Publication Date:
2021-06-21
Description:
Compound-specific radiocarbon (14C) dating often requires working with small samples of 〈 100 μg
carbon (μgC). This makes the radiocarbon dates of biomarker compounds very sensitive to biases caused by
extraneous carbon of unknown composition, a procedural blank, which is introduced to the samples during the
steps necessary to prepare a sample for radiocarbon analysis by accelerator mass spectrometry (i.e., isolating single
compounds from a heterogeneous mixture, combustion, gas purification and graphitization). Reporting accurate
radiocarbon dates thus requires a correction for the procedural blank. We present our approach to assess the
fraction modern carbon (F14C) and the mass of the procedural blanks introduced during the preparation
procedures of lipid biomarkers (i.e. n-alkanoic acids) and lignin phenols. We isolated differently sized aliquots
(6–151 μgC) of n-alkanoic acids and lignin phenols obtained from standard materials with known F14C values.
Each compound class was extracted from two standard materials (one fossil, one modern) and purified using the
same procedures as for natural samples of unknown F14C. There is an inverse linear relationship between the
measured F14C values of the processed aliquots and their mass, which suggests constant contamination during
processing of individual samples. We use Bayesian methods to fit linear regression lines between F14C and 1/mass
for the fossil and modern standards. The intersection points of these lines are used to infer F14Cblank and mblank
and their associated uncertainties. We estimate 4.88 ± 0.69 μgC of procedural blank with F14C of 0.714 ± 0.077 for
n-alkanoic acids, and 0.90 ± 0.23 μgC of procedural blank with F14C of 0.813 ± 0.155 for lignin phenols. These
F14Cblank and mblank can be used to correct AMS results of lipid and lignin samples by isotopic mass balance. This
method may serve as a standardized procedure for blank assessment in small-scale radiocarbon analysis.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
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