25th International Meeting on Organic Geochemistry IMOG 2011

O-47
Current developments and challenges in compound-specific
radiocarbon analysis
Rienk Smittenberg 1,2,3 , Merle Gierga 1 , Axel Birkholz 1 , Irka Hajdas 4 , Lukas Wacker 4 ,
Michael Schmidt 2 , Stefano Bernasconi 1,2
1 ETH Zurich, Geology, Zurich, Switzerland, 2 University of Zurich, Geography, Zurich, Switzerland,
3 Stockholm University, Geology, Stockholm, Sweden, 4 ETH Zurich, Ion Beam Physics, Zurich, Switzerland
(corresponding author: rienk.smittenberg@geo.su.se)
Besides its use as a dating tool for carbonaceous
materials, radiocarbon ( 14 C) analysis is also a
powerful tool for studies pertaining the carbon cycle,
from the global [1] to the local [2] scale, as well as
other biogeochemical processes. The 5730 yr half-life
of naturally-produced 14 C can provide insights into the
operation of the C cycle over longer time scales, while
C derived from fossil fuel burning ( 14 C-dead), as well
as the 14 C-spike introduced by atmospheric bomb
tests of the mid-20th century, are useful tracers for
the examination of C-cycling over shorter time scales.
Within this framework it is of great interest to look at
different fractions of the carbon pool, down to the
molecular scale, in order to also gain source-specific
insights.
The general introduction of Accelerator Mass
Spectrometry (AMS) in the early 1990s made it
possible to decrease sample size, which triggered the
introduction of compound-specific 14 C analysis in the
1990s [3]. Until recently, 50 microgram C was
regarded as a small sample, but recent improvements
in the design of AMS systems, ion sources and
sample introduction into the AMS, e.g. directly as CO2
gas instead of the traditional graphite, have lowered
the measurable amount of C to less than 5
micrograms [4-6].
Quality control and standard normalization is
traditionally performed by measuring reference
materials (' 14 C-dead' coal and ' 14 C modern' oxalic
acid) after combustion and graphitization. This basic
normalization will always need to be performed.
However, for very small samples significant offsets
from real values can be observed. These are summed
effects of sample preparation: 1) Insufficient
purification/isolation from the matrix, for instance in
the case of individual compounds. 2) Contaminations
added during the purification procedure, sample
handling, and combustion to CO2. 3) Transfer of CO2
to the ion source and subsequent continuous flow
ionization. The accuracy of small-sample radiocarbon
values can only be evaluated with a rigorous
assessment of the parts of this summed factor (see
also e.g. [7]), which may be different for different
types of sample. Hence there is a need for 14 C
standards that are the same as, or as similar as
possible to, the analytes of interest (e.g. a specific
lipid compound, protein, or batch of aerosols) in order
to evaluate and validate the preparation procedures.
We will present a general overview of small-scale
radiocarbon analysis as it is at present conducted at
the ETH Zürich. More specifically, we present a
comparison study between the purification of longchain
fatty acids by the traditionally used preparative
gas chromatography, with a method based on liquid
chromatography, as well as results from lake
sediment samples. Secondly we present a procedure
to isolate branched glycerol dialkyl glycerol
tetraethers, and 14 C results. Finally we present a new
HPLC-based method for the purification of benzene
carboxylic acids (BPCAs), which are molecular
markers for fire-derived black carbon, obtained by
nitric acid digestion of sediments, soils or other
matrices [8]. All these compounds are, once purified,
analyzed on the MIni CArbon Dating System
(MICADAS) equipped with a gas source [5,6].
Extensive testing of this system using a number of
standards indicates that routine compound-specific
radiocarbon analysis is possible on the 10 �g C level.
References:
[1] Galy, V., 2008. Science 322, 943; [2] Trumbore
S., 2009. Annu.Rev.Earth Pl.Sc. 37; [3] Eglinton, T.
I., 1996. Anal. Chem. 68, 904; [4] Bronk Ramsey, C.
1997, Nucl. Instr. Meth. Phys. Res. B 123, 539; [5]
Ruff, M., 2007. Radiocarbon 49, 307; [6] Ruff, M.,
2010. Nucl. Instr. Meth. Phys. Res. B268, 790; [7]
Shah, S. R., 2007. Radiocarbon 49, 82; [8] Schneider,
M.P.W., 2011, Org. Geochem.,42, 275.
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