Blank assessment for ultra-small radiocarbon samples: chemical extraction and separation versus AMS

TLDR: 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 ~0001 mg of carbon (C) Mass-balance background corrections for modern and 14C-dead carbon contamination (MC and DC) were assessed by measuring 14C free and modern standards, respectively, using the same sample processing techniques that are applied to unknown samples as discussed by the authors.

Abstract: 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 ~0001 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 ~06 ± 03 μg C, while DC is ~03 ± 015 μg C Today, the laboratory routinely analyzes graphite samples as small as 0015 mg C for external submissions and =0001 mg C for internal research activities with a precision of ~1% for ~0010 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