25th International Meeting on Organic Geochemistry IMOG 2011

P-058
Characterization of aromatic steroids in marine and lacustrine
crude oils by Comprehensive two-dimensional gas
chromatography time-of-flight mass spectrometry (GCxGC-
TOFMS)
Cristiane Rossi Oliveira 1 , Hélen Gomes Maria Aquiar 2 , Débora Almeida Azevedo 1 ,
Eugênio Santos Neto 2 , Francisco Aquino Neto 1
1 Universidade Federal do Rio de Janeiro, Rio de Janeiro/RJ, Brazil, 2 Petrobras-CENPES, Rio de Janeiro/RJ,
Brazil (corresponding author:rossi.cristiane@yahoo.com.br)
Aromatic steroids from sedimentary organic matter
provide valuable information to assess organic matter
input [1], thermal maturity [2] and correlation of crude
oils [3]. The identification of these compounds is
typically achieved by a series of chemical and
chromatographic separations. The GCxGC technique
proved to be a powerful tool in solving co-elution
problems, commonly observed in GC oil analysis
[4,5]. The aim of this work is to favor the identification
and quantification of aromatic steroids as well as to
improve their application in geochemical studies, due
to difficulties in identifying this class of compounds.
Six Brazilian crude oil samples (three marine and
three lacustrine) were fractionated by liquid
chromatography with silica gel and the aromatic
hydrocarbons were analyzed by GCxGC-TOFMS.
GCxGC separations were performed using a quad-jet
dual-stage N2 modulator and non-polar to polar
column set. The GCxGC-TOFMS system used was a
Pegasus 4D (Leco, St. Joseph, MI, USA).
Analyzing the extracted ion chromatogram (m/z
231+253) of the oil samples (Figure1); it is possible to
see that the amount of monoaromatic steroids with
27, 28 and 29 and triaromatic steroids with 26, 27 and
28 carbon atoms decreases in lacustrine samples
when compared to marine samples.
It is known that with the increase in the degree of
thermal maturity the conversion of long-chain
aromatic steroids homologues (structures 2 and 4)
into short-chain homologues (structures 1 and 3)
increases as the lateral side chains are broken. The
short-chain triaromatic steroid/(short-chain triaromatic
steroid + long-chain triaromatic steroid) ratio values
vary from 0.06 to 0.21 for marine samples and from
0.31 to 0.77 for lacustrine samples, suggesting that
the lacustrine samples have a higher level of thermal
maturity than the marine samples. However, maturity
parameters based on 20S/(20S+20R) and
αββ/(αββ+ααα) sterane (St), TeT24/H30 and Tr/H
ratios showed values varying from 0.13 to 0.45, 0.44
to 0.51, 0.06 to 0.12 and 0.15 to 0.30, respectively,
and are typical values for mid-oil window thermal
maturity. The differences in the distribution of longchain
and short-chain aromatic steroids may reflect
the different origin of these oils and this aspect is
being further evaluated.
References
[1] Requejo, A.G., Sassen, R.; McDonald, T., Denoux, G., Kennicutt,
M.C., Brooks, J.M. (1996) Org. Geochem. 24, 1017-1033.
[2] Zhanjun, Z., Yongjian, J., Zhe, C. (2009) Pet. Explor. Dev. 36, 790-
796.
[3] Hostettler, F.D., Rosenbauer, R.J., Kvenvolden, K.A. (1999) Org.
Geochem. 30, 873-879.
[4] Aguiar, A., Silva Junior, A.I., Azevedo D.A., Aquino Neto F. R.
(2010) Fuel 89, 2760-2768.
[5] Aguiar, A., Aguiar, H., Azevedo, D.A., Aquino Neto, F.R. (2011)
Energy & Fuels, in press
Fig.1. Aromatic biomarker series (m/z 231+253) extracted ion chromatogram obtained by GCxGC-TOFMS from
representative marine and lacustrine crude oil samples.
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