Advances in Chemical Engineering and Science, 2011, 1, 163-168
doi:10.4236/aces.2011.13024 Published Online July 2011 (http://www.SciRP.org/journal/aces)
Determination of Sterane an d Tri terpane in the
Tamsagbulag Oilfield
Erdenee Enkhtset seg1, Batdelger Byambagar1, Dalantai Monkhoobor2,
Budeebazar Avid3*, Avirmed Tuvshinjargal4
1Mongolian University of Science and Technololgy, Ulaanbaatar, Mongolia
2National University of Mongolia , Ulaanbaatar, Mongolia
3Mongoli an Academy of Sciences, Ulaanbaatar, Mongolia
4Petroleum authority of Mongolia, Ulaanbaatar, Mongolia
Received March 9, 2011; revised April 15, 2011; accepted April 26, 2011
Abstract
Crude oils representing four different holes from the Tamsagbulag oilfield were analyzed by gas chromato-
graphy-mass spectrometry (GC/M S ) spectroscopy. 52 biomarker compounds, 34 pentacyclic triterpanes and
18 steranes were identified and semi-quantitatively determined by selective ion monitoring (SIM)
chromatography. Depending on the oil source, the variation in the pentacyclic triterpanes distribution is more
significant than the variation in the sterane distribution. It is said that pregnane and honopregnane originated
during the period of very salty sedimentary accumulation in the condition of diagenesis.
Keywords: Crude Oil, Biomarker, GC-MS, Tamsagbulag Oilfield
1. Introductio n
Biomarkers are complex molecular fossils derived from
once living organisms and it can provide information on
the organic source materials, environmental conditions
during its deposition, the thermal maturity experienced
by a rock or oil, and the degree of biodegradation. Stu-
dies on identification and quantification of biomarker
compounds have obtained great importance for recogni-
tion and classification of crude oil source. Sterane and
hopane biomarkers have great potential in helping to
identify and allocate hydrocarbon sources [1-9].
It is very important to study polyaromatic aliphatic
hydrocarbons with carbon of C27 or higher hydrocarbon
chain like steroid and triterpenoid for the geochemical
investigation of crude oil and other caustobiolithes. The
chemical type and relative content of biomarker com-
pounds in specific oil is considered as its unique finger-
print. Among the various types of biomarkers, triterpanes
and steranes are the best target molecules for identifica-
tion and quantification. These molecules, with a molecu-
lar weight of about 250 - 400, possess a relative high
concentration in crude oil and they are resistant to petr o-
chemical and microbial degradation [4,5]. Therefore,
they have found their use in tracing the oil source, its
characteristics, degree of weathering and the fate of
spilled oil in the environment [6,7]. Utilizing the GC and
GC/MS technique made it possible to arrive at a clear
characterization and classification of crude oils accord-
ing to their sources [8]. Source specific parameters (viz.
DBT/P, Pr/Ph, C29/C27 sterane and hopane/sterane ra-
tios and tri- and tetra-cyclic terpane distributions) indi-
cate that family oils derived from a marine shale depo-
sited under sub-oxic conditions, whereas family oils de-
rived from terrigenous source, contain n-alkanes that are
less depleted in 13C, consistent with their derivation from
a terrigenous source rock and their higher thermal matur-
ity. The more negative n-alkane 13C profiles of the
family oils reflect their marine source [9]. The research
demonstrated that the biomarker distribution and carbon
isotopic composition could be used to differentiate oils
derived from various lacustrine environments [10,11].
Recently several researchers have paid more attention
on biomarker and geochemical investigation of the
Mongolian crude oil. Composition of the hydrocarbons
and structure of the heteroatom compounds with high
molecular weight from the Zuunbayan, Tsagaan els and
19-3, 19-12, 19-13, 19-14, 19-17 wells of Tamsagbulag
oilfields have been studied by Khongorzul. Based on the
results, the author has estimated product properties of

E. ENKHTSETSEG ET AL.
164
crude oil fractions and proposed it’s suitable applicaton
and as well as refinery process [12]. Another investiga-
tion has been done on Toson Uul and Zuunbayan oil
fields, specially it is focused on the effect of depths for
the properties and geochemical study of crude oil and
sedimentary rock [13]. The structure and compositions of
the hydrocarbons from the Tamsagbulag and Zuunbayan
oilfields are studied by Sainbayar [14]. The author has
focused on the compositions of the light fractions, espe-
cially on normal and isoparapynic hydrocarbons and
tried to characterize the geochemical classification.
The aim of this research is to study crude oils from
four new holes from the Tamsagbulag oilfield by using
chromatographic method.
2. Materials and Methods
The crude oil samples representing the 19-14, 19-28,
19-31 and 19-34 wells from the Tamsagbulag oilfield
from Mongolia have been selected for investigation. The
selected samples are separated into 3 different fractions
like paraffin, naphtene and aromatics. GC/MS measure-
ments were performed on a Thermo-Finnigan Trace DSQ
mass spectrometer coupled to a Thermo Finnigan Trace
GC with a split injector (1:20) and a 0.25 µm HP-5MS
fused silica capillary column with a 60 m × 0.35 mm
inner diameter. The temperature was held at 40˚C for 3
min and then increased to 250˚C at 5˚C/min intervals,
with helium flow rate of 3 ml/min. The EI-MS ionization
voltage was 70 eV (electron impact ionization), and the
ion source and interface temperature were both 250˚C.
3. Results and Discussion
The two classes of biomaker, pentacyclic triterpanes and
steranes were identified under the chosen MS condition.
Together with steranes, terpanes, triterpanes belong to
the most important petroleum hydrocarbons that retained
the characteristic structure of the original biological
compounds [2]. Tricyclics, tetracyclics, hopanes, and
other compounds contribute to the sterane and terpane
fingerprint mass chromatogram (m/z = 217 and 191)
commonly used to relate oils and source rocks. GC-MS
chromatograms of the crude oil from Tamsagbulag oil-
field are shown in Figures 1-2, the assignments of the
peaks are summarized in Tables 1-2.
Molecular ratios measured from these mass chroma-
tograms help illustrate similarities in the distributions
of these biomarker compounds.
The crude oil was characterized by measuring the
normalized peak heights of 18 steranes and 34 pentacyc-
lic triterpanes.
The sterane and terpane concentrations of the crude oil
from 19-14, 19-28, 19-31 and 19-34 wells of the Tam-
sagbulag oilfield are shown in Tables 3-4.
Based on the results shown in above, the contents of
the biosteranes, isosteranes and diasteranes and composi-
tion of the hydrocarbons from the hopane homologies
were incorporated in Tables 5 and 6.
The tables show that the composition of petroleum
from some holes of Tamsagbulag oil field contains bios-
teranes and isosteranes with hydrocarbon atoms of C27 -
C29 and the ethylcholestanes with hydrocarbon atoms of
C29 make up much of it. It mean s that major organic sub-
stances of this petroleum originated from oddments of
upper pla nts on the Ea rth (Figure 1, Tables 3 and 5.)
Therefore pregnane (C21) and honopregnane (C22)
which are the parts with small molecules of homologous
alignment of sterane were found in the petroleum of the
above mentioned oil field. It is said that pregnane and
Figure 1. Mass chromatograms of oil samples of 19-31 well of the Tamsagbulag oilfield for steranes (m/z 217).

E. ENKHTSETSEG ET AL.
165
Figure 2. Mass chromatograms of oil samples of 19-31 well of the Tamsagbulag oilfield for terpanes (m/z 191).
Table 1. GC-MS peak identification for Figure 1.
Peak label
Compound
Elemental composition
3
20S-áâá-Diacholestane
С27Н48
4 20R-
áâá
-Diacholestane С27Н48
5
20S-ááá-Cholestane
С
27
Н
48
6
20R-áââ-Cholestane
С27Н48
7
20S-áââ-Cholestane
С27Н48
8
20R-ááá-Cholestane
С27Н48
9 20R-24-Ethyl-10
á
13
â
17
á
-diacholestane С29Н52
10
20S-24-Ethyl-10á13á18â-diacholestane
С
29
Н
52
11
20S-24-Methyl-ááá-cholestane
С28Н50
12
20R-24-Methyl-áââ-cholestane
С28Н50
13
20S-24-Methyl-áââ-cholestane
С28Н50
14 20R-24-Methyl-
ááá
-cholestane С28Н50
15
20S-24-Ethyl-ááá-cholestane
С
29
Н
52
16
20R-24-Ethyl-áââ-cholestane
С29Н52
17
20S-24-Ethyl-áââ-cholestane
С29Н52
18
20R-24-Ethyl-ááá-cholestane
С29Н52
honopregnane originated during the period of very salty
sedimentary accumulation in the condition of diagenesis.
In the petroleum from holes 19-14, 19-28 and 19-31 of
Tamsagbulag, most of diasteranes which are the newly
formed isomer of biosteranes are hydrocarbon com-
pounds of C27 (7.5% - 9.5% relatively). The petroleum of
the hole 19-34 contains relatively little amount of hy-
drocarbon compounds of C27 which is only 1.09%. In
other words, C27 > C29 for diasteranes of petroleum of
holes 19-14, 19-28 and 19-31 while C27 < C29 for hole
19-34. Diasteranes of petroleum are useful for determin-
ing component of sediment lithology comprised funda-
mental source and original substance of petroleum. The
C29 norhopanes and C30 hopanes are the dominating
biomarkers in all the crude oils which is characteristic for
source rocks rich in terrestrial organic matter [15].
These hydrocarbons’ amount in the petroleum of holes
19-14, 19-28 and 19-31 is relatively more than in petro-
leum of hole 19-34 so it means that the origin of the pe-
troleum of these 3 three holes except 19-34 is relevant
with sedimentary rocks which are rich in aluminum sili-
cate. Tr icyclicterpane amounted of 3% - 15% was dis-
covered from among class of hydrocarbons of terpane
and contents of hopane and norhopane in the 4 holes of
the petroleum were 44% - 47.5%, 6% - 8%, resp ectively.
Homohopanes amount in hydrocarbons of terpane in the
petroleum of the aforementioned 4 holes was accounted
for 25% - 35%. There was a constant decrease of homo-
hopanes with C32-C35 and each pair of epimers had plenty
of (22-S)-epimer s ( Tab les 2 and 4). Processing level of

166 E. ENKHTSETSEG ET AL.
Table 2. GC-MS peak identification for Figure 2.
Peak label
Compound
Elemental composition
1 C19, 14â(methyl)-Tricyclicterpane C19H34
2
C20, 13â(H), 14á(H)-Tricyclicterpane
C20H36
3
C21, 13â(H), 14á(H)-Tricyclicterpane
C21H38
4
C22, 13â(H), 14á(H)- Tricyclicterpane
C22H40
5
C23,13â(H), 14á(H)-Tricyclicterpane
C23H42
6 C24,13â(H), 14á(H)-Tricyclicterpane C24H44
7
C
25
, 13â(H), 14á(H)-Tricyclicterpane
C
25
H
46
8
C26, Tricyclicterpane
C26H48
9
C26, Tricyclicterpane
C26H48
10
C24, Tricyclicterpane
C24H44
11 C28, Tricyclicterpane C28H50
12
C
28
, Tricyclicterpane
C
28
H
50
13
C29, Tricyclicterpane
C29H52
14
C29, Tricyclicterpane
C29H52
15
18á, -22, 29, 30-Trisnorhopane(Ts)
C27H46
16 17á, -22, 29, 30-Trisnorhopane(Tm) C27H46
17
17á, 21â-30-Norhopane
C
29
H
50
18
C29Ts
C29H50
19
18á(H)-Hopane
C30H52
20
17â(H), 21á(H)-Normoretane
C29H50
21 C3017á(H), 21â(H)-Hopane C30H52
22
17â(H), 21á(H)-Moretane
C
30
H
52
23
22S-17á(H), 21â(H)-Homohopane
C31H54
24
C3122R-17á(H), 21â(H)-Homohopane
C31H54
25
Gammacerane
C30H52
26 22R-17â(H), 21á(H)-Homomoretane C31H54
27
22S-17á(H), 21â(H)-Dihomohopane
С
32
Н
56
28
22R-17á(H), 21â(H)-Dihomohopane
С32Н56
29
22S-17á(H), 21â(H)-Trihomohopane
С33Н58
30
22R-17á(H), 21â(H)-Trihomohopane
С33Н58
31 22S-17á(H), 21â(H)-Tetrahomohopane С34Н60
32
22R-17á(H), 21â(H)-Tetrahomohopane
С
34
Н
60
33
22S-17á(H), 21â(H)-Pentahomohopane
С35Н62
34
22R-17á(H), 21â(H)-Pentahomohopane
С35Н62
Table 3. Sterane concentration in the crude oil from Tamsagbulag oilfield, wt%.
ID Compound Formula Molecular
weight
Oil wells
14 28 31 34
S1 5á(H), 14â(H)-Pregnane C21H36 288 2.30 2.80 2.45 1.62
S2 C22 Honopregnane C22H38 302 1.57 1.77 1.52 0.93
S3 20S-áâá-Diacholestane С27Н48 372 4.79 5.46 4.56 0.48
S4 20R-áâá-Diacholestane С27Н48 372 3.17 4.12 3.03 0.61
S11 20S-ááá-Cholestane С27Н48 372 5.05 4.48 4.69 6.64
S12 20R-áââ-Cholestane С27Н48 372 6.08 5.97 6.45 5.39
S13 20S-áââ-Cholestane С27Н48 372 6.28 7.07 6.07 5.49
S14 20R-ááá-Cholestane С27Н48 372 6.38 4.73 6.02 9.78
S15 20R-24-Ethyl-10á13â17á-diacholestane С29Н52 400 3.41 2.99 3.25 3.39
S16 20S-24-Ethyl-10á13á18â-diacholestane С29Н52 400 1.62 1.82 1.74 1.07
S17 20S-24-Methyl-ááá-cholestane С28Н50 386 2.88 3.71 3.12 2.56
S18 20R-24-Methyl-áââ-cholestane С28Н50 386 2.44 2.92 2.62 3.67
S19 20S-24-Methyl-áââ-cholestane С28Н50 386 4.83 4.99 4.96 5.96
S20 20R-24-Methyl-ááá-cholestane С28Н50 386 3.74 3.71 3.84 5.58
S21 20S-24-Ethyl-ááá-cholestane С29Н52 400 10.13 8.53 9.83 12.01
S22 20R-24-Ethyl-áââ-cholestane С29Н52 400 13.08 13.24 12.51 11.22
S23 20S-24-Ethyl-áââ-cholestane С29Н52 400 10.26 10.70 11.43 9.08
S24 20R-24-Ethyl-ááá-cholestane С29Н52 400 12.00 11.00 11.91 14.51

E. ENKHTSETSEG ET AL.
167
Table 4. Terpane c o ncentration in the crude oil from Tamsagbulag oilfield, wt%.
ID Compound Formula
Molecular
weight
Oil wells
14
28
31
34
Т1 C19, 14
â
(methyl)-Tricyclicterpane C19H34 262 0.55 0.70 0.57 0.38
Т
2
C20, 13â(H), 14á(H)-Tricyclicterpane
C
20
H
36
276
0.45
0.56
0.44
1.88
Т3
C21, 13â(H), 14á(H)-Tricyclicterpane
C21H38
290
0.49
0.67
0.48
4.53
Т4
C22, 13â(H), 14á(H)-Tricyclicterpane
C22H40
304
0.09
-
0.10
0.42
Т5
C23, 13â(H), 14á(H)-Tricyclicterpane
C23H42
318
0.42
0.50
0.39
1.87
Т6 C24, 13â(H), 14á(H)-Tricyclicterpane C24H44 332 0.20 0.27 0.23 1.03
Т
7
C25, 13â(H), 14á(H)-Tricyclicterpane
C
25
H
46
346
0.10
-
-
0.81
Т9
C26, Tricyclicterpane
C26H48
360
0.15
0.16
0.14
0.53
Т10
C26, Tricyclicterpane
C26H48
360
-
-
-
-
Т8
C24, Tricyclicterpane
C24H44
332
1.19
1.29
1.14
1.52
Т11 C28, Tricyclicterpane C28H50 388 - - - 1.17
Т
12
C28, Tricyclicterpane
C
28
H
50
388
-
-
0.50
Т13
C29, Tricyclicterpane
C29H52
402
-
-
-
0.35
Т14
C29, Tricyclicterpane
C29H52
402
-
-
-
0.28
Т15
18á, -22,29,30-Trisnorhopane(Ts)
C27H46
370
4.97
5.42
4.37
2.57
Т16 17
á
, -22,29,30-Trisnorhopane(Tm) C27H46 370 3.17 2.86 2.97 3.76
Т
19
17á, 21â-30-Norhopane
C
29
H
50
398
11.77
9.97
11.44
13.49
Т20
C29Ts
C29H50
398
5.52
6.00
5.53
2.57
Т21
18á(H)-Hopane
C30H52
412
2.72
3.26
2.50
1.02
Т22
17â(H), 21á(H)-Normoretane
C29H50
398
1.19
1.47
1.08
0.60
Т23 17á(H), 21â(H)-Hopane C30H52 412 27.42 26.41 27.11 26.91
Т
24
17â(H), 21á(H)-Moretane
C
30
H
52
412
3.51
3.48
3.62
3.53
Т25
22S-17á(H), 21â(H)-Homohopane
C31H54
426
7.92
7.55
8.20
6.48
Т26
22R-17á(H), 21â(H)-Homohopane
C31H54
426
6.08
6.01
6.20
5.02
Т27
Gammacerane
C30H52
412
1.63
1.72
1.89
3.28
Т28 22R-17
â
(H), 21
á
(H)-Homomoretane C31H54 426 1.22 1.14 1.63 2.15
Т
29
22S-17á(H), 21â(H)-Dihomohopane
С
32
Н
56
440
5.29
5.34
5.36
5.25
Т30
22R-17á(H), 21â(H)-Dihomohopane
С32Н56
440
3.82
4.13
3.89
2.75
Т31
22S-17á(H), 21â(H)-Trihomohopane
С33Н58
454
3.05
3.18
3.12
2.04
Т32
22R-17á(H), 21â(H)-Trihomohopane
С33Н58
454
2.10
2.45
2.29
1.19
Т33 22S-17
á
(H), 21
â
(H)-Tetrahomohopane С34Н60 468 2.03 2.10 2.02 0.94
Т
34
22R-17á(H), 21â(H)-Tetrahomohopane
С
34
Н
60
468
1.29
1.39
1.34
0.57
Т35
22S-17á(H), 21â(H)-Pentahomohopane
С35Н62
482
0.98
1.11
1.12
0.40
Т36
22R-17á(H), 21â(H)-Pentahomohopane
С35Н62
482
0.70
0.87
0.81
0.21
Table 5. The sterane concentration in the crude oil from some wells of the Tamsagbulag oilfield, wt%.
Compound Oil wells
14 28 31 34
5á(H), 14â(H)-Pregnane 2.30 2.80 2.45 1.62
C22 Honopregnane
1.57
1.77
1.52
0.93
С27
11.43
9.21
10.71
16.42
С28
6.62
7.42
6.96
8.14
С29
22.13
19.53
21.74
26.52
Total biosterane 40.18 36.16 39.41 51.08
С
27
12.36
13.04
12.52
10.88
С28
7.27
7.91
7.58
9.63
С29
23.34
23.94
23.94
20.3
Total isosterane
42.97
44.89
44.04
40.81
Total normal sterane 83.15 81.05 83.45 91.89
С
27
7.96
9.58
7.59
1.09
С28
-
-
-
-
С29
5.03
4.81
4.99
4.46
∑sterane
12.99
14.39
12.58
5.55
the petroleum of these 4 holes was considered as low
because none of diahopanes was found in their compo-
nent. Some gammaceranes (1.5% - 3%) were found in
the petroleum of holes 19-14, 19-28, 19-31 and 19-34 of
Tamsagbulag oil field and this evidence shows characte-
ristic of highly marine depositional conditions in the en-
vironment of ocean, sea and marshy lake.
4. Conclusions
1) The composition of the sterane and terpane hyrdo-
carbon derivatives of the Tamsagbulag crude oil well
No. 14-19, 28, 31 and 34 has been determined by
GC-MS.
2) Based on the contained biosteranes and isosteranes,

168 E. ENKHTSETSEG ET AL.
Table 6. The hydrocarbon compositions of hopane derivatives in the crude oil from some wells of the Tamsagbulag oilfield,
wt%.
Compound
Oil wells
14
28
31
34
Tricyclicterpane
3.64
4.15
3.49
15.27
Norhopane (Tm + Ts)
8.14
8.28
7.34
6.33
Hopane 47.43 45.64 46.58 43.99
Moretane
4.7
4.95
4.7
4.13
Homohopane
33.26
34.13
34.35
24.85
Homomoretane
1.22
1.14
1.63
2.15
Gammacerane
1.63
1.72
1.89
3.28
the petroleum from some holes of Tamsagbulag oil field,
originated from oddments of upper plants. The content of
the gammacerane, pregnane and honopregnane found in
the petroleum of the aforementioned oil field says that
those are originated during the period of very salty sedi-
mentary accumulation in the condition of diagenesis.
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