Fractionation in the graphitization reaction for 14C-AMS analysis: The role of Zn × the role of TiH2

Abstract Isotopic fractionation in the graphitization reaction for Radiocarbon Accelerator Mass Spectrometry measurements was evaluated. At LAC-UFF we use the TiH 2 /Zn reduction method, where H 2 and Zn enable the reduction of CO 2 into graphite. In previous works, we analyzed C stable isotopes ratio for different amounts of Zn in the range of 0–50 mg and the results indicated that the amount of Zn is strongly linked to both the degree and variability of isotopic fractionation during the reaction when the quantity of TiH 2 ranges from 10 to 15 mg for samples containing between 0.7 and 1.0 mg of C. For no changes in fractionation have occurred by increasing the graphitization temperature from 520 °C to 550 °C, in the present paper we evaluate the effects of different temperatures for the H 2 release step. Previous works have also led us to question the role of Zn in the TiH 2 -based process and how it affects fractionation. Therefore, graphitization reactions without TiH 2 or without Zn, using different amounts of TiH 2 , were tested. The former reaction has required values of Zn:C > 50 while the latter is not recommended. When Zn:C = 30, minimum amounts of TiH 2 (TiH 2 :C