- Email: [email protected]
Characterization of compounds in unresolved complex mixtures (UCM) of a Mesoproterzoic shale by using GC×GC-TOFMS
Accepted Manuscript Characterization of compounds in unresolved complex mixtures (UCM) of a Mesoproterzoic shale by using GC × GC – TOFMS Shuifu Li, Jian Cao, Shouzhi Hu, Genming Luo PII:
S0264-8172(15)30040-4
DOI:
10.1016/j.marpetgeo.2015.07.019
Reference:
JMPG 2295
To appear in:
Marine and Petroleum Geology
Received Date: 28 May 2015 Revised Date:
28 June 2015
Accepted Date: 20 July 2015
Please cite this article as: Li, S., Cao, J., Hu, S., Luo, G., Characterization of compounds in unresolved complex mixtures (UCM) of a Mesoproterzoic shale by using GC × GC – TOFMS, Marine and Petroleum Geology (2015), doi: 10.1016/j.marpetgeo.2015.07.019. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Characterization of compounds in unresolved complex mixtures (UCM)
RI PT
of a Mesoproterzoic shale by using GC × GC – TOFMS
SC
Shuifu Lia*, Jian Caob*, Shouzhi Hua, Genming Luoc
M AN U
a. Key Laboratory of Tectonics and Petroleum Resources (China University of Geosciences, Wuhan), Ministry of Education, Wuhan, China 430074.
b. State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and
TE D
Engineering, Nanjing University, Nanjing 210023, China
c. State Key Laboratory of Biogeology and Environmental Geology, China University of
EP
Geosciences, Wuhan, China 430074.
AC C
* Corresponding authors,
Shuifu Li. Tel: +8618986130262. Email: [email protected] Jian Cao. Email: [email protected].
1
ACCEPTED MANUSCRIPT
ABSTRACT Unresolved complex mixtures (UCM) in shales have important implications for organic matter
RI PT
formation and diagenesis. However, their origin is not well understood, one important reason for this is lacking the knowledge of their molecular compositions. Here, using the comprehensive two-dimensional gas chromatography (GC × GC) coupled with time-of-flight mass spectrometry (TOFMS), we conduct a pilot study based on a Mesoproterozoic black shale from North China.
SC
Detailed identification of compounds was made and a possible new origin was suggested.
M AN U
Results show that the separation of UCM hydrocarbons by a reversed-phase column system (polar/non-polar) is efficient for the identification of molecular composition of UCM. The UCM in the shale is composed mainly of C11–C27 compounds, including paraffin hydrocarbons, cycloalkanes and aromatics, in particular 1–3 cyclic paraffins with a short-chain alkyl group, multi-branched isoparaffins and their homologous series, which are indicative of isomerization
TE D
of molecules intensively. This implies that the origin of the UCM might include the isomerization of organic molecules in addition to the commonly-thought microbial activities.
AC C
shales.
EP
This study improves the understanding of the geochemical compositions and origin of UCM in
Keywords:
UCM; GC × GC – TOFMS; normal/reversed phase column systems; low- to middle-molecular-weight hydrocarbons; black shales; Mesoproterozoic Xiamaling Formation; North China
2
ACCEPTED MANUSCRIPT
1. Introduction Unresolved complex mixtures (UCM), refers to the “hump” in the conventional gas chromatogram (GC) of hydrocarbon fractions in soluble organic matter and is believed to be
RI PT
unresolved due to the complex and unknown molecular compositions ( Gough and Rowland, 1990; Killops and Al-Juboori, 1990; Gough et al., 1992). However, the UCM has significant geological/geochemical implications, e.g., for biodegradation as they are widely present when
SC
the organic matter was subjected to alteration ( Rubinstein et al., 1977; Ahsan et al., 1997; Huang et al., 2003; Korkmaz et al., 2013; Xiang et al., 2015). Therefore, the study of the UCM is critical
M AN U
in organic geochemistry and related geological studies, and is challenging due to the limitation of analytical advances.
Comprehensive two-dimensional gas chromatography (GC × GC) is a powerful analytical tool developed in the 1990s for separating complex mixtures (Liu and Phillips, 1991; Phillips
TE D
and Beens, 1999; Mao et al., 2009). When coupled with time-of-flight mass spectrometry (TOFMS), which is a total-ion-scanning analytical technique with increased sensitivity and higher acquisition rates than quadrupole mass spectrometry (Wang et al., 2014), the method can
EP
be used to effectively separate and identify individual compounds with high resolution and thus is one of the analytical highlights in organic geochemistry during recent years ( Adahchour et al.,
AC C
2006; von Mühlen et al., 2006; Li et al., 2008). Therefore, the GC × GC – TOFMS provides a possible means to characterize the molecular composition of UCM. For example, Ventura et al. (2008) satisfactory separated the UCM extracted from Late Archean sediments. However, the analysis was conducted only under a normal (non-polar/polar) phase column system without the reversed (polar/non-polar) phase column system. This compressed the aliphatic compounds in the sediments into a narrow
3
ACCEPTED MANUSCRIPT
extension on the second polar column, and thus resulted in a relatively ineffective use of the second dimensional retention space. Tran et al. (2010) analyzed biodegraded oils using a reversed column configuration, and obtained better resolution of the aliphatic compounds than
RI PT
under the normal column phase system; these compounds constitute the bulk of UCM. However, little detailed identification of compounds has been performed as their research focus was not the
issues is detailed identification of the compounds in UCM.
SC
identification. Therefore, the study of UCM in organic matters is still challenging. One of the key
Here, to further improve the understanding of this issue, as UCM is widely present in shales,
M AN U
we conducted a case study of a Mesoproterozoic shale collected in North China by using GC × GC – TOFMS. The reason for the sample selection is both scientifically and industrially. Scientifically, the shale sequences have been believed to be rare as they are still relatively low-mature (oil window) with old age (Precambrian), and thus have important scientific
TE D
implications. Industrially, the shales are potential hydrocarbon source rocks and thus have critical significance for the hydrocarbon exploration in the Proterozoic of North China (Xie et al., 2013). Both the normal and the reversed phase column systems of GC × GC – TOFMS were used for
EP
comparison. Detailed identification of compounds was performed. Based on the geochemical results, we further address the origin of the UCM in the black shale. This can add to the
AC C
understanding of the basic scientific issue of the origin of the UCM.
2. Sample and methods 2.1. Sample
The black shale sample in this study was collected from the Mesoproterozoic Xiamaling Formation. The sampling point is at the Zhaojiashan outcrop section in Huailai County, North
4
ACCEPTED MANUSCRIPT
China (N: 40°28'38.92'', E: 115°23'19.8'', H: 881 m). This set of black shales, as of scientific and industrial significance, has received much research attention (Wang and Simoneit, 1995; Gao et al., 2008; Xie et al., 2013). UCM were commonly identified in the shales, but its composition
RI PT
and origin have not been sufficiently known (Luo et al., 2015). The total organic carbon (TOC) content and δ13Corg of the shale sample are 3.37 wt.% and -34.1‰ relative to PDB, respectively. 2.2. Methods
SC
2.2.1. Extraction and separation
As the sample was collected from an outcrop section, to minimize the effects of surface
M AN U
weathering and recent contamination, weathered surface material on the sample was totally removed by cutting and the sample was thoroughly cleaned using distilled water. Then, the shale sample was finely powdered and then Soxhlet extracted with dichloromethane for 72 h, and subsequently separated into hydrocarbons and NSO fractions by an activated silica gel column
TE D
(120 °C overnight). The saturated fraction was collected using n-hexane as an eluent (Li et al., 2012). Finally, the saturated fraction was rotary evaporated and then dried under a continuous low flow of N2.
EP
2.2.2. Gas chromatography- mass spectrometry (GC-MS)
AC C
The saturated fraction was analyzed with a full scan mode (m/z 50−550) using an Agilent 6890N gas chromatograph coupled with 5973 mass spectrum (GC-MS). The GC was fitted with a DB-5MS capillary column (60 m × 0.25 mm × 0.25 µm). The sample was injected in splitless mode of an injector temperature of 310°C. The GC oven temperature program was held at 70 °C for 0.5 min and increased to 300 °C at 3 °C/min and held isothermally for 30 min. 2.2.3. GC × GC - TOFMS The GC × GC system consists of an Agilent 7890 gas chromatograph and cold/hot double 5
ACCEPTED MANUSCRIPT
vent modulator, equipped with Agilent autosampler. The time-of-flight mass spectrometer is a Pegasus 4D (Leco Corp., U.S.), and the software is ChromaTOF (Leco Corp., U.S.). The GC × GC column set in normal and reversed phase systems follows that of Li et al.
RI PT
(2012). Briefly, the primary GC oven for the normal phase system was programmed from 80 °C (0.2 min) to 300 °C (15 min) at 2.0 °C/min, and from 100 °C (2 min) to 300 °C (7 min) at
1.5 °C/min for the reversed-phase system. The secondary oven temperature program was 5 °C
SC
higher than that of the primary oven . The modulator temperature was 30 °C above the
temperature of the primary GC oven temperature for both the two column sets. The modulation
M AN U
period for the normal system was 6 s, with a 1.3 s hot pulse, and was 7.0 s with a 2.0 s hot pulse for the reversed-phase column system. The inlet temperatures for the normal and reversed column sets were 310 °C and 300 °C, respectively. Helium was the carrier gas at a flow rate of 1.5 ml/min and 1.0 ml/min for the normal and reversed column systems, respectively. The
TE D
transfer line temperature to the mass spectrometer is 280 °C.
The ionization voltage and the detector voltage were set to 70 eV and 1475 V, respectively, and the TOF ion source temperature was 240 °C. The mass spectrum acquisition frequency of
EP
TOFMS was 100 spectra/s, and the mass range for acquisition was m/z 55−550. Chroma TOF Version 4.33 was used for data analysis and only peaks with S/N > 500 were
AC C
characterized. Peak identification was performed using mass spectral library NIST05 and by the comparison of mass spectra and retention time in literatures (Wang, 1993).
3. Results and discussion
3.1. General geochemical characteristics of UCM in the total ion chromatogram (TIC) GC–MS analysis of the saturated fraction of the black shale sample displays a big UCM
6
ACCEPTED MANUSCRIPT
hump with low-molecular-weight compounds C11 to C17 in the TIC (Figure 1). The position of this distinct UCM spans in the range of n-C11–n-C27, and the constituents forming the UCM were not resolved by GC–MS.
RI PT
In contrast, the separation and identification of these unresolved mixtures have increased a lot by the analysis of GC × GC–TOFMS, especially under the reversed column system (Figures 2 and 3). In the TIC using the normal-phase column system (Figure 2), monocyclic, bicyclic and
SC
tricyclic alkylcycloalkanes of low- to middle-molecular-weight (the main part of the saturated hydrocarbon fraction of the UCM) could hardly be distinguished as they co-elute to form a
M AN U
hump.
Comparatively, in the TIC analyzed by the reversed-phase column system (Figure 3), similar to the results obtained under the normal-phase column system, tetracyclo-alkanes or alkanes with more rings co-elute with monocyclic aromatics on the high-molecular-weight end to
TE D
a certain extent. However, the reversed-phase column system provides improved resolution of individual saturated hydrocarbons. Although the range of first-dimensional rention time with reversed-phase column system is smaller than that of normal-phase column system, the elution
EP
on the second-dimensional column by the reversed-phase column system are substantially longer than that using the normal-phase column system (Figures 2 and 3). This is demonstrated by the
AC C
second-dimensional position of non-polar compounds, such as normal alkanes (< n-C23), which occurs from 1.39 s to 6.68 s retention time of the second-dimensional column (Figure 3). This greater time range increases the separation and resolution of low- to middle-molecular-weight compounds in the reversed-phase column system. In summary, the reversed-phase column system improves the separation and identification of low- to middle-molecular-weight hydrocarbons.
7
ACCEPTED MANUSCRIPT
3.2. Detailed geochemical characterization of compounds in UCM Based on the above results, it appears that the reversed-phase column system has special advantages in analyzing the UCM by GC × GC – TOFMS. As such, we undertake the analysis by
RI PT
the reversed-phase system with continuous extraction from m/z 185 to m/z 198 (Figures 4 and 5), to obtain a detailed identification of compounds in the UCM. These fourteen different ions are consistent with the mass of CH2 (14) and include m/z 191, and can reduce the signal interference
SC
of normal alkanes.
Results show that the morphological characteristics of a UCM extracted using different
M AN U
fragment ions varies markedly and the saturated and aromatic hydrocarbons appear concurrently after m/z 189. As the size of the fragment ions increases, the aromatics showing on the contour plot do not change notably, yet different types of saturated hydrocarbons can be observed for different ions (Figure 4). Ion chromatograms show that m/z 189, m/z 191 and m/z 193 are most
TE D
distinguishable for the tricyclic, bicyclic and monocyclic alkanes, respectively. This implies that a relatively large number of UCM hydrocarbon monomers can be isolated and identified. The chromatography – mass spectrometry lattice spectrum obtained using m/z 191 shows that the
EP
UCM is composed of three clearly separated regions: region a primarily containing bicyclic alkanes, region b primarily containing monocyclic alkyl benzene and bicyclic aromatic
AC C
naphthenes, and region c primarily containing bicyclic and tricyclic aromatics and polycyclic alkyl aromatic hydrocarbons as well as some sulfur-containing compounds and oxygen-containing compounds (Figure 5). The UCM consists mainly of C11–C27 hydrocarbons including alkanes (straight-chain and branched with very low contents comparable to the other compounds), cycloalkanes and aromatic naphthenes (monocyclic, bicyclic), aromatics (monocyclic benzene, bicyclic
8
ACCEPTED MANUSCRIPT
naphthalene and biphenyl, and their homologues), and other compounds. To compare individual compounds in the analyzed UCM by normal- and reversed-phase column systems, m/z 113, m/z 84 and m/z 137 were used to extract paraffin hydrocarbons,
RI PT
monocyclic alkanes and bicyclic alkanes, respectively. This can avoid the influence of other fragment ions. Results show the differences in the one-dimensional and second-dimensional retention time among the corresponding C12–C14 compounds (Figure 6, A & B inside the red box)
SC
between the reversed- and normal-phase column systems. This illustrates the advantages of the reversed-phase column system in the separation of isoalkanes and cycloalkanes of low- to
M AN U
middle-molecular-weight, which help to understand the isomerization of UCM (see section 3.4). In the range of C12–C14, eight compounds were identified: 2-ethyldecahydro-naphthalene, hexylcyclohexane, 1-ethyldecahydro-naphthalene, tridecane, 2-propyldecahydro-naphthalene, 1-propyldecahydro-naphthalene, heptylcycohexane and tetradecane (Table 1). As illustrated in
TE D
Figure 6 (A & B), due to the difference in the polarity of the one-dimensional column, the peak elution order using the reversed-phase column system is different from that using the normal-phase column system (mass spectra of each compound in Figure 6 A and 6B as shown in
EP
Figures 7 and 8, respectively). Using the normal-phase column system, some alkyl decalin compounds cannot be separated well; for example, compounds e and f elute together. However,
AC C
these two compounds are well separated under the reverse-phase column system, and their peak shapes are much better compared to that under the normal-phase column system. Table 1 shows the maximum differences in the one-dimensional and second-dimensional retention time between compounds a, b, c and d. In the normal-phase column system, the maximum difference in the first-dimensional retention time is only 54 s whereas that in the reversed-phase column system is 105 s (nearly double). Similarly, the maximum difference in the
9
ACCEPTED MANUSCRIPT
first-dimensional retention time using the normal-phase column system is only 0.21 s, whereas it is 1.12 s in the reverse-phase column system, a nearly six-fold difference. To examine the retention time of two compounds f and h (f: bicyclic alkanes, h: paraffin
RI PT
hydrocarbons) in the normal- and reversed-phase column systems, the differences in their
first-dimensional retention time are 54 s and 14 s, respectively. Moreover, the differences in the
column systems, respectively, showing a large discrepancy.
SC
second-dimensional retention time are 0.27 s and 1.32 s for the normal- and reverse-phase
As the carbon number of the compounds increases, the differences in the
M AN U
second-dimensional retention time increase in the reverse-phase column system. The difference between the retention time of compounds c and d is not as large as that between compounds f and h. In addition, data on the TIC reveal that the range of the second-dimensional retention time across the main body of UCM using the normal-phase column system is only 2.71 s and is 5.29 s
TE D
using the reverse-phase column system (Figures 2 and 3). Therefore, the reverse-phase column system is especially efficient in the separation of saturated hydrocarbons with low or no polarity. This advantage has been widely shown and discussed in previous research (Li et al., 2015b). The
EP
results of this study provide a new case.
3.3. Advantage of reversed-phase column system to analyze UCM using GC × GC –
AC C
TOFMS
Based on the results of this study, it is showed that the reversed-phase column system is superior to the normal-phase column system in the separation of UCM components using GC × GC – TOFMS, especially those low- to middle-molecular-weight compounds (Figures 2 and 3). This advantage has been widely shown in previous research (Li et al., 2015b). The results of this study provide a new case.
10
ACCEPTED MANUSCRIPT
As universally known, the GC × GC – TOFMS method has two experimental systems including normal (non-polar/polar) and reversed (polar/non-polar) ones (Adahchour et al., 2004; Tran et al., 2006; Hu et al., 2014). Considering that the vast majority of hydrocarbons in organic
RI PT
matter (especially normal to light crude oil) are non-polar or weakly polar (Peters et al., 2005a), the normal-phase column system has been commonly used with the first column being non-polar, while the reversed-phase column system has received relatively less attention (Ventura et al.,
SC
2011; Oliveira et al., 2012a; Ventura et al., 2012; Soares et al., 2013; Zhu et al., 2013). Analytical results show that the separation capacity of normal-phase columns becomes superior as the
M AN U
molecular weight and polarity of the hydrocarbons increase, and the retention time in the second column increases nearly exponentially (Silva et al., 2011; Oliveira et al., 2012b; Casilli et al., 2014; Kiepper et al., 2014). Therefore, in the GC × GC – TOFMS analysis the normal-phase column system is quite effective for the separation of hydrocarbons with high molecular weights
TE D
and certain polarities.
However, the normal-phase column system is far less efficient for the separation of non-polar hydrocarbons than polar compounds because the second column is polar in nature; this
EP
is especially true for non-polar compounds of low- to middle-molecular-weight such as paraffin hydrocarbons, iso-paraffins, naphthenes and bicyclic alkanes (Tran et al., 2006; Tran et al., 2010;
AC C
Hu et al., 2014). These compounds are crucial to the understanding of the geochemistry of organic matter. To complement this, the reversed-phase column system has attracted more and more attention. As the second-dimensional column of the system is non-polar, it can improve the resolution and increase the use of the second-dimensional separation space for the non-polar compounds (Tran et al., 2006; Hu et al., 2014). As a consequence, the reversed-phase column system is expected to effectively separate low- to middle-molecular-weight hydrocarbons that
11
ACCEPTED MANUSCRIPT
have small differences in polarity. For example, Tran et al. (2010) used the reversed-phase column system to analyze UCM in crude oils and achieved satisfactory separation results, illustrating the advantage and latest advance of this approach. This was further shown in this
RI PT
study. The reversed-phase column system is of particular significance in the separation and identification of low- to middle-molecular-weight hydrocarbons (Figures 2 and 3). 3.4. Origin of UCM
SC
The UCM has been widely been observed in oils, pyrobitumens and reservoir/source rock
M AN U
extracts with important geological/geochemical implications (Gough et al., 1992; Frysinger et al., 2003; Peacock et al., 2007; Scarlett et al., 2007; Wu et al., 2012). UCM in oils, pyrobitumens and reservoir rock extracts is commonly ascribed to the biodegradation of oils (Gough et al., 1992; Peacock et al., 2007; Scarlett et al., 2007; Zhang et al., 2014), while in source rocks it is most
TE D
likely related to microbial activities (Cao et al., 2008; Pawlowska et al., 2013; Craig et al., 2013). Thus, it seem that the UCM exists almost in all oils and rock extracts regardless biodegradation or not. Once n-alkanes dominate in compositions, the UCM is depressed; otherwise, it becomes
EP
eminent. Alternatively, Ventura et al. (2012) suggested an interesting mechanism for generation
AC C
during the early stages of hydrothermal petroleum formation based on its occurrence. In this study, the sample is very unique. It has been exposed to surface for several hundred million years and the loss of n-alkanes in extracts can be caused by several possible reasons, including hydrocarbon loss, oxidation, biodegradation, microbial activity and hydrothermal impact. As for hydrocarbon loss and/or oxidation, the low-molecular-weight hydrocarbons tend to be lost in comparison with high-molecular-weight hydrocarbons (Peters et al., 2005b).
12
ACCEPTED MANUSCRIPT
However, abundant low-molecular-weight normal alkanes (n-C11 to n-C17) have been observed in this study (Figure 1). Thus, these possibilities for the formation of UCM in this study can be
RI PT
excluded. As for the hydrothermal impact, the bitumen commonly contains abundant low- and
high-molecular-weight n-alkanes (Simoneit et al., 2004; Ventura et al., 2008; Ventura et al.,
SC
2012). However, the distribution of n-alkanes in this study is dominated by n-C11 to n-C17 with
M AN U
the absence of high-molecular-weight n-alkanes (Figure 1). In addition, no hydrothermal evidence has been discovered from the shale sample (Luo et al., 2015). Thus, the possibility of hydrothermal impact on the formation of UCM in this study can be excluded. As for the biodegradation, there is two sub-possibilities: oil biodegradation and shale
TE D
biodegradation. In terms of oil biodegradation, the shale in this study is not a reservoir rock and there are no oil contaminants (Luo et al., 2015). In addition, if this UCM was formed by migrated oils, such a big hump as in this study (Figure 1) would commonly coexist with
EP
25-horpanes (Larter et al., 2012; Li et al., 2015a). Furthermore, normal alkanes in the oil,
AC C
especially low- and moderate-molecular-weight compounds would disappear prior to the presence of UCM during the oil biodegradation (Robson and Rowland, 1988). These characteristics indicative of oil biodegradation, however, have not been detected in the sample. Thus, the UCM in this shale could not be caused by biodegradation of migrated hydrocarbons. With respect to the shale biodegradation, it differs significantly from oil biodegradation in reservoir and 25-norhopanes are not necessarily involved and commonly related to microbial activities (Cao et al., 2008; Pawlowska et al., 2013). Under such conditions, compounds 13
ACCEPTED MANUSCRIPT
indicative of microbes should be detected, e.g., hopanes (Peters et al., 2005b). In this study, the chromatographic profile for the shale exhibits a coexistence of a significant UCM hump and
RI PT
n-alkanes (Figure 1), and steranes and hopanes exhibit no discernible peaks in conventional one-dimensional GC-MS chromatograms. However, hopanes ranging from C27 to C35 were
detected by GC-MS-MS (Luo et al., 2015), suggesting the presence of microbial activity. In
SC
addition, according to the compositions of normal alkane, hopanes, steranes and the compound
M AN U
specific carbon isotopic compositions of n-alkanes, bacteria were one primary biotic precursors (Luo et al., 2015). Thus, microbial activities in the shale during diagenisis seem to be one possible candidate for the occurrence of big UCM in this study (Blumenberg et al., 2012; Pawlowska et al., 2013).
TE D
In addition, based on the GC × GC – TOFMS results gained in this study, we have another possible interpretation. In the studied shale, the aliphatic fraction of UCM consists mainly of 1–3 cyclic paraffins with short chain alkyl groups, multi-branched isoalkanes and their homologues,
EP
which are indicative of isomerization of molecules intensively. This implies that the significant
AC C
UCM might be triggered by enhanced isomerization of all the organic molecules present over the burial of the shale rather than the direct result of microbial activities alone. This possible origin needs further investigation.
4. Conclusions Based on a case study of Mesoproterozoic Xiamaling black shale, sample from North China, we report the detailed geochemical compositions of the UCM present and propose a possible
14
ACCEPTED MANUSCRIPT
new origin, which needs more studies. A comparative study using both normal- and reversed-column systems of GC × GC – TOFMS shows that the reversed-column system has
low- to middle-molecular-weight compounds.
RI PT
unique advantages for the separation and compositional identification of the UCM, especially
The UCM in this study is composed mainly of C10–C25 hydrocarbons including paraffin hydrocarbons (straight chain and branched), cycloalkanes (monocyclic, bicyclic, tricyclic) and
SC
aromatic hydrocarbons (monocyclic benzene, bicyclic naphthalene and biphenyl series). The aliphatic fractions of the UCM consist mainly of 1–3 cyclic paraffins with short chain alkyl
M AN U
groups, multi-branched isoalkanes and their homologues.
The origin of the UCM in the studied sample might include the isomerization of organic molecules present over the burial of the Xiamaling shale besides the microbial activities.
TE D
Acknowledgements
We thank Drs. Thomas Gentzis and Zhirong Zhang and the other two anonymous reviewers
EP
for their detailed reviews and comments, which help to improve the article. This study was jointly supported by the “973” project (Grant Nos. 2012CB214804 and 2014CB239105) and
AC C
National Natural Science Foundation of China (Grant No. 41273052).
References
Adahchour, M., Beens, J., Vreuls, R., Brinkman, U., 2006. Recent developments in comprehensive two-dimensional gas chromatography (GC×GC) III. Applications for
15
ACCEPTED MANUSCRIPT
petrochemicals and organohalogens. Trends in Analytical Chemistry 25, 726-741. Adahchour, M., Beens, J., Vreuls, R.J.J., Batenburg, A.M., Brinkman, U.A.T., 2004.
RI PT
Comprehensive two-dimensional gas chromatography of complex samples by using a ‘reversed-type’ column combination: application to food analysis. Journal of Chromatography
SC
A 1054, 47-55.
Ahsan, A., Karlsen, D.A., Patience, R.L., 1997. Petroleum biodegradation in the Tertiary
M AN U
reservoirs of the North Sea. Marine and Petroleum Geology 14, 55-64.
Blumenberg, M., Thiel, V., Riegel, W., Kah, L.C., Reitner, J., 2012. Biomarkers of black shales formed by microbial mats, Late Mesoproterozoic (1.1Ga) Taoudeni Basin, Mauritania.
TE D
Precambrian Research 196-197, 113-127.
Cao, J., Hu, K., Wang, K., Bian, L., Liu, Y., Yang, S., Wang, L., Chen, Y., 2008. Possible origin of 25-norhopanes in Jurassic organic-poor mudstones from the northern Qaidam Basin (NW
EP
China). Organic Geochemistry 39, 1058-1065.
AC C
Casilli, A., Silva, R.C., Laakia, J., Oliveira, C.J.F., Ferreira, A.A., Loureiro, M.R.B., Azevedo, D.A., Aquino Neto, F.R., 2014. High resolution molecular organic geochemistry assessment of Brazilian lacustrine crude oils. Organic Geochemistry 68, 61-70. Craig, J., Biffi, U., Galimberti, R.F., Ghori, K.A.R., Gorter, J.D., Hakhoo, N., Le Heron, D.P., Thurow, J., Vecoli, M., 2013. The palaeobiology and geochemistry of Precambrian hydrocarbon source rocks. Marine and Petroleum Geology 40, 1-47.
16
ACCEPTED MANUSCRIPT
Frysinger, G.S., Gaines, R.B., Xu, L., Reddy, C.M., 2003. Resolving the Unresolved Complex Mixture in Petroleum-Contaminated Sediments. Environmental Science & Technology 37,
RI PT
1653-1662. Gao, L., Zhang, C., Shi, X., Song, B., Wang, Z., Liu, Y., 2008. Mesoproterozoic age for Xiamaling Formation in North China Plate indicated by zircon SHRIMP dating. Chinese
SC
Science Bulletin 53, 2665-2671.
M AN U
Gough, M.A., Rhead, M.M., Rowland, S.J., 1992. Biodegradation studies of unresolved complex mixtures of hydrocarbons model UCM hydrocarbons and the aliphatic UCM. Organic Geochemistry 18, 17-22.
Gough, M.A., Rowland, S.J., 1990. Characterization of unresolved complex mixtures of
TE D
hydrocarbons in petroleum. Nature 344, 648-650. Hu, S.Z., Li, S.F., Cao, J., Zhang, D.M., Ma, J., He, S., Wang, X.L., Wu, M., 2014. A comparison
EP
of normal and reversed phase columns in oil analysis by comprehensive two-dimensional gas
AC C
chromatography with time-of-flight mass spectrometry. Petroleum Science and Technology 32, 565-574.
Huang, H., Jin, G., Lin, C., Zheng, Y., 2003. Origin of an unusual heavy oil from the Baiyinchagan depression, Erlian basin, northern China. Marine and Petroleum Geology 20, 1-12. Kiepper, A.P., Casilli, A., Azevedo, D.A., 2014. Depositional paleoenvironment of Brazilian
17
ACCEPTED MANUSCRIPT
crude oils from unusual biomarkers revealed using comprehensive two dimensional gas chromatography coupled to time of flight mass spectrometry. Organic Geochemistry 70,
RI PT
62-75. Killops, S.D., Al-Juboori, M.A.H.A., 1990. Characterisation of the unresolved complex mixture (UCM) in the gas chromatograms of biodegraded petroleums. Organic Geochemistry 15,
SC
147-160.
M AN U
Korkmaz, S., Kara-Gülbay, R., İztan, Y.H., 2013. Organic geochemistry of the Lower Cretaceous black shales and oil seep in the Sinop Basin, Northern Turkey: An oil–source rock correlation study. Marine and Petroleum Geology 43, 272-283.
Larter, S., Huang, H., Adams, J., Bennett, B., Snowdon, L.R., 2012. A practical biodegradation
66-76.
TE D
scale for use in reservoir geochemical studies of biodegraded oils. Organic Geochemistry 45,
EP
Li, M., Zhang, S., Jiang, C., Zhu, G., Fowler, M., Achal, S., Milovic, M., Robinson, R., Larter, S.,
AC C
2008. Two-dimensional gas chromatograms as fingerprints of sour gas-associated oils. Organic Geochemistry 39, 1144-1149. Li, N., Huang, H., Jiang, W., Wu, T., Sun, J., 2015a. Biodegradation of 25-norhopanes in a Liaohe Basin (NE China) oil reservoir. Organic Geochemistry 78, 33-43. Li, S., Cao, J., Hu, S., 2015b. Analyzing hydrocarbon fractions in crude oils by two-dimensional gas chromatography/time-of-flight mass spectrometry under reversed-phase column system.
18
ACCEPTED MANUSCRIPT
Fuel 158, 191-199. Li, S., Hu, S., Cao, J., Wu, M., Zhang, D., 2012. Diamondoid characterization in condensate by
RI PT
comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry: the Junggar Basin of northwest China. International Journal of Molecular Sciences 13,
SC
11399-11410.
Liu, Z.Y., Phillips, J.B., 1991. Comprehensive 2-dimensional gas-chromatography using an
M AN U
on-column thermal modulator interface. Journal of Chromatographic Science 29, 227-231. Luo, G., Hallmann, C., Xie, S., Ruan, X., Summons, R.E., 2015. Comparative microbial diversity and redox environments of black shale and stromatolite facies in the Mesoproterozoic
TE D
Xiamaling Formation. Geochimica et Cosmochimica Acta 151, 150-167. Mao, D., Weghe, H.V.D., Lookman, R., Vanermen, G., Brucker, N.D., Diels, L., 2009. Resolving the unresolved complex mixture in motor oils using high-performance liquid chromatography
EP
followed by comprehensive two-dimensional gas chromatography. Fuel 88, 312-318.
AC C
Oliveira, C.R., Ferreira, A.A., Oliveira, C.J.F., Azevedo, D.A., Santos Neto, E.V., Aquino Neto, F.R., 2012a. Biomarkers in crude oil revealed by comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry: Depositional paleoenvironment proxies. Organic Geochemistry 46, 154-164. Oliveira, C.R., Oliveira, C.J.F., Ferreira, A.A., Azevedo, D.A., Aquino Neto, F.R., 2012b. Characterization of aromatic steroids and hopanoids in marine and lacustrine crude oils using
19
ACCEPTED MANUSCRIPT
comprehensive two dimensional gas chromatography coupled to time-of-flight mass spectrometry (GCxGC-TOFMS). Organic Geochemistry 53, 131-136.
RI PT
Pawlowska, M.M., Butterfield, N.J., Brocks, J.J., 2013. Lipid taphonomy in the Proterozoic and the effect of microbial mats on biomarker preservation. Geology 41, 103-106.
SC
Peacock, E.E., Hampson, G.R., Nelson, R.K., Xu, L., Frysinger, G.S., Gaines, R.B., Farrington, J.W., Tripp, B.W., Reddy, C.M., 2007. The 1974 spill of the Bouchard 65 oil barge: petroleum
M AN U
hydrocarbons persist in Winsor Cove salt marsh sediments. Marine Pollution Bulletin 54, 214-225.
Peters, K.E., Walters, C.C., Moldowan, J.M., 2005a. Biomarkers and isotopes in the environment and human history, Biomarker Guide, Second ed. Cambridge University Press, New York, pp.
TE D
1-474.
Peters, K.E., Walters, C.C., Moldowan, J.M., 2005b. Biomarkers and isotopes in petroleum
EP
systems and earth history, Biomarker Guide, Second ed. Cambridge University Press, New
AC C
York, pp. 475-1132.
Phillips, J.B., Beens, J., 1999. Comprehensive two-dimensional gas chromatography: a hyphenated method with strong coupling between the two dimensions. Journal of Chromatography A 856, 331-347. Robson, J.N., Rowland, S.J., 1988. Biodegradation of highly branched isoprenoid hydrocarbons: A possible explanation of sedimentary abundance. Organic Geochemistry 13, 691-695.
20
ACCEPTED MANUSCRIPT
Rubinstein, I., Strausz, O.P., Spyckerelle, C., Crawford, R.J., Westlake, D.W.S., 1977. The origin of the oil sand bitumens of Alberta a chemical and microbiological simulation study.
RI PT
Geochimica et Cosmochimica Acta 41, 1341-1353. Scarlett, A., Galloway, T.S., Rowland, S.J., 2007. Chronic toxicity of unresolved complex mixtures (UCM) of hydrocarbons in marine sediments. Journal of Soils and Sediments 7,
SC
200-206.
M AN U
Silva, R.S.F., Aguiar, H.G.M., Rangel, M.D., Azevedo, D.A., Aquino Neto, F.R., 2011. Comprehensive two-dimensional gas chromatography with time of flight mass spectrometry applied to biomarker analysis of oils from Colombia. Fuel 90, 2694-2699. Simoneit, B.R.T., Lein, A.Y., Peresypkin, V.I., Osipov, G.A., 2004. Composition and origin of
TE D
hydrothermal petroleum and associated lipids in the sulfide deposits of the Rainbow field (Mid-Atlantic Ridge at 36°N). Geochimica et Cosmochimica Acta 68, 2275-2294.
EP
Soares, R.F., Pereira, R., Silva, R.S.F., Mogollon, L., Azevedo, D.A., 2013. Comprehensive
AC C
two-dimensional gas chromatography coupled to time of flight mass spectrometry: new biomarker parameter proposition for the characterization of biodegraded oil. Journal of the Brazilian Chemical Society 24, 1570-1581. Tran, T.C., Logan, G.A., Grosjean, E., Harynuk, J., Ryan, D., Marriott, P., 2006. Comparison of column phase configurations for comprehensive two dimensional gas chromatographic analysis of crude oil and bitumen. Organic Geochemistry 37, 1190-1194.
21
ACCEPTED MANUSCRIPT
Tran, T.C., Logan, G.A., Grosjean, E., Ryan, D., Marriott, P.J., 2010. Use of comprehensive two-dimensional
gas
chromatography
time-of-flight
mass
spectrometry
for
the
Geochimica et Cosmochimica Acta 74, 6468-6484.
RI PT
characterization of biodegradation and unresolved complex mixtures in petroleum.
Ventura, G.T., Hall, G.J., Nelson, R.K., Frysinger, G.S., Raghuraman, B., Pomerantz, A.E.,
SC
Mullins, O.C., Reddy, C.M., 2011. Analysis of petroleum compositional similarity using
M AN U
multiway principal components analysis (MPCA) with comprehensive two-dimensional gas chromatographic data. Journal of Chromatography A 1218, 2584-2592. Ventura, G.T., Kenig, F., Reddy, C.M., Frysinger, G.S., Nelson, R.K., Mooy, B.V., Gaines, R.B., 2008. Analysis of unresolved complex mixtures of hydrocarbons extracted from Late Archean
TE D
sediments by comprehensive two-dimensional gas chromatography (GC×GC). Organic Geochemistry 39, 846-867.
EP
Ventura, G.T., Simoneit, B.R.T., Nelson, R.K., Reddy, C.M., 2012. The composition, origin and fate of complex mixtures in the maltene fractions of hydrothermal petroleum assessed by
AC C
comprehensive two-dimensional gas chromatography. Organic Geochemistry 45, 48-65. von Mühlen, C., Zini, C.A., Caramão, E.B., Marriott, P.J., 2006. Applications of comprehensive two-dimensional gas chromatography to the characterization of petrochemical and related samples. Journal of Chromatography A 1105, 39-50. Wang, G., Cheng, B., Wang, T.G., Simoneit, B.R.T., Shi, S., Wang, P., 2014. Monoterpanes as
22
ACCEPTED MANUSCRIPT
molecular indicators to diagnose depositional environments for source rocks of crude oils and condensates. Organic Geochemistry 72, 59-68.
RI PT
Wang, P., 1993. The mass spectrum criterion of petroleum biomarkers. Petroleum Industry Press, Beijing.
SC
Wang, T.G., Simoneit, B.R.T., 1995. Tricyclic terpanes in Precambrian bituminous sandstone from the eastern Yanshan region, North China. Chemical Geology 120, 155-170.
M AN U
Wu, L., Liao, Y., Fang, Y., Geng, A., 2012. The study on the source of the oil seeps and bitumens in the Tianjingshan structure of the northern Longmen Mountain structure of Sichuan Basin, China. Marine and Petroleum Geology 37, 147-161.
TE D
Xiang, B., Zhou, N., Ma, W., Wu, M., Cao, J., 2015. Multiple-stage migration and accumulation of Permian lacustrine mixed oils in the central Junggar Basin (NW China). Marine and Petroleum Geology 59, 187-201.
EP
Xie, L., Sun, Y., Yang, Z., Chen, J., Jiang, A., Zhang, Y., Deng, C., 2013. Evaluation of
AC C
hydrocarbon generation of the Xiamaling Formation shale in Zhangjiakou and its significance to the petroleum geology in North China. Science China Earth Sciences 56, 444-452. Zhang, Z., Hu, W., Song, X., Zhang, C., Zhang, Q., Jin, J., 2014. A comparison of results from two different flash pyrolysis methods on a solid bitumen sample. Organic Geochemistry 69, 36-41. Zhu, G., Wang, H., Weng, N., Huang, H., Liang, H., Ma, S., 2013. Use of comprehensive 23
ACCEPTED MANUSCRIPT
two-dimensional gas chromatography for the characterization of ultra-deep condensate from
AC C
EP
TE D
M AN U
SC
RI PT
the Bohai Bay Basin, China. Organic Geochemistry 63, 8-17.
24
ACCEPTED MANUSCRIPT
Table and Figure Captions
from the Mesoproterozoic Xiamaling shale by GC × GC – TOFMS.
RI PT
Table 1. Retention time for C12 – C14 paraffin hydrocarbons, mono- and bicyclic alkanes detected
SC
Figure 1. TIC chromatogram of the extracted saturated fraction of the Mesoproterozoic
M AN U
Xiamaling shale analyzed by GC – MS.
Figure 2. GC × GC – TOFMS TIC chromatogram of UCM analyzed by the normal-phase column system.
column system.
TE D
Figure 3. GC × GC – TOFMS TIC chromatogram of UCM analyzed by the reversed-phase
EP
Figure 4. Characteristics of UCM with different fragment ions analyzed by the GC × GC – TOFMS reversed-phase system (m/z 185 to 198). Abbreviations, Par: Paraffins; MAk:
AC C
Monocyclic Alkanes; BAk: Bicyclic Alkanes; TAk: Tricyclic Alkanes; MAr: Monocyclic Aromatics; CAr: Cycloalkyl Aromatics; BAr: Bicyclic Aromatics.
Figure 5. Characterization of UCM by the GC × GC – TOFMS reversed-phase column system. (A) m/z 191 mass chromatogram. (B) Structures of individual compounds in UCM corresponding to circles a, b and c in Figure A.
25
ACCEPTED MANUSCRIPT
Figure 6. GC × GC – TOFMS summed mass chromatograms showing the paraffins, mono-cyclic and bicyclic alkanes of UCM. (A) Fragment ion m/z 113+84×3+137×5 by normal-phase column system. (B) Fragment ion m/z 113+84×3+137×5 by reversed-phase column system. Their mass
RI PT
spectra of individual compounds a, b, c, d, e, f, g, and h in Figures A and B are shown in Figures 7 and 8, respectively, and their names were identified and listed in Table 1.
SC
Figure 7. Mass spectra of compounds a, b, c, d, e, f, g and h in Figure 6A.
AC C
EP
TE D
M AN U
Figure 8. Mass spectra of compounds a, b, c, d, e, f, g and h in Figure 6B.
26
ACCEPTED MANUSCRIPT
Table 1. Retention time for C12 – C14 paraffin hydrocarbons, mono-cyclic alkanes and bicyclic alkanes in the analysis of the Mesoproterozoic Xiamaling shale sample by GC × GC – TOFMS.
Normal-phase
Molecular Compound name
a
1082
2-Ethyldecahydro-Naphthalene
C12H22
166
1622, 1.780
b
1116
Hexylcyclohexane
C12H24
168
1646, 1.690
c
1145
1-Ethyldecahydro-Naphthalene
C12H22
166
1658, 1.830
d
1170
Tridecane
C13H28
184
1676, 1.520
1.830-1.520=0.31 s
e&f
1777
C13H24
180
1982, 1.840
Difference in the first-dimensional retention time between compounds f and h:
C13H26
182
2024, 1.750
2036-1982=54 s
weight
M AN U
2-Propyldecahydro-Naphthalene 1-Propyldecahydro-Naphthalene g
h
1887
Tetradecane
C14H30
Maximum difference in the first-dimensional retention time among the four compounds: 1676-1622=54 s
Maximum difference in the second-dimensional retention time among the four compounds:
198
2036, 1.570
Difference in the second-dimensional retention time between compounds f and h: 1.840-1.570=0.27 s
C12H24
168
741, 3.110
Tridecane
C13H28
184
783, 4.020
1029
2-Ethyldecahydro-Naphthalene
C12H22
166
804, 2.900
Maximum difference in the second-dimensional retention time among the four compounds:
c
1112
1-Ethyldecahydro-Naphthalene
C12H22
166
846, 2.940
4.020-2.900=1.12 s
g
1564
Heptylcycohexane
C13H26
182
1021, 3.810
e
1675
2-Propyldecahydro-Naphthalene
C13H24
180
1063, 3.520
h
1706
Tetradecane
C14H30
198
1077, 4.780
Difference in the second-dimensional retention time between compounds f and h:
f
1735
1-Propyldecahydro-Naphthalene
C13H24
180
1091, 3.460
4.780-3.460=1.32 s
889
d
997
a
Hexylcyclohexane
TE D
b
column
AC C
system
Heptylcycohexane
EP
Reversed-phase
1859
Difference in retention time
RI PT
Formula
column system
1st D & 2nd D time (s)
Peak No.
Label
SC
Type
Maximum difference in the first-dimensional retention time among the four compounds: 846-741=105 s
Difference in the first-dimensional retention time between compounds f and h: 1091-1077=14 s
27
ACCEPTED MANUSCRIPT
Figure 1 nC14
nC15
abundance
nC16 nC12
nC23 nC17 nC18nC19
nC25 nC27
TIC
nC21
RI PT
nC13
nC11
UCM
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
EP
TE D
M AN U
Time (min)
AC C
10.00
SC
nC10
28
ACCEPTED MANUSCRIPT
Bicyclic Aromatics
Cycloalkyl Aromatics
RI PT
Figure 2
Monocyclic Aromatics UCM
Tricyclic Alkanes
Bicyclic Alkanes Monocyclic Alkanes Paraffins
AC C
EP
TE D
M AN U
SC
Naphthalene
29
ACCEPTED MANUSCRIPT
RI PT
Figure 3
Paraffins
nC21
UCM
C20, m/z 82, WM=280
SC
Monocyclic Alkanes
Bicyclic Alkanes
C19
Tricyclic Alkanes
C 19
117 63 60
77
91 102
80
100
146
128 120
140
128 63
87 80
102 100
120
Bicyclic Aromatics
AC C
EP
TE D
60
74
M AN U
Monocyclic Aromatics
Cycloalkyl Aromatics
30
ACCEPTED MANUSCRIPT
Figure 4
Par
Par
MAk BAk TAk MAr CAr BAr
MAk BAk TAk MAr CAr BAr
Par MAk BAk TAk MAr CAr BAr
Par
TE D
MAk BAk TAk MAr CAr BAr
Par
MAk BAk TAk MAr CAr BAr
Par
Par
MAk BAk TAk MAr CAr BAr
MAk BAk TAk MAr CAr BAr
M AN U
Par MAk BAk TAk MAr CAr BAr
SC
Par MAk BAk TAk MAr CAr BAr
RI PT
Par MAk BAk TAk MAr CAr BAr
Par
Par
MAk BAk TAk MAr CAr BAr
MAk BAk TAk MAr CAr BAr
Par
Par
MAk BAk TAk MAr CAr BAr
MAk BAk TAk MAr CAr BAr
AC C
EP
Par
MAk BAk TAk MAr CAr BAr
31
ACCEPTED MANUSCRIPT
Figure 5 79
67
109 135
100
150
100
200
150
149
247
191 200
100
250
150
191
247
177 200
290
211 240 100
250
150
200
C21 TT
C20 TT
A
81
123
95
149
220
150
81
123
95
191
300
191
95
68
250
123
RI PT
95
67
82
C19 TT
163
276
243
100
C18 TT
150
200
250
67
95
67
a
95
123
123 163
67 135 121 149
b 91 105
100
150
133
161
100
150
c
200
60
77 80
129
169
1000
155
190
91 105 65 77
100 120 140 160 180 200
a
60
80
143
190
100 120 140 160 180 200
b
82 97
130
183
100
150
150
200
262
250
226 213
200
63
89
115
100
195 179
252 223
143 150
200
250
c
AC C
EP
TE D
B
100
191 177 206
149
250
M AN U
65
200
206
119 147
191
SC
81
233 248
32
ACCEPTED MANUSCRIPT
Figure 6
RI PT
A Aromatic Hydrocarbon
b
138
d C13H28
C12H26
B
e f g h
C14H30
222
SC
c
a
208
C16H34
M AN U
152
194
180
166
C15H32
C17H36
C17H36
C18H38
C18H38
C16H34
TE D
C15H32
C14H30
h
C13H28
d
208
194
b
ef
EP
C12H26
g
222
ac
Aromatic Hydrocarbon
AC C
166
180
152
138
33
ACCEPTED MANUSCRIPT
Figure 7 Peak True - sample "20110109-alk1-Sat-2D:1", peak 1082 Peak True - sample "20110109-alk1-Sat-2D:1", peak 1777 , at 1622 , 1.780 sec , sec , at 1982 , 1.840 sec , sec
a
67
e&f
81
1000
95
67
137
95
166
109
RI PT
81
1000
137
180
60 80 100 120 140 160 60 80 100 120 140 160 180 Peak True - sample "20110109-alk1-Sat-2D:1", peak 1116 Peak True - sample "20110109-alk1-Sat-2D:1", peak 1777 , at 1646 , 1.690 sec , sec , at 1982 , 1.840 sec , sec
b 67 168
67
e&f
81
1000
83
SC
1000
95
137
180
M AN U
60 80 100 120 140 160 60 80 100 120 140 160 180 Peak True - sample "20110109-alk1-Sat-2D:1", peak 1145 Peak True - sample "20110109-alk1-Sat-2D:1", peak 1859 , at 1658 , 1.830 sec , sec , at 2024 , 1.750 sec , sec
c
81
1000
67
g
1000
95
83
137
67
166
109 123
182
98
60 80 100 120 140 160 60 80 100 120 140 160 180 Peak True - sample "20110109-alk1-Sat-2D:1", peak 1170 Peak True - sample "20110109-alk1-Sat-2D:1", peak 1887 , at 1676 , 1.520 sec , sec , at 2036 , 1.570 sec , sec 1000 71 85 98 112 80
100
120
h
1000 71 85 98 112
184
140
160
180
60
80
154
198
100 120 140 160 180 200
AC C
EP
60
TE D
d
34
ACCEPTED MANUSCRIPT
Figure 8
RI PT
Peak True - sample "20110104-alk1-2D:1", peak 889, at 7 Peak True - sample "20110104-alk1-2D:1", peak 1564, at 41 , 3.110 sec , sec 1021 , 3.810 sec , sec
g
b 1000
1000
83
83
67
69
168
98
97
125
154
182
d
1000
1000
81
137
M AN U
67
154
e
95
71 83 98 113
SC
60 80 100 120 140 160 60 80 100 120 140 160 180 Peak True - sample "20110104-alk1-2D:1", peak 997, at 7 Peak True - sample "20110104-alk1-2D:1", peak 1675, at 83 , 4.020 sec , sec 1063 , 3.520 sec , sec
184
180
123
60 80 100 120 140 160 180 60 80 100 120 140 160 180 Peak True - sample "20110104-alk1-2D:1", peak 1029, at Peak True - sample "20110104-alk1-2D:1", peak 1706, at 804 , 2.900 sec , sec 1077 , 4.780 sec , sec 81
1000
h
a
95
1000
67 137 110 123
71
166 151
85
99
126
198
155
TE D
60 80 100 120 140 160 60 80 100 120 140 160 180 200 Peak True - sample "20110104-alk1-2D:1", peak 1112, at Peak True - sample "20110104-alk1-2D:1", peak 1735, at 1091 , 3.460 sec , sec 846 , 2.940 sec , sec
c
81
1000
95
67
137
EP
80
100
120
140
160
137 180
107 60
80
100
120
140
160
180
AC C
60
95
67
166
109 123
f
81
1000
35
ACCEPTED MANUSCRIPT Highlights: UCM present in the Mesoproterozoic Xiamaling shale, North China. Detailed C10–C25 compounds were identified in UCM by GC × GC - TOFMS.
RI PT
Results by reversed-phase column system are better than normal-phase column system.
AC C
EP
TE D
M AN U
SC
UCM was formed by isomerization of organic molecules besides microbial activities.
S0264-8172(15)30040-4
DOI:
10.1016/j.marpetgeo.2015.07.019
Reference:
JMPG 2295
To appear in:
Marine and Petroleum Geology
Received Date: 28 May 2015 Revised Date:
28 June 2015
Accepted Date: 20 July 2015
Please cite this article as: Li, S., Cao, J., Hu, S., Luo, G., Characterization of compounds in unresolved complex mixtures (UCM) of a Mesoproterzoic shale by using GC × GC – TOFMS, Marine and Petroleum Geology (2015), doi: 10.1016/j.marpetgeo.2015.07.019. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Characterization of compounds in unresolved complex mixtures (UCM)
RI PT
of a Mesoproterzoic shale by using GC × GC – TOFMS
SC
Shuifu Lia*, Jian Caob*, Shouzhi Hua, Genming Luoc
M AN U
a. Key Laboratory of Tectonics and Petroleum Resources (China University of Geosciences, Wuhan), Ministry of Education, Wuhan, China 430074.
b. State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and
TE D
Engineering, Nanjing University, Nanjing 210023, China
c. State Key Laboratory of Biogeology and Environmental Geology, China University of
EP
Geosciences, Wuhan, China 430074.
AC C
* Corresponding authors,
Shuifu Li. Tel: +8618986130262. Email: [email protected] Jian Cao. Email: [email protected].
1
ACCEPTED MANUSCRIPT
ABSTRACT Unresolved complex mixtures (UCM) in shales have important implications for organic matter
RI PT
formation and diagenesis. However, their origin is not well understood, one important reason for this is lacking the knowledge of their molecular compositions. Here, using the comprehensive two-dimensional gas chromatography (GC × GC) coupled with time-of-flight mass spectrometry (TOFMS), we conduct a pilot study based on a Mesoproterozoic black shale from North China.
SC
Detailed identification of compounds was made and a possible new origin was suggested.
M AN U
Results show that the separation of UCM hydrocarbons by a reversed-phase column system (polar/non-polar) is efficient for the identification of molecular composition of UCM. The UCM in the shale is composed mainly of C11–C27 compounds, including paraffin hydrocarbons, cycloalkanes and aromatics, in particular 1–3 cyclic paraffins with a short-chain alkyl group, multi-branched isoparaffins and their homologous series, which are indicative of isomerization
TE D
of molecules intensively. This implies that the origin of the UCM might include the isomerization of organic molecules in addition to the commonly-thought microbial activities.
AC C
shales.
EP
This study improves the understanding of the geochemical compositions and origin of UCM in
Keywords:
UCM; GC × GC – TOFMS; normal/reversed phase column systems; low- to middle-molecular-weight hydrocarbons; black shales; Mesoproterozoic Xiamaling Formation; North China
2
ACCEPTED MANUSCRIPT
1. Introduction Unresolved complex mixtures (UCM), refers to the “hump” in the conventional gas chromatogram (GC) of hydrocarbon fractions in soluble organic matter and is believed to be
RI PT
unresolved due to the complex and unknown molecular compositions ( Gough and Rowland, 1990; Killops and Al-Juboori, 1990; Gough et al., 1992). However, the UCM has significant geological/geochemical implications, e.g., for biodegradation as they are widely present when
SC
the organic matter was subjected to alteration ( Rubinstein et al., 1977; Ahsan et al., 1997; Huang et al., 2003; Korkmaz et al., 2013; Xiang et al., 2015). Therefore, the study of the UCM is critical
M AN U
in organic geochemistry and related geological studies, and is challenging due to the limitation of analytical advances.
Comprehensive two-dimensional gas chromatography (GC × GC) is a powerful analytical tool developed in the 1990s for separating complex mixtures (Liu and Phillips, 1991; Phillips
TE D
and Beens, 1999; Mao et al., 2009). When coupled with time-of-flight mass spectrometry (TOFMS), which is a total-ion-scanning analytical technique with increased sensitivity and higher acquisition rates than quadrupole mass spectrometry (Wang et al., 2014), the method can
EP
be used to effectively separate and identify individual compounds with high resolution and thus is one of the analytical highlights in organic geochemistry during recent years ( Adahchour et al.,
AC C
2006; von Mühlen et al., 2006; Li et al., 2008). Therefore, the GC × GC – TOFMS provides a possible means to characterize the molecular composition of UCM. For example, Ventura et al. (2008) satisfactory separated the UCM extracted from Late Archean sediments. However, the analysis was conducted only under a normal (non-polar/polar) phase column system without the reversed (polar/non-polar) phase column system. This compressed the aliphatic compounds in the sediments into a narrow
3
ACCEPTED MANUSCRIPT
extension on the second polar column, and thus resulted in a relatively ineffective use of the second dimensional retention space. Tran et al. (2010) analyzed biodegraded oils using a reversed column configuration, and obtained better resolution of the aliphatic compounds than
RI PT
under the normal column phase system; these compounds constitute the bulk of UCM. However, little detailed identification of compounds has been performed as their research focus was not the
issues is detailed identification of the compounds in UCM.
SC
identification. Therefore, the study of UCM in organic matters is still challenging. One of the key
Here, to further improve the understanding of this issue, as UCM is widely present in shales,
M AN U
we conducted a case study of a Mesoproterozoic shale collected in North China by using GC × GC – TOFMS. The reason for the sample selection is both scientifically and industrially. Scientifically, the shale sequences have been believed to be rare as they are still relatively low-mature (oil window) with old age (Precambrian), and thus have important scientific
TE D
implications. Industrially, the shales are potential hydrocarbon source rocks and thus have critical significance for the hydrocarbon exploration in the Proterozoic of North China (Xie et al., 2013). Both the normal and the reversed phase column systems of GC × GC – TOFMS were used for
EP
comparison. Detailed identification of compounds was performed. Based on the geochemical results, we further address the origin of the UCM in the black shale. This can add to the
AC C
understanding of the basic scientific issue of the origin of the UCM.
2. Sample and methods 2.1. Sample
The black shale sample in this study was collected from the Mesoproterozoic Xiamaling Formation. The sampling point is at the Zhaojiashan outcrop section in Huailai County, North
4
ACCEPTED MANUSCRIPT
China (N: 40°28'38.92'', E: 115°23'19.8'', H: 881 m). This set of black shales, as of scientific and industrial significance, has received much research attention (Wang and Simoneit, 1995; Gao et al., 2008; Xie et al., 2013). UCM were commonly identified in the shales, but its composition
RI PT
and origin have not been sufficiently known (Luo et al., 2015). The total organic carbon (TOC) content and δ13Corg of the shale sample are 3.37 wt.% and -34.1‰ relative to PDB, respectively. 2.2. Methods
SC
2.2.1. Extraction and separation
As the sample was collected from an outcrop section, to minimize the effects of surface
M AN U
weathering and recent contamination, weathered surface material on the sample was totally removed by cutting and the sample was thoroughly cleaned using distilled water. Then, the shale sample was finely powdered and then Soxhlet extracted with dichloromethane for 72 h, and subsequently separated into hydrocarbons and NSO fractions by an activated silica gel column
TE D
(120 °C overnight). The saturated fraction was collected using n-hexane as an eluent (Li et al., 2012). Finally, the saturated fraction was rotary evaporated and then dried under a continuous low flow of N2.
EP
2.2.2. Gas chromatography- mass spectrometry (GC-MS)
AC C
The saturated fraction was analyzed with a full scan mode (m/z 50−550) using an Agilent 6890N gas chromatograph coupled with 5973 mass spectrum (GC-MS). The GC was fitted with a DB-5MS capillary column (60 m × 0.25 mm × 0.25 µm). The sample was injected in splitless mode of an injector temperature of 310°C. The GC oven temperature program was held at 70 °C for 0.5 min and increased to 300 °C at 3 °C/min and held isothermally for 30 min. 2.2.3. GC × GC - TOFMS The GC × GC system consists of an Agilent 7890 gas chromatograph and cold/hot double 5
ACCEPTED MANUSCRIPT
vent modulator, equipped with Agilent autosampler. The time-of-flight mass spectrometer is a Pegasus 4D (Leco Corp., U.S.), and the software is ChromaTOF (Leco Corp., U.S.). The GC × GC column set in normal and reversed phase systems follows that of Li et al.
RI PT
(2012). Briefly, the primary GC oven for the normal phase system was programmed from 80 °C (0.2 min) to 300 °C (15 min) at 2.0 °C/min, and from 100 °C (2 min) to 300 °C (7 min) at
1.5 °C/min for the reversed-phase system. The secondary oven temperature program was 5 °C
SC
higher than that of the primary oven . The modulator temperature was 30 °C above the
temperature of the primary GC oven temperature for both the two column sets. The modulation
M AN U
period for the normal system was 6 s, with a 1.3 s hot pulse, and was 7.0 s with a 2.0 s hot pulse for the reversed-phase column system. The inlet temperatures for the normal and reversed column sets were 310 °C and 300 °C, respectively. Helium was the carrier gas at a flow rate of 1.5 ml/min and 1.0 ml/min for the normal and reversed column systems, respectively. The
TE D
transfer line temperature to the mass spectrometer is 280 °C.
The ionization voltage and the detector voltage were set to 70 eV and 1475 V, respectively, and the TOF ion source temperature was 240 °C. The mass spectrum acquisition frequency of
EP
TOFMS was 100 spectra/s, and the mass range for acquisition was m/z 55−550. Chroma TOF Version 4.33 was used for data analysis and only peaks with S/N > 500 were
AC C
characterized. Peak identification was performed using mass spectral library NIST05 and by the comparison of mass spectra and retention time in literatures (Wang, 1993).
3. Results and discussion
3.1. General geochemical characteristics of UCM in the total ion chromatogram (TIC) GC–MS analysis of the saturated fraction of the black shale sample displays a big UCM
6
ACCEPTED MANUSCRIPT
hump with low-molecular-weight compounds C11 to C17 in the TIC (Figure 1). The position of this distinct UCM spans in the range of n-C11–n-C27, and the constituents forming the UCM were not resolved by GC–MS.
RI PT
In contrast, the separation and identification of these unresolved mixtures have increased a lot by the analysis of GC × GC–TOFMS, especially under the reversed column system (Figures 2 and 3). In the TIC using the normal-phase column system (Figure 2), monocyclic, bicyclic and
SC
tricyclic alkylcycloalkanes of low- to middle-molecular-weight (the main part of the saturated hydrocarbon fraction of the UCM) could hardly be distinguished as they co-elute to form a
M AN U
hump.
Comparatively, in the TIC analyzed by the reversed-phase column system (Figure 3), similar to the results obtained under the normal-phase column system, tetracyclo-alkanes or alkanes with more rings co-elute with monocyclic aromatics on the high-molecular-weight end to
TE D
a certain extent. However, the reversed-phase column system provides improved resolution of individual saturated hydrocarbons. Although the range of first-dimensional rention time with reversed-phase column system is smaller than that of normal-phase column system, the elution
EP
on the second-dimensional column by the reversed-phase column system are substantially longer than that using the normal-phase column system (Figures 2 and 3). This is demonstrated by the
AC C
second-dimensional position of non-polar compounds, such as normal alkanes (< n-C23), which occurs from 1.39 s to 6.68 s retention time of the second-dimensional column (Figure 3). This greater time range increases the separation and resolution of low- to middle-molecular-weight compounds in the reversed-phase column system. In summary, the reversed-phase column system improves the separation and identification of low- to middle-molecular-weight hydrocarbons.
7
ACCEPTED MANUSCRIPT
3.2. Detailed geochemical characterization of compounds in UCM Based on the above results, it appears that the reversed-phase column system has special advantages in analyzing the UCM by GC × GC – TOFMS. As such, we undertake the analysis by
RI PT
the reversed-phase system with continuous extraction from m/z 185 to m/z 198 (Figures 4 and 5), to obtain a detailed identification of compounds in the UCM. These fourteen different ions are consistent with the mass of CH2 (14) and include m/z 191, and can reduce the signal interference
SC
of normal alkanes.
Results show that the morphological characteristics of a UCM extracted using different
M AN U
fragment ions varies markedly and the saturated and aromatic hydrocarbons appear concurrently after m/z 189. As the size of the fragment ions increases, the aromatics showing on the contour plot do not change notably, yet different types of saturated hydrocarbons can be observed for different ions (Figure 4). Ion chromatograms show that m/z 189, m/z 191 and m/z 193 are most
TE D
distinguishable for the tricyclic, bicyclic and monocyclic alkanes, respectively. This implies that a relatively large number of UCM hydrocarbon monomers can be isolated and identified. The chromatography – mass spectrometry lattice spectrum obtained using m/z 191 shows that the
EP
UCM is composed of three clearly separated regions: region a primarily containing bicyclic alkanes, region b primarily containing monocyclic alkyl benzene and bicyclic aromatic
AC C
naphthenes, and region c primarily containing bicyclic and tricyclic aromatics and polycyclic alkyl aromatic hydrocarbons as well as some sulfur-containing compounds and oxygen-containing compounds (Figure 5). The UCM consists mainly of C11–C27 hydrocarbons including alkanes (straight-chain and branched with very low contents comparable to the other compounds), cycloalkanes and aromatic naphthenes (monocyclic, bicyclic), aromatics (monocyclic benzene, bicyclic
8
ACCEPTED MANUSCRIPT
naphthalene and biphenyl, and their homologues), and other compounds. To compare individual compounds in the analyzed UCM by normal- and reversed-phase column systems, m/z 113, m/z 84 and m/z 137 were used to extract paraffin hydrocarbons,
RI PT
monocyclic alkanes and bicyclic alkanes, respectively. This can avoid the influence of other fragment ions. Results show the differences in the one-dimensional and second-dimensional retention time among the corresponding C12–C14 compounds (Figure 6, A & B inside the red box)
SC
between the reversed- and normal-phase column systems. This illustrates the advantages of the reversed-phase column system in the separation of isoalkanes and cycloalkanes of low- to
M AN U
middle-molecular-weight, which help to understand the isomerization of UCM (see section 3.4). In the range of C12–C14, eight compounds were identified: 2-ethyldecahydro-naphthalene, hexylcyclohexane, 1-ethyldecahydro-naphthalene, tridecane, 2-propyldecahydro-naphthalene, 1-propyldecahydro-naphthalene, heptylcycohexane and tetradecane (Table 1). As illustrated in
TE D
Figure 6 (A & B), due to the difference in the polarity of the one-dimensional column, the peak elution order using the reversed-phase column system is different from that using the normal-phase column system (mass spectra of each compound in Figure 6 A and 6B as shown in
EP
Figures 7 and 8, respectively). Using the normal-phase column system, some alkyl decalin compounds cannot be separated well; for example, compounds e and f elute together. However,
AC C
these two compounds are well separated under the reverse-phase column system, and their peak shapes are much better compared to that under the normal-phase column system. Table 1 shows the maximum differences in the one-dimensional and second-dimensional retention time between compounds a, b, c and d. In the normal-phase column system, the maximum difference in the first-dimensional retention time is only 54 s whereas that in the reversed-phase column system is 105 s (nearly double). Similarly, the maximum difference in the
9
ACCEPTED MANUSCRIPT
first-dimensional retention time using the normal-phase column system is only 0.21 s, whereas it is 1.12 s in the reverse-phase column system, a nearly six-fold difference. To examine the retention time of two compounds f and h (f: bicyclic alkanes, h: paraffin
RI PT
hydrocarbons) in the normal- and reversed-phase column systems, the differences in their
first-dimensional retention time are 54 s and 14 s, respectively. Moreover, the differences in the
column systems, respectively, showing a large discrepancy.
SC
second-dimensional retention time are 0.27 s and 1.32 s for the normal- and reverse-phase
As the carbon number of the compounds increases, the differences in the
M AN U
second-dimensional retention time increase in the reverse-phase column system. The difference between the retention time of compounds c and d is not as large as that between compounds f and h. In addition, data on the TIC reveal that the range of the second-dimensional retention time across the main body of UCM using the normal-phase column system is only 2.71 s and is 5.29 s
TE D
using the reverse-phase column system (Figures 2 and 3). Therefore, the reverse-phase column system is especially efficient in the separation of saturated hydrocarbons with low or no polarity. This advantage has been widely shown and discussed in previous research (Li et al., 2015b). The
EP
results of this study provide a new case.
3.3. Advantage of reversed-phase column system to analyze UCM using GC × GC –
AC C
TOFMS
Based on the results of this study, it is showed that the reversed-phase column system is superior to the normal-phase column system in the separation of UCM components using GC × GC – TOFMS, especially those low- to middle-molecular-weight compounds (Figures 2 and 3). This advantage has been widely shown in previous research (Li et al., 2015b). The results of this study provide a new case.
10
ACCEPTED MANUSCRIPT
As universally known, the GC × GC – TOFMS method has two experimental systems including normal (non-polar/polar) and reversed (polar/non-polar) ones (Adahchour et al., 2004; Tran et al., 2006; Hu et al., 2014). Considering that the vast majority of hydrocarbons in organic
RI PT
matter (especially normal to light crude oil) are non-polar or weakly polar (Peters et al., 2005a), the normal-phase column system has been commonly used with the first column being non-polar, while the reversed-phase column system has received relatively less attention (Ventura et al.,
SC
2011; Oliveira et al., 2012a; Ventura et al., 2012; Soares et al., 2013; Zhu et al., 2013). Analytical results show that the separation capacity of normal-phase columns becomes superior as the
M AN U
molecular weight and polarity of the hydrocarbons increase, and the retention time in the second column increases nearly exponentially (Silva et al., 2011; Oliveira et al., 2012b; Casilli et al., 2014; Kiepper et al., 2014). Therefore, in the GC × GC – TOFMS analysis the normal-phase column system is quite effective for the separation of hydrocarbons with high molecular weights
TE D
and certain polarities.
However, the normal-phase column system is far less efficient for the separation of non-polar hydrocarbons than polar compounds because the second column is polar in nature; this
EP
is especially true for non-polar compounds of low- to middle-molecular-weight such as paraffin hydrocarbons, iso-paraffins, naphthenes and bicyclic alkanes (Tran et al., 2006; Tran et al., 2010;
AC C
Hu et al., 2014). These compounds are crucial to the understanding of the geochemistry of organic matter. To complement this, the reversed-phase column system has attracted more and more attention. As the second-dimensional column of the system is non-polar, it can improve the resolution and increase the use of the second-dimensional separation space for the non-polar compounds (Tran et al., 2006; Hu et al., 2014). As a consequence, the reversed-phase column system is expected to effectively separate low- to middle-molecular-weight hydrocarbons that
11
ACCEPTED MANUSCRIPT
have small differences in polarity. For example, Tran et al. (2010) used the reversed-phase column system to analyze UCM in crude oils and achieved satisfactory separation results, illustrating the advantage and latest advance of this approach. This was further shown in this
RI PT
study. The reversed-phase column system is of particular significance in the separation and identification of low- to middle-molecular-weight hydrocarbons (Figures 2 and 3). 3.4. Origin of UCM
SC
The UCM has been widely been observed in oils, pyrobitumens and reservoir/source rock
M AN U
extracts with important geological/geochemical implications (Gough et al., 1992; Frysinger et al., 2003; Peacock et al., 2007; Scarlett et al., 2007; Wu et al., 2012). UCM in oils, pyrobitumens and reservoir rock extracts is commonly ascribed to the biodegradation of oils (Gough et al., 1992; Peacock et al., 2007; Scarlett et al., 2007; Zhang et al., 2014), while in source rocks it is most
TE D
likely related to microbial activities (Cao et al., 2008; Pawlowska et al., 2013; Craig et al., 2013). Thus, it seem that the UCM exists almost in all oils and rock extracts regardless biodegradation or not. Once n-alkanes dominate in compositions, the UCM is depressed; otherwise, it becomes
EP
eminent. Alternatively, Ventura et al. (2012) suggested an interesting mechanism for generation
AC C
during the early stages of hydrothermal petroleum formation based on its occurrence. In this study, the sample is very unique. It has been exposed to surface for several hundred million years and the loss of n-alkanes in extracts can be caused by several possible reasons, including hydrocarbon loss, oxidation, biodegradation, microbial activity and hydrothermal impact. As for hydrocarbon loss and/or oxidation, the low-molecular-weight hydrocarbons tend to be lost in comparison with high-molecular-weight hydrocarbons (Peters et al., 2005b).
12
ACCEPTED MANUSCRIPT
However, abundant low-molecular-weight normal alkanes (n-C11 to n-C17) have been observed in this study (Figure 1). Thus, these possibilities for the formation of UCM in this study can be
RI PT
excluded. As for the hydrothermal impact, the bitumen commonly contains abundant low- and
high-molecular-weight n-alkanes (Simoneit et al., 2004; Ventura et al., 2008; Ventura et al.,
SC
2012). However, the distribution of n-alkanes in this study is dominated by n-C11 to n-C17 with
M AN U
the absence of high-molecular-weight n-alkanes (Figure 1). In addition, no hydrothermal evidence has been discovered from the shale sample (Luo et al., 2015). Thus, the possibility of hydrothermal impact on the formation of UCM in this study can be excluded. As for the biodegradation, there is two sub-possibilities: oil biodegradation and shale
TE D
biodegradation. In terms of oil biodegradation, the shale in this study is not a reservoir rock and there are no oil contaminants (Luo et al., 2015). In addition, if this UCM was formed by migrated oils, such a big hump as in this study (Figure 1) would commonly coexist with
EP
25-horpanes (Larter et al., 2012; Li et al., 2015a). Furthermore, normal alkanes in the oil,
AC C
especially low- and moderate-molecular-weight compounds would disappear prior to the presence of UCM during the oil biodegradation (Robson and Rowland, 1988). These characteristics indicative of oil biodegradation, however, have not been detected in the sample. Thus, the UCM in this shale could not be caused by biodegradation of migrated hydrocarbons. With respect to the shale biodegradation, it differs significantly from oil biodegradation in reservoir and 25-norhopanes are not necessarily involved and commonly related to microbial activities (Cao et al., 2008; Pawlowska et al., 2013). Under such conditions, compounds 13
ACCEPTED MANUSCRIPT
indicative of microbes should be detected, e.g., hopanes (Peters et al., 2005b). In this study, the chromatographic profile for the shale exhibits a coexistence of a significant UCM hump and
RI PT
n-alkanes (Figure 1), and steranes and hopanes exhibit no discernible peaks in conventional one-dimensional GC-MS chromatograms. However, hopanes ranging from C27 to C35 were
detected by GC-MS-MS (Luo et al., 2015), suggesting the presence of microbial activity. In
SC
addition, according to the compositions of normal alkane, hopanes, steranes and the compound
M AN U
specific carbon isotopic compositions of n-alkanes, bacteria were one primary biotic precursors (Luo et al., 2015). Thus, microbial activities in the shale during diagenisis seem to be one possible candidate for the occurrence of big UCM in this study (Blumenberg et al., 2012; Pawlowska et al., 2013).
TE D
In addition, based on the GC × GC – TOFMS results gained in this study, we have another possible interpretation. In the studied shale, the aliphatic fraction of UCM consists mainly of 1–3 cyclic paraffins with short chain alkyl groups, multi-branched isoalkanes and their homologues,
EP
which are indicative of isomerization of molecules intensively. This implies that the significant
AC C
UCM might be triggered by enhanced isomerization of all the organic molecules present over the burial of the shale rather than the direct result of microbial activities alone. This possible origin needs further investigation.
4. Conclusions Based on a case study of Mesoproterozoic Xiamaling black shale, sample from North China, we report the detailed geochemical compositions of the UCM present and propose a possible
14
ACCEPTED MANUSCRIPT
new origin, which needs more studies. A comparative study using both normal- and reversed-column systems of GC × GC – TOFMS shows that the reversed-column system has
low- to middle-molecular-weight compounds.
RI PT
unique advantages for the separation and compositional identification of the UCM, especially
The UCM in this study is composed mainly of C10–C25 hydrocarbons including paraffin hydrocarbons (straight chain and branched), cycloalkanes (monocyclic, bicyclic, tricyclic) and
SC
aromatic hydrocarbons (monocyclic benzene, bicyclic naphthalene and biphenyl series). The aliphatic fractions of the UCM consist mainly of 1–3 cyclic paraffins with short chain alkyl
M AN U
groups, multi-branched isoalkanes and their homologues.
The origin of the UCM in the studied sample might include the isomerization of organic molecules present over the burial of the Xiamaling shale besides the microbial activities.
TE D
Acknowledgements
We thank Drs. Thomas Gentzis and Zhirong Zhang and the other two anonymous reviewers
EP
for their detailed reviews and comments, which help to improve the article. This study was jointly supported by the “973” project (Grant Nos. 2012CB214804 and 2014CB239105) and
AC C
National Natural Science Foundation of China (Grant No. 41273052).
References
Adahchour, M., Beens, J., Vreuls, R., Brinkman, U., 2006. Recent developments in comprehensive two-dimensional gas chromatography (GC×GC) III. Applications for
15
ACCEPTED MANUSCRIPT
petrochemicals and organohalogens. Trends in Analytical Chemistry 25, 726-741. Adahchour, M., Beens, J., Vreuls, R.J.J., Batenburg, A.M., Brinkman, U.A.T., 2004.
RI PT
Comprehensive two-dimensional gas chromatography of complex samples by using a ‘reversed-type’ column combination: application to food analysis. Journal of Chromatography
SC
A 1054, 47-55.
Ahsan, A., Karlsen, D.A., Patience, R.L., 1997. Petroleum biodegradation in the Tertiary
M AN U
reservoirs of the North Sea. Marine and Petroleum Geology 14, 55-64.
Blumenberg, M., Thiel, V., Riegel, W., Kah, L.C., Reitner, J., 2012. Biomarkers of black shales formed by microbial mats, Late Mesoproterozoic (1.1Ga) Taoudeni Basin, Mauritania.
TE D
Precambrian Research 196-197, 113-127.
Cao, J., Hu, K., Wang, K., Bian, L., Liu, Y., Yang, S., Wang, L., Chen, Y., 2008. Possible origin of 25-norhopanes in Jurassic organic-poor mudstones from the northern Qaidam Basin (NW
EP
China). Organic Geochemistry 39, 1058-1065.
AC C
Casilli, A., Silva, R.C., Laakia, J., Oliveira, C.J.F., Ferreira, A.A., Loureiro, M.R.B., Azevedo, D.A., Aquino Neto, F.R., 2014. High resolution molecular organic geochemistry assessment of Brazilian lacustrine crude oils. Organic Geochemistry 68, 61-70. Craig, J., Biffi, U., Galimberti, R.F., Ghori, K.A.R., Gorter, J.D., Hakhoo, N., Le Heron, D.P., Thurow, J., Vecoli, M., 2013. The palaeobiology and geochemistry of Precambrian hydrocarbon source rocks. Marine and Petroleum Geology 40, 1-47.
16
ACCEPTED MANUSCRIPT
Frysinger, G.S., Gaines, R.B., Xu, L., Reddy, C.M., 2003. Resolving the Unresolved Complex Mixture in Petroleum-Contaminated Sediments. Environmental Science & Technology 37,
RI PT
1653-1662. Gao, L., Zhang, C., Shi, X., Song, B., Wang, Z., Liu, Y., 2008. Mesoproterozoic age for Xiamaling Formation in North China Plate indicated by zircon SHRIMP dating. Chinese
SC
Science Bulletin 53, 2665-2671.
M AN U
Gough, M.A., Rhead, M.M., Rowland, S.J., 1992. Biodegradation studies of unresolved complex mixtures of hydrocarbons model UCM hydrocarbons and the aliphatic UCM. Organic Geochemistry 18, 17-22.
Gough, M.A., Rowland, S.J., 1990. Characterization of unresolved complex mixtures of
TE D
hydrocarbons in petroleum. Nature 344, 648-650. Hu, S.Z., Li, S.F., Cao, J., Zhang, D.M., Ma, J., He, S., Wang, X.L., Wu, M., 2014. A comparison
EP
of normal and reversed phase columns in oil analysis by comprehensive two-dimensional gas
AC C
chromatography with time-of-flight mass spectrometry. Petroleum Science and Technology 32, 565-574.
Huang, H., Jin, G., Lin, C., Zheng, Y., 2003. Origin of an unusual heavy oil from the Baiyinchagan depression, Erlian basin, northern China. Marine and Petroleum Geology 20, 1-12. Kiepper, A.P., Casilli, A., Azevedo, D.A., 2014. Depositional paleoenvironment of Brazilian
17
ACCEPTED MANUSCRIPT
crude oils from unusual biomarkers revealed using comprehensive two dimensional gas chromatography coupled to time of flight mass spectrometry. Organic Geochemistry 70,
RI PT
62-75. Killops, S.D., Al-Juboori, M.A.H.A., 1990. Characterisation of the unresolved complex mixture (UCM) in the gas chromatograms of biodegraded petroleums. Organic Geochemistry 15,
SC
147-160.
M AN U
Korkmaz, S., Kara-Gülbay, R., İztan, Y.H., 2013. Organic geochemistry of the Lower Cretaceous black shales and oil seep in the Sinop Basin, Northern Turkey: An oil–source rock correlation study. Marine and Petroleum Geology 43, 272-283.
Larter, S., Huang, H., Adams, J., Bennett, B., Snowdon, L.R., 2012. A practical biodegradation
66-76.
TE D
scale for use in reservoir geochemical studies of biodegraded oils. Organic Geochemistry 45,
EP
Li, M., Zhang, S., Jiang, C., Zhu, G., Fowler, M., Achal, S., Milovic, M., Robinson, R., Larter, S.,
AC C
2008. Two-dimensional gas chromatograms as fingerprints of sour gas-associated oils. Organic Geochemistry 39, 1144-1149. Li, N., Huang, H., Jiang, W., Wu, T., Sun, J., 2015a. Biodegradation of 25-norhopanes in a Liaohe Basin (NE China) oil reservoir. Organic Geochemistry 78, 33-43. Li, S., Cao, J., Hu, S., 2015b. Analyzing hydrocarbon fractions in crude oils by two-dimensional gas chromatography/time-of-flight mass spectrometry under reversed-phase column system.
18
ACCEPTED MANUSCRIPT
Fuel 158, 191-199. Li, S., Hu, S., Cao, J., Wu, M., Zhang, D., 2012. Diamondoid characterization in condensate by
RI PT
comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry: the Junggar Basin of northwest China. International Journal of Molecular Sciences 13,
SC
11399-11410.
Liu, Z.Y., Phillips, J.B., 1991. Comprehensive 2-dimensional gas-chromatography using an
M AN U
on-column thermal modulator interface. Journal of Chromatographic Science 29, 227-231. Luo, G., Hallmann, C., Xie, S., Ruan, X., Summons, R.E., 2015. Comparative microbial diversity and redox environments of black shale and stromatolite facies in the Mesoproterozoic
TE D
Xiamaling Formation. Geochimica et Cosmochimica Acta 151, 150-167. Mao, D., Weghe, H.V.D., Lookman, R., Vanermen, G., Brucker, N.D., Diels, L., 2009. Resolving the unresolved complex mixture in motor oils using high-performance liquid chromatography
EP
followed by comprehensive two-dimensional gas chromatography. Fuel 88, 312-318.
AC C
Oliveira, C.R., Ferreira, A.A., Oliveira, C.J.F., Azevedo, D.A., Santos Neto, E.V., Aquino Neto, F.R., 2012a. Biomarkers in crude oil revealed by comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry: Depositional paleoenvironment proxies. Organic Geochemistry 46, 154-164. Oliveira, C.R., Oliveira, C.J.F., Ferreira, A.A., Azevedo, D.A., Aquino Neto, F.R., 2012b. Characterization of aromatic steroids and hopanoids in marine and lacustrine crude oils using
19
ACCEPTED MANUSCRIPT
comprehensive two dimensional gas chromatography coupled to time-of-flight mass spectrometry (GCxGC-TOFMS). Organic Geochemistry 53, 131-136.
RI PT
Pawlowska, M.M., Butterfield, N.J., Brocks, J.J., 2013. Lipid taphonomy in the Proterozoic and the effect of microbial mats on biomarker preservation. Geology 41, 103-106.
SC
Peacock, E.E., Hampson, G.R., Nelson, R.K., Xu, L., Frysinger, G.S., Gaines, R.B., Farrington, J.W., Tripp, B.W., Reddy, C.M., 2007. The 1974 spill of the Bouchard 65 oil barge: petroleum
M AN U
hydrocarbons persist in Winsor Cove salt marsh sediments. Marine Pollution Bulletin 54, 214-225.
Peters, K.E., Walters, C.C., Moldowan, J.M., 2005a. Biomarkers and isotopes in the environment and human history, Biomarker Guide, Second ed. Cambridge University Press, New York, pp.
TE D
1-474.
Peters, K.E., Walters, C.C., Moldowan, J.M., 2005b. Biomarkers and isotopes in petroleum
EP
systems and earth history, Biomarker Guide, Second ed. Cambridge University Press, New
AC C
York, pp. 475-1132.
Phillips, J.B., Beens, J., 1999. Comprehensive two-dimensional gas chromatography: a hyphenated method with strong coupling between the two dimensions. Journal of Chromatography A 856, 331-347. Robson, J.N., Rowland, S.J., 1988. Biodegradation of highly branched isoprenoid hydrocarbons: A possible explanation of sedimentary abundance. Organic Geochemistry 13, 691-695.
20
ACCEPTED MANUSCRIPT
Rubinstein, I., Strausz, O.P., Spyckerelle, C., Crawford, R.J., Westlake, D.W.S., 1977. The origin of the oil sand bitumens of Alberta a chemical and microbiological simulation study.
RI PT
Geochimica et Cosmochimica Acta 41, 1341-1353. Scarlett, A., Galloway, T.S., Rowland, S.J., 2007. Chronic toxicity of unresolved complex mixtures (UCM) of hydrocarbons in marine sediments. Journal of Soils and Sediments 7,
SC
200-206.
M AN U
Silva, R.S.F., Aguiar, H.G.M., Rangel, M.D., Azevedo, D.A., Aquino Neto, F.R., 2011. Comprehensive two-dimensional gas chromatography with time of flight mass spectrometry applied to biomarker analysis of oils from Colombia. Fuel 90, 2694-2699. Simoneit, B.R.T., Lein, A.Y., Peresypkin, V.I., Osipov, G.A., 2004. Composition and origin of
TE D
hydrothermal petroleum and associated lipids in the sulfide deposits of the Rainbow field (Mid-Atlantic Ridge at 36°N). Geochimica et Cosmochimica Acta 68, 2275-2294.
EP
Soares, R.F., Pereira, R., Silva, R.S.F., Mogollon, L., Azevedo, D.A., 2013. Comprehensive
AC C
two-dimensional gas chromatography coupled to time of flight mass spectrometry: new biomarker parameter proposition for the characterization of biodegraded oil. Journal of the Brazilian Chemical Society 24, 1570-1581. Tran, T.C., Logan, G.A., Grosjean, E., Harynuk, J., Ryan, D., Marriott, P., 2006. Comparison of column phase configurations for comprehensive two dimensional gas chromatographic analysis of crude oil and bitumen. Organic Geochemistry 37, 1190-1194.
21
ACCEPTED MANUSCRIPT
Tran, T.C., Logan, G.A., Grosjean, E., Ryan, D., Marriott, P.J., 2010. Use of comprehensive two-dimensional
gas
chromatography
time-of-flight
mass
spectrometry
for
the
Geochimica et Cosmochimica Acta 74, 6468-6484.
RI PT
characterization of biodegradation and unresolved complex mixtures in petroleum.
Ventura, G.T., Hall, G.J., Nelson, R.K., Frysinger, G.S., Raghuraman, B., Pomerantz, A.E.,
SC
Mullins, O.C., Reddy, C.M., 2011. Analysis of petroleum compositional similarity using
M AN U
multiway principal components analysis (MPCA) with comprehensive two-dimensional gas chromatographic data. Journal of Chromatography A 1218, 2584-2592. Ventura, G.T., Kenig, F., Reddy, C.M., Frysinger, G.S., Nelson, R.K., Mooy, B.V., Gaines, R.B., 2008. Analysis of unresolved complex mixtures of hydrocarbons extracted from Late Archean
TE D
sediments by comprehensive two-dimensional gas chromatography (GC×GC). Organic Geochemistry 39, 846-867.
EP
Ventura, G.T., Simoneit, B.R.T., Nelson, R.K., Reddy, C.M., 2012. The composition, origin and fate of complex mixtures in the maltene fractions of hydrothermal petroleum assessed by
AC C
comprehensive two-dimensional gas chromatography. Organic Geochemistry 45, 48-65. von Mühlen, C., Zini, C.A., Caramão, E.B., Marriott, P.J., 2006. Applications of comprehensive two-dimensional gas chromatography to the characterization of petrochemical and related samples. Journal of Chromatography A 1105, 39-50. Wang, G., Cheng, B., Wang, T.G., Simoneit, B.R.T., Shi, S., Wang, P., 2014. Monoterpanes as
22
ACCEPTED MANUSCRIPT
molecular indicators to diagnose depositional environments for source rocks of crude oils and condensates. Organic Geochemistry 72, 59-68.
RI PT
Wang, P., 1993. The mass spectrum criterion of petroleum biomarkers. Petroleum Industry Press, Beijing.
SC
Wang, T.G., Simoneit, B.R.T., 1995. Tricyclic terpanes in Precambrian bituminous sandstone from the eastern Yanshan region, North China. Chemical Geology 120, 155-170.
M AN U
Wu, L., Liao, Y., Fang, Y., Geng, A., 2012. The study on the source of the oil seeps and bitumens in the Tianjingshan structure of the northern Longmen Mountain structure of Sichuan Basin, China. Marine and Petroleum Geology 37, 147-161.
TE D
Xiang, B., Zhou, N., Ma, W., Wu, M., Cao, J., 2015. Multiple-stage migration and accumulation of Permian lacustrine mixed oils in the central Junggar Basin (NW China). Marine and Petroleum Geology 59, 187-201.
EP
Xie, L., Sun, Y., Yang, Z., Chen, J., Jiang, A., Zhang, Y., Deng, C., 2013. Evaluation of
AC C
hydrocarbon generation of the Xiamaling Formation shale in Zhangjiakou and its significance to the petroleum geology in North China. Science China Earth Sciences 56, 444-452. Zhang, Z., Hu, W., Song, X., Zhang, C., Zhang, Q., Jin, J., 2014. A comparison of results from two different flash pyrolysis methods on a solid bitumen sample. Organic Geochemistry 69, 36-41. Zhu, G., Wang, H., Weng, N., Huang, H., Liang, H., Ma, S., 2013. Use of comprehensive 23
ACCEPTED MANUSCRIPT
two-dimensional gas chromatography for the characterization of ultra-deep condensate from
AC C
EP
TE D
M AN U
SC
RI PT
the Bohai Bay Basin, China. Organic Geochemistry 63, 8-17.
24
ACCEPTED MANUSCRIPT
Table and Figure Captions
from the Mesoproterozoic Xiamaling shale by GC × GC – TOFMS.
RI PT
Table 1. Retention time for C12 – C14 paraffin hydrocarbons, mono- and bicyclic alkanes detected
SC
Figure 1. TIC chromatogram of the extracted saturated fraction of the Mesoproterozoic
M AN U
Xiamaling shale analyzed by GC – MS.
Figure 2. GC × GC – TOFMS TIC chromatogram of UCM analyzed by the normal-phase column system.
column system.
TE D
Figure 3. GC × GC – TOFMS TIC chromatogram of UCM analyzed by the reversed-phase
EP
Figure 4. Characteristics of UCM with different fragment ions analyzed by the GC × GC – TOFMS reversed-phase system (m/z 185 to 198). Abbreviations, Par: Paraffins; MAk:
AC C
Monocyclic Alkanes; BAk: Bicyclic Alkanes; TAk: Tricyclic Alkanes; MAr: Monocyclic Aromatics; CAr: Cycloalkyl Aromatics; BAr: Bicyclic Aromatics.
Figure 5. Characterization of UCM by the GC × GC – TOFMS reversed-phase column system. (A) m/z 191 mass chromatogram. (B) Structures of individual compounds in UCM corresponding to circles a, b and c in Figure A.
25
ACCEPTED MANUSCRIPT
Figure 6. GC × GC – TOFMS summed mass chromatograms showing the paraffins, mono-cyclic and bicyclic alkanes of UCM. (A) Fragment ion m/z 113+84×3+137×5 by normal-phase column system. (B) Fragment ion m/z 113+84×3+137×5 by reversed-phase column system. Their mass
RI PT
spectra of individual compounds a, b, c, d, e, f, g, and h in Figures A and B are shown in Figures 7 and 8, respectively, and their names were identified and listed in Table 1.
SC
Figure 7. Mass spectra of compounds a, b, c, d, e, f, g and h in Figure 6A.
AC C
EP
TE D
M AN U
Figure 8. Mass spectra of compounds a, b, c, d, e, f, g and h in Figure 6B.
26
ACCEPTED MANUSCRIPT
Table 1. Retention time for C12 – C14 paraffin hydrocarbons, mono-cyclic alkanes and bicyclic alkanes in the analysis of the Mesoproterozoic Xiamaling shale sample by GC × GC – TOFMS.
Normal-phase
Molecular Compound name
a
1082
2-Ethyldecahydro-Naphthalene
C12H22
166
1622, 1.780
b
1116
Hexylcyclohexane
C12H24
168
1646, 1.690
c
1145
1-Ethyldecahydro-Naphthalene
C12H22
166
1658, 1.830
d
1170
Tridecane
C13H28
184
1676, 1.520
1.830-1.520=0.31 s
e&f
1777
C13H24
180
1982, 1.840
Difference in the first-dimensional retention time between compounds f and h:
C13H26
182
2024, 1.750
2036-1982=54 s
weight
M AN U
2-Propyldecahydro-Naphthalene 1-Propyldecahydro-Naphthalene g
h
1887
Tetradecane
C14H30
Maximum difference in the first-dimensional retention time among the four compounds: 1676-1622=54 s
Maximum difference in the second-dimensional retention time among the four compounds:
198
2036, 1.570
Difference in the second-dimensional retention time between compounds f and h: 1.840-1.570=0.27 s
C12H24
168
741, 3.110
Tridecane
C13H28
184
783, 4.020
1029
2-Ethyldecahydro-Naphthalene
C12H22
166
804, 2.900
Maximum difference in the second-dimensional retention time among the four compounds:
c
1112
1-Ethyldecahydro-Naphthalene
C12H22
166
846, 2.940
4.020-2.900=1.12 s
g
1564
Heptylcycohexane
C13H26
182
1021, 3.810
e
1675
2-Propyldecahydro-Naphthalene
C13H24
180
1063, 3.520
h
1706
Tetradecane
C14H30
198
1077, 4.780
Difference in the second-dimensional retention time between compounds f and h:
f
1735
1-Propyldecahydro-Naphthalene
C13H24
180
1091, 3.460
4.780-3.460=1.32 s
889
d
997
a
Hexylcyclohexane
TE D
b
column
AC C
system
Heptylcycohexane
EP
Reversed-phase
1859
Difference in retention time
RI PT
Formula
column system
1st D & 2nd D time (s)
Peak No.
Label
SC
Type
Maximum difference in the first-dimensional retention time among the four compounds: 846-741=105 s
Difference in the first-dimensional retention time between compounds f and h: 1091-1077=14 s
27
ACCEPTED MANUSCRIPT
Figure 1 nC14
nC15
abundance
nC16 nC12
nC23 nC17 nC18nC19
nC25 nC27
TIC
nC21
RI PT
nC13
nC11
UCM
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
EP
TE D
M AN U
Time (min)
AC C
10.00
SC
nC10
28
ACCEPTED MANUSCRIPT
Bicyclic Aromatics
Cycloalkyl Aromatics
RI PT
Figure 2
Monocyclic Aromatics UCM
Tricyclic Alkanes
Bicyclic Alkanes Monocyclic Alkanes Paraffins
AC C
EP
TE D
M AN U
SC
Naphthalene
29
ACCEPTED MANUSCRIPT
RI PT
Figure 3
Paraffins
nC21
UCM
C20, m/z 82, WM=280
SC
Monocyclic Alkanes
Bicyclic Alkanes
C19
Tricyclic Alkanes
C 19
117 63 60
77
91 102
80
100
146
128 120
140
128 63
87 80
102 100
120
Bicyclic Aromatics
AC C
EP
TE D
60
74
M AN U
Monocyclic Aromatics
Cycloalkyl Aromatics
30
ACCEPTED MANUSCRIPT
Figure 4
Par
Par
MAk BAk TAk MAr CAr BAr
MAk BAk TAk MAr CAr BAr
Par MAk BAk TAk MAr CAr BAr
Par
TE D
MAk BAk TAk MAr CAr BAr
Par
MAk BAk TAk MAr CAr BAr
Par
Par
MAk BAk TAk MAr CAr BAr
MAk BAk TAk MAr CAr BAr
M AN U
Par MAk BAk TAk MAr CAr BAr
SC
Par MAk BAk TAk MAr CAr BAr
RI PT
Par MAk BAk TAk MAr CAr BAr
Par
Par
MAk BAk TAk MAr CAr BAr
MAk BAk TAk MAr CAr BAr
Par
Par
MAk BAk TAk MAr CAr BAr
MAk BAk TAk MAr CAr BAr
AC C
EP
Par
MAk BAk TAk MAr CAr BAr
31
ACCEPTED MANUSCRIPT
Figure 5 79
67
109 135
100
150
100
200
150
149
247
191 200
100
250
150
191
247
177 200
290
211 240 100
250
150
200
C21 TT
C20 TT
A
81
123
95
149
220
150
81
123
95
191
300
191
95
68
250
123
RI PT
95
67
82
C19 TT
163
276
243
100
C18 TT
150
200
250
67
95
67
a
95
123
123 163
67 135 121 149
b 91 105
100
150
133
161
100
150
c
200
60
77 80
129
169
1000
155
190
91 105 65 77
100 120 140 160 180 200
a
60
80
143
190
100 120 140 160 180 200
b
82 97
130
183
100
150
150
200
262
250
226 213
200
63
89
115
100
195 179
252 223
143 150
200
250
c
AC C
EP
TE D
B
100
191 177 206
149
250
M AN U
65
200
206
119 147
191
SC
81
233 248
32
ACCEPTED MANUSCRIPT
Figure 6
RI PT
A Aromatic Hydrocarbon
b
138
d C13H28
C12H26
B
e f g h
C14H30
222
SC
c
a
208
C16H34
M AN U
152
194
180
166
C15H32
C17H36
C17H36
C18H38
C18H38
C16H34
TE D
C15H32
C14H30
h
C13H28
d
208
194
b
ef
EP
C12H26
g
222
ac
Aromatic Hydrocarbon
AC C
166
180
152
138
33
ACCEPTED MANUSCRIPT
Figure 7 Peak True - sample "20110109-alk1-Sat-2D:1", peak 1082 Peak True - sample "20110109-alk1-Sat-2D:1", peak 1777 , at 1622 , 1.780 sec , sec , at 1982 , 1.840 sec , sec
a
67
e&f
81
1000
95
67
137
95
166
109
RI PT
81
1000
137
180
60 80 100 120 140 160 60 80 100 120 140 160 180 Peak True - sample "20110109-alk1-Sat-2D:1", peak 1116 Peak True - sample "20110109-alk1-Sat-2D:1", peak 1777 , at 1646 , 1.690 sec , sec , at 1982 , 1.840 sec , sec
b 67 168
67
e&f
81
1000
83
SC
1000
95
137
180
M AN U
60 80 100 120 140 160 60 80 100 120 140 160 180 Peak True - sample "20110109-alk1-Sat-2D:1", peak 1145 Peak True - sample "20110109-alk1-Sat-2D:1", peak 1859 , at 1658 , 1.830 sec , sec , at 2024 , 1.750 sec , sec
c
81
1000
67
g
1000
95
83
137
67
166
109 123
182
98
60 80 100 120 140 160 60 80 100 120 140 160 180 Peak True - sample "20110109-alk1-Sat-2D:1", peak 1170 Peak True - sample "20110109-alk1-Sat-2D:1", peak 1887 , at 1676 , 1.520 sec , sec , at 2036 , 1.570 sec , sec 1000 71 85 98 112 80
100
120
h
1000 71 85 98 112
184
140
160
180
60
80
154
198
100 120 140 160 180 200
AC C
EP
60
TE D
d
34
ACCEPTED MANUSCRIPT
Figure 8
RI PT
Peak True - sample "20110104-alk1-2D:1", peak 889, at 7 Peak True - sample "20110104-alk1-2D:1", peak 1564, at 41 , 3.110 sec , sec 1021 , 3.810 sec , sec
g
b 1000
1000
83
83
67
69
168
98
97
125
154
182
d
1000
1000
81
137
M AN U
67
154
e
95
71 83 98 113
SC
60 80 100 120 140 160 60 80 100 120 140 160 180 Peak True - sample "20110104-alk1-2D:1", peak 997, at 7 Peak True - sample "20110104-alk1-2D:1", peak 1675, at 83 , 4.020 sec , sec 1063 , 3.520 sec , sec
184
180
123
60 80 100 120 140 160 180 60 80 100 120 140 160 180 Peak True - sample "20110104-alk1-2D:1", peak 1029, at Peak True - sample "20110104-alk1-2D:1", peak 1706, at 804 , 2.900 sec , sec 1077 , 4.780 sec , sec 81
1000
h
a
95
1000
67 137 110 123
71
166 151
85
99
126
198
155
TE D
60 80 100 120 140 160 60 80 100 120 140 160 180 200 Peak True - sample "20110104-alk1-2D:1", peak 1112, at Peak True - sample "20110104-alk1-2D:1", peak 1735, at 1091 , 3.460 sec , sec 846 , 2.940 sec , sec
c
81
1000
95
67
137
EP
80
100
120
140
160
137 180
107 60
80
100
120
140
160
180
AC C
60
95
67
166
109 123
f
81
1000
35
ACCEPTED MANUSCRIPT Highlights: UCM present in the Mesoproterozoic Xiamaling shale, North China. Detailed C10–C25 compounds were identified in UCM by GC × GC - TOFMS.
RI PT
Results by reversed-phase column system are better than normal-phase column system.
AC C
EP
TE D
M AN U
SC
UCM was formed by isomerization of organic molecules besides microbial activities.