Publication Date:
2022-05-25
Description:
Author Posting. © Arizona Board of Regents on behalf of the University of Arizona, 2010. This article is posted here by permission of Dept. of Geosciences, University of Arizona for personal use, not for redistribution. The definitive version was published in Radiocarbon 52 (2010): 1322-1335.
Description:
The Keck Carbon Cycle AMS facility at the University of California, Irvine (KCCAMS/UCI) has developed
protocols for analyzing radiocarbon in samples as small as ~0.001 mg of carbon (C). Mass-balance background corrections
for modern and 14C-dead carbon contamination (MC and DC, respectively) can be assessed by measuring 14C-free and modern
standards, respectively, using the same sample processing techniques that are applied to unknown samples. This approach
can be validated by measuring secondary standards of similar size and 14C composition to the unknown samples. Ordinary
sample processing (such as ABA or leaching pretreatment, combustion/graphitization, and handling) introduces MC contamination
of ~0.6 ± 0.3 μg C, while DC is ~0.3 ± 0.15 μg C. Today, the laboratory routinely analyzes graphite samples as small
as 0.015 mg C for external submissions and ≅0.001 mg C for internal research activities with a precision of ~1% for ~0.010
mg C. However, when analyzing ultra-small samples isolated by a series of complex chemical and chromatographic methods
(such as individual compounds), integrated procedural blanks may be far larger and more variable than those associated with
combustion/graphitization alone. In some instances, the mass ratio of these blanks to the compounds of interest may be so
high that the reported 14C results are meaningless. Thus, the abundance and variability of both MC and DC contamination
encountered during ultra-small sample analysis must be carefully and thoroughly evaluated. Four case studies are presented
to illustrate how extraction chemistry blanks are determined.
Repository Name:
Woods Hole Open Access Server
Type:
Article
Format:
application/pdf
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