25th International Meeting on Organic Geochemistry IMOG 2011

P-028
Characterisation of lignin degradation products from dissolved
organic matter: a comparison of different extraction and
analysis techniques
Jonathan Williams 1,2 , Jennifer Dungait 2 , Roland Bol 2 , Geoffrey Abbott 1
1 Newcastle University, Newcastle upon Tyne, United Kingdom, 2 Rothamsted Research North Wyke,
Okehampton, United Kingdom (corresponding author:jonathan.williams@ncl.ac.uk)
Lignin can degrade rapidly in soils. Recent research
has shown that white-rot fungi, such as Pleurotus
ostreatus, can oxidise lignin within a timescale of 7 to
63 days 1,2 and lignin decomposition is monomer
specific 3 . This has highly significant implications for
determining the mechanisms for C sequestration in
soils. Lignin degrades into phenolic compounds which
are water-soluble and, therefore, prone to be
transported through the soil-water continuum.
Guaiacyl and syringyl lignin monomer units have been
detected in fresh, estuarine and marine waters 4 , and
in deep ocean dissolved organic matter (DOM) 5,6
allowing these compounds to be used as geochemical
biomarkers of plant inputs in diverse systems.
After it is degraded at source, the initial forms in which
lignin enters watercourses are not yet known. In order
to characterise and quantify degraded lignin products
entering the soluble phase in soils, it is first necessary
to determine the best approach to extract and analyse
them. Therefore, the aims of this work were to:
(1) determine the best method for the extraction of
lignin-derived compounds from freshwater (draining
from grassland) in terms of recovery and timeefficiency,
i.e. C18 solid phase extraction (SPE) or
freeze-drying.
(2) compare analytical methods, i.e. on-line py-GC-
MS in the presence of TMAH versus on-line py-GC-
MS versus GC-MS of trimethylsilyl (TMS) derivatives.
The results showed that freeze-drying recovered
considerably more DOM than SPE in terms of mass
(Figure 1). However, C18 silica-based SPE recovered
a greater proportion of identifiable lignin- and
carbohydrate-derived compounds than freeze drying
Gas chromatography-mass spectrometric (GC-MS)
analyses of TMS derivatives of samples extracted by
SPE from freshwater identified: benzoic acid, 4-
[(trimethylsilyl)oxy]-,TMS ester; benzoic acid, 3methoxy-4-[(trimethylsilyl)oxy-],
TMS ester; and 3,4bis[(trimethylsilyl)oxy]-,
TMS ester. Abundant
carbohydrate-derived compounds were also
identified: α-D-Ribofuranoside, methyl 2,3,5-tris-O-
(TMS)-; α-1-Mannopyranoside, methyl 6-deoxy-2,3,4tris-O-(TMS)-;
and β-L-Arabinopyranose, 1,2,3,4tetrakis-O-(TMS)-;
and also lipids including C16:0 and
C18:0 fatty acids. C23 to C32 n-alkanes were the most
abundant compounds from the same samples
extracted using freeze-drying.
Figure 1. Yields of DOM recovered by solid phase
extraction (SPE) and freeze-drying (FD) in relation to
TOC from a range of natural freshwaters, showing
standard error bars.
References
[1] Robertson, S., Mason, S., Hack, E., Abbott, G.D.
(2008) Org. Geochem. 39: 945-951; [2] Vane, C. H.,
Martin, S. C., Snape, C. E., Abbott, G. D. (2001). J.
Agric. Food Chem. 49: 2709-2716; [3] Dungait, J.A.J.,
Stear, N.A., van Dongen, B. E., Bol, R., Evershed,
R.P., (2008). Rapid Commun. Mass Sp. 22: 1631-
1639; [4] Louchouarn, P., S. Opsahl, et al. (2000).
Anal. Chem. 72(13): 2780-2787; [5] Opsahl, S. and R.
Benner (1997). Nature 386(6624): 480-482; [6]
Opsahl, S. and R. Benner (1999). Limnol. and
Oceanogr. 44(8): 2017-2023.
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