 to C5 and IP corresponds to indene-pyridines from C0 to C1, respectively. (C) DBQ
corresponds to alkyl-dibenzoquinolines from C0 to C5 to the right
section of the TID.
Compounds of the basic fraction identified through a comparison of experimental MS and commercial library MS, also
taking into consideration the molecular information from the
structured pattern of the separation space, are presented in
Table 4. A total of 90 N-containing compounds were identified
using the formerly explained criteria, and another 27 compounds were tentatively identified in that sample based on only
deconvoluted MS evaluation (Table 5). From the 90 compounds identified, 40% were alkyl-carbazoles or alkyl-indoles,
which would be expected in the neutral fraction. Most of these
compounds were observed in both fractions, but alkyl-benzocarbazoles were concentrated in the basic fraction and not in the
neutral fraction. This demonstrates that the employed neutral
and basic separation methodology was not completely selective. These findings were not so evident using only 1D GC/MS
3578
Energy Fuels 2010, 24, 3572–3580
: DOI:10.1021/ef1002364
von M€uhlen et al.
Table 4. Compounds Identified in the Basic Fraction of HGO
Samples Based on the Structured Pattern within the Separation
Space and MS Library Match
number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
1
tR (s)
750
930
942
1158
1290
1458
1524
1554
1560
1584
1614
1644
1662
1686
1704
1710
1734
1776
1800
1818
1848
1866
1872
1884
1902
1914
1920
1926
1926
1944
1956
1962
1974
1986
1998
2010
2022
2058
2058
2070
2082
2094
2100
2130
2130
2142
2154
2184
2202
2208
2208
2214
2232
2244
2250
2262
2262
2328
2340
2340
2358
2406
2424
2460
2466
2466
2466
2472
2478
2490
2508
2514
2
tR (s)
name
S
R
P
4.42
4.94
4.97
0.39
0.39
0.89
1.47
1.49
1.91
0.78
1.78
2.17
1.22
1.92
1.15
1.96
1.99
1.64
1.70
1.60
3.32
1.68
1.83
1.75
1.87
2.17
1.75
1.25
2.14
1.45
1.32
2.59
2.19
1.84
2.30
1.44
1.61
1.59
2.08
1.94
1.95
2.02
1.79
1.89
2.22
2.34
2.20
0.89
2.38
2.01
2.49
1.39
2.36
2.35
1.29
1.58
2.75
1.68
1.85
2.93
1.75
1.96
3.15
3.21
2.11
2.17
3.37
3.49
2.01
2.34
2.14
2.34
dimethylquinoline
trimethylquinoline
trimethylquinoline
indenepyridine
methylindenepyridine
methylindenepyridine
7,8-benzoquinolinea
benzoquinoline
phenanthroline
dimethylcarbazole
5,6-benzoquinolinea
carbazolea
methylbenzoquinoline
benzoquinoline
methylbenzoquinoline
benzoquinoline
benzoisoquinoline
methylbenzoquinoline
methylbenzoquinoline
methylbenzoquinoline
indenopyridinone
methylbenzoquinoline
methylbenzoquinoline
methylbenzoquinoline
methylbenzoquinoline
methylcarbazole
methylbenzoquinoline
dimethylbenzoquinoline
methylcarbazole
dimethylcarbazole
dimethylbenzoquinoline
methylcarbazole
methylbenzoquinoline
ethylcarbazole
methylbenzoquinoline
dimethylbenzoquinoline
dimethylbenzoquinoline
dimethylbenzoquinoline
phenylisoquinoline
dimethylcarbazole
dimethylcarbazole
phenylisoquinoline
dimethylcarbazole
methylphenylindole
dimethylcarbazole
phenylisoquinoline
ethylcarbazole
trimethylbenzoquinoline
dimethylcarbazole
dimethylcarbazole
phenylisoquinoline
trimethylcarbazole
dimethylcarbazole
dimethylcarbazole
trimethylbenzoquinoline
trimethylcarbazole
indeneisoquinoline
trimethylcarbazole
trimethylcarbazole
indeneisoquinoline
trimethylcarbazole
trimethylcarbazole
phenylisoquinoline
indeneisoquinoline
trimethylcarbazole
trimethylcarbazole
dibenzoquinoline
dibenzoquinoline
trimethylcarbazole
trimethylcarbazole
trimethylcarbazole
trimethylcarbazole
902
902
892
918
840
839
961
964
849
838
933
899
878
909
895
901
862
851
863
871
805
914
829
800
876
854
869
827
861
904
832
913
824
811
813
810
887
849
877
903
896
806
903
834
917
820
826
819
877
824
802
877
914
917
811
856
923
878
883
906
892
857
801
859
860
800
929
900
869
882
818
858
921
902
892
918
848
870
965
969
886
849
939
919
886
910
904
903
880
858
873
880
817
924
850
800
884
871
879
840
884
922
834
914
828
861
813
835
887
859
896
915
913
825
925
844
929
878
872
820
885
858
835
886
919
925
811
864
923
900
889
906
904
864
882
890
870
848
929
900
885
905
840
874
7344
6874
5002
7181
5340
6187
7648
6501
6690
1974
4199
4127
6300
3734
6284
5164
2300
4816
6722
6461
9014
7524
5354
6363
5173
2848
5945
5812
3111
2071
5306
4593
3439
4406
3942
6416
7730
7282
4965
2385
2067
2237
1785
6609
1709
2089
6947
3701
1743
1449
4348
2606
2592
1874
3891
1922
3653
1548
2051
3565
1729
1935
8481
4929
2210
2011
6739
3244
2265
3671
1645
1710
Table 4. Continued
number
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
a
1
tR (s)
2
2556
2646
2658
2670
2718
2772
2796
2814
2868
3054
3162
3180
3198
3276
3300
3312
3630
4602
tR (s)
name
S
R
P
3.53
2.93
3.10
3.29
3.07
3.16
3.44
3.25
3.42
3.49
3.68
3.90
3.79
3.91
3.90
4.21
3.51
2.25
dibenzoquinoline
benzocarbazole
benzocarbazole
benzocarbazole
benzocarbazole
benzocarbazole
benzocarbazole
indenequinoline
benzocarbazole
dibenzoquinoline
dibenzoquinoline
dibenzoquinoline
dibenzoquinoline
dibenzoquinoline
dibenzoquinoline
dibenzoquinoline
dimethylindenoquinoline
tribenzoquinoline
864
823
878
821
839
830
843
831
819
862
915
818
874
867
883
840
803
911
864
846
884
841
846
898
854
880
849
883
936
851
895
899
906
886
822
937
3366
3648
4536
4253
5217
2916
4482
3798
4056
7802
9797
9230
7796
9704
9666
9611
8223
5976
Confirmation with pure analytical standard co-injection.
Table 5. Compounds Tentatively Identified in the Basic Fraction of
HGO Samples Based on Structured Pattern within the Separation
Space and Mass Spectra
benzoquinolines
number
1
2
3
4
5
6
7
8
1
tR (s)
C3
2136
2160
C4
2382
2412
2460
C5
2598
2694
2862
dibenzoquinolines
2
tR (s)
0.84
1.40
0.77
0.77
0.82
0.72
0.77
1.19
number
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
1
tR (s)
C1
3198
3342
3390
3408
C2
3492
3522
3588
3636
3642
3684
C3
3744
3870
3900
3966
C4
3848
4050
4104
4140
4230
2
tR (s)
2.83
3.51
3.33
3.50
2.73
2.89
3.40
2.99
3.33
3.49
2.48
3.22
3.13
3.22
2.28
2.56
2.89
2.83
3.17
analysis, for the same kind of sample.14 The development of
quantitative and fully selective fractionation and extraction
techniques are still a challenge for N-containing compounds
in petrochemical samples. However, the use of GC GC/
TOFMS technology significantly aids the unique identification
of all respective compound classes in the sample.
A newer version of the ChromaTOF software also allows
for the classification of compounds based on the presence of
a heteroatom among identified compounds in the peak table,
such as nitrogen. This tool can reduce the time spent in
searching for N-containing compounds in a peak table with
more than 10 000 peaks, which is an important advance for
simplification of target compound class identification and is
recommended for such work in the future.
Conclusions
Speciation of N-containing compounds in an HGO sample
using GC GC/TOFMS and based on a separation strategy
3579
Energy Fuels 2010, 24, 3572–3580
: DOI:10.1021/ef1002364
1
von M€uhlen et al.
2
that incorporated a nonpolar D column phase and D polar
phase has been accomplished. In comparison to previous GC
GC-NPD studies, MS provides additional scope for molecular identification, the use of additional analytical information provided by GCGC/TOFMS over and above retention
times in 1D and 2D, and analytical standard co-injection,
including improved structured elution patterns in the separation space in the TID, the structured pattern in the separation
space with selection of specific m/z values, library MS match
factor, and characteristic deconvoluted mass spectra. Collectively, these were a key strategy to achieve successful identification after the fractionation and separation steps. It was
possible to identify or tentatively identify 228 N-containing
compounds in a HGO sample. Almost half of these components (108 compounds) were not present in the commercial
mass spectra library; however, on the basis of the abovementioned information, tentative identification of these
compounds was feasible, although it was not possible to precisely confirm their isomeric structures. With regard to 2D
columns, comparative selectivity provided by a new generation of high-temperature polar phases would be interesting to
study.
Acknowledgment. Carin von M€
uhlen thanks the Conselho
Nacional de Desenvolvimento Cientı́fico e Tecnol
ogico (CNPq),
a Brazilian governmental institution, that promotes scientific and
technological development and the Coordenac-~
ao de Aperfeic- oamento de Pessoal de Nı́vel Superior (CAPES) for Ph.D. grants.
The authors thank Petrobras for kindly providing the HGO
samples. The technical assistance of Mr. Paul Morrison is gratefully acknowledged.
3580