Application of zinc sealed tube graphitization on sub-milligram samples using EnvironMICADAS

The aim of this study was to extend the utilization range of our sealed tube graphitization methods toward the microgram sample sizes on EnvironMICADAS accelerator mass spectrometer in the Institute for Nuclear Research of the Hungarian Academy of Sciences, Hertelendi Laboratory of Environmental Studies (ATOMKI HLES). To accomplish this purpose both methods, which are routinely used in ATOMKI HLES (TiH2-Zn-method and Zn-method) have been tested in the range of 25-250 μg carbon content. To exclude the side effects caused by the possible contamination by the chemical pretreatment and combustion of small samples, all micro-graphite targets have been produced by splitting CO2 gas from combusted samples containing 1 mg C and radiocarbon free fossil CO2 without any chemical preparation. The result of the comparison was that the Zn-method produces lower blank levels in the range of 25-100 μg carbon content than the combined TiH2-Zn method. For this reason, the Zn-method has been used for further optimization of the parameters of graphitization of samples with 25 μg carbon content. Based on the executed tests the optimal graphitization parameters for 25 μg carbon content are 2.5 mg iron catalyst, 2.5 mg zinc reagent and 450 °C graphitization temperature. With these parameters 3.1 ± 0.1 pMC average background level can be reached (based on measurement of 12 Zn-method target) and the available precision for modern samples was 0.9-1.0% using EnvironMICADAS.