25th International Meeting on Organic Geochemistry IMOG 2011

P-019
Influence of extraction temperature on the chemical composition
of soil lipids
Csanád Sajgó 1 , József Fekete 1 , Tünde Nyilas 2 , Magdolna Hetényi 2
1 Institute for Geochemical Research, Hungarian Academy of Sciences, Budapest, Hungary, 2 University of
Szeged, Szeged, Hungary (corresponding author:sajgo@geochem.hu)
The composition of soil lipids was compared in five
samples at three sites having different soil characters
from Hungary. The aim of this work is to study the
lipid fractions of the organic matter occurring in
different soil environment and the effect of extraction
temperature on lipid composition. Chernozem (A, AB
and B horizons), red clayey rendzina (A horizon),
typical meadow soil (A horizon) soils were chosen for
this study. For the extraction of lipids from soils
traditional solvents were used: i) n-hexane (Ha) ii)
chloroform/methanol (3/1, v/v; CMa), both shaken
rigorously (3*20 hours) at room temperature and iii)
chloroform (Cb), iiii) benzene/acetone/methanol
(70/15/15, v/v; BAMb), both extracted for 40 hours at
elevated temperature in Soxhlet apparatus (a:
ambient, b: boiling). The carbon-normalized averaged
lipid content varied: 0.22, 0.69, 0.34 and 1.48 mg/g in
different extracts, respectively. The proportion of
aliphatic hydrocarbons relative to aromatic ones and
the proportion of �CH to �NSO (resins) show
characteristic variation (0.9, 1.12, 0.75 and 0.34, 0.25,
0.11) in CMa, Cb, BAMb lipids, respectively.
GC examinations of the non-aromatic hydrocarbon
fractions from lipids at ambient temperature extraction
revealed mainly even-numbered n-alk-1-enes ranging
from n-C14:1 to n-C28:1, maximizing at n-C18:1, n-C20:1
and n-C22:1, n-C24:1, n-C26:1, with moderate
contribution of n-alkanes (n-C14–n-C26). Similar
distributions are rare [1, 2]. The ―boiling extracts‖
show reverse picture. Five n-alkane and alk-1-ene
ratios demonstrate the very considerable difference
between compositions of extraction yields of soils
gained at room temperature and boiling temperature
of solvents [(o+n)C22-/(o+n)C23+, �o/�n, �odd/�even,
Paq, �o+�n (Paq = (nC23 + nC25)/(nC23 + nC25 + nC29 +
nC31); o = n-alk-1-enes, n= n-alkanes)] in Fig 1.
Similar differences are also reflected in the stable
isotopic composition. The small (~0.5‰), but regular
variance of δ13C, and the large (~20‰) variance of
δD in the resin fractions show that the compositions of
the OM obtained with different solvents and
temperatures are different, as well as the proportions
of the exchangeable H.
Our observation of temperature effect on composition
of lipids is scientific novelty.
Fig. 1 n-alkane and alk-1-ene ratios in hexane
a(mbient) and benzene/acetone/methanol b(oiling)
extracts
This work was funded by the Hungarian Scientific
Research Fund (OTKA) through grant K81181.
References
[1] Hetényi, M., Nyilas, T., Sajgó, Cs. 2010. Organic
geochemical evidence of late Pleistocene–Holocene
environmental changes in the Lake Balaton region
(Hungary). Organic Geochemistry, 41, 915-923
[2] Ekpo, B. O., Oyo-Ita, O. E., Wehner, H., 2005.
Even-n-alkane/alkene predominances in surface
sediments from the Calabar River, SE Niger Delta,
Nigeria. Naturwissenschaften 92, 341–346.
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