14C AMS measurement and sample preparation methods of μg-sized carbon samples

14C AMS measurement and sample preparation methods for μg-sized samples have been developed at VERA. Overall measurement uncertainties do not primarily originate from the uncertainty of the AMS measurement itself, but are strongly affected by carbon contamination introduced during sample preparation. In contrast to contamination levels at graphitization, contamination introduced at earlier steps of sample preparation is sparsely investigated. At VERA, procedures with no detectable (<0.2 μg C) carbon contamination during graphitization, and contamination below 0.4 μg C during sample combustion and pretreatment were developed. Sample preparation procedures and graphitization protocols currently applied for small samples are presented. We will also discuss results of comparative AMS measurements of CO2 samples (10 μg C), either graphitized and measured at VERA or introduced as CO2 into a gas ion source installed at a MICADAS facility of the ETH Zurich. With both methods, we have reached a precision level of about 1% for 14C measurements of 10 μg C samples.