The sealed tube Zn reduction method has been applied for small-mass samples ranging from 15 to 100 μg carbon preparation for accelerator mass spectrometry (AMS) radiocarbon (14C) measurements at the AMS-14C Preparation Lab in Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (GIGCAS). The volume of the sealed reactor tube is reduced to ~0.75 cm3 in order to increase the yield of graphite. Graphite targets are measured at the Keck Carbon Cycle AMS Facility at the University of California, Irvine (KCCAMS). The targets generate a maximum 12C+1 current of about 0.5 μA per 1 μg C. The modern-carbon background is estimated to be 0.25–0.60 μg C, and dead-carbon background to be ~0.3–0.9 μg C. Both modern-carbon background and dead-carbon background are size dependent, so the results can be corrected. The precision of the small-mass modern carbon standard samples is±15–25‰ for the size of ~15–20 μg C,±5–10‰ for ~20–50 μg C, and±3–10‰ for 50–100 μg C. Further reduction of dead-carbon and modern-carbon contamination is needed in preparation of small-mass samples at GIGCAS.
