Graphitization of Samples Containing Sulfur and Chlorine Using the Sealed Tube Zinc Reduction Method for 14C Analysis on AMS
Dr Xiaomei Xu1, Connor J. Mateer1, Hector Martinez De La Torre1
1Department of Earth System Science, University of California Irvine, , United States
The method of graphitization by sealed tube zinc reduction of sample CO2 to filamentous graphite has been shown to provide reliable 14C measurements using AMS with low backgrounds and high precision, and over a wide range of sample sizes (1 mgC to <15 µgC) [1-3]. One advantage of this method is that graphite can be stored inside of the tube until the AMS 14C measurements can be performed. We report here an additional advantage of the method – to be able to graphitize samples containing Sulfur (S) and Chlorine (Cl).
It’s well documented that it’s problematic for Sulfur (S) contained organic samples in graphitization using the H2 reduction method because S can interfere with the graphitization, thus S is considered “poison” to the H2 reduction graphitization. Very often silver is added to combustion of organic samples, especially samples formed in reduced environment to remove S as Ag2S. If S content is high additional separation step is needed to ensure complete S removal before graphitization.
We have investigated graphitization of various C sizes of samples with up 21.5%S, such as methionine (C5H11NO2S), without separating S beforehand. For a full size sample of 0.7-0.9 mgC, the S amount can be as high as 0.48 mgS in combustion. Graphitization of pure 1mgC-aminio acids with various amount of NaCl added has also been investigated and shown successful graphitization up to 100mg NaCl added in combustion with Pyrex glass tube. During the sealed tube Zn reduction graphitization, S and Cl are expected to form ZnS and ZnCl2 respectively, and do not interfere with the graphite forming. Silver is not needed in combustion of all organic samples, which reduces the cost and C blank in the process. The graphite produced from S and Cl contained samples perform well in the ion source of our AMS at UCI, in terms of beam currents and precision.
 X. Xu, S.E. Trumbore, S.H. Zheng, J.R. Southon, K.E. McDuffee, M. Luttgen, J.C. Liu, Modifying a sealed tube zinc reduction method for preparation of AMS graphite targets: Reducing background and attaining high precision, Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms, 259 (2007) 320-329. https://doi.org/10.1016/j.nimb.2007.01.175
 M.S. Khosh, X. Xu, S.E. Trumbore, Small-mass graphite preparation by sealed tube zinc reduction method for AMS C-14 measurements, Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms, 268 (2010) 927-930. https://doi.org/10.1016/j.nimb.2009.10.066
 B.D. Walker, X. Xu, An improved method for sealed tube zinc graphitization of microgram carbon samples for AMS 14C measurement, Nucl. Instr. Meth. Phys. Res. Sect. B 438 (2019) 58-65. https://doi.org/10.1016/j.nimb.2018.08.004
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