Accelerator mass spectrometry (AMS) measures the amount of the radioisotope (i.e., 14C) and compares it to the level of the stable isotope (i.e., 13C or 12C) within a sample. Absolute quantification comes from normalizing the sample's isotopic ratio to that of similarly prepared and measured standards of a known isotopic ratio. In the biosciences, 14C/C isotope ratios of biochemical samples typically range from 0.1 to 100's Modern. However, all defined primary and secondary standards used in 14C-AMS have 14C/C isotope ratios of 1.5 Modern or less, creating potential scaling problems for samples with high specific activity. We are in the process of creating carbonaceous material with 14C/C isotope ratios greater than 10 Modern, but low enough to be reliably processed and measured by AMS. This material cannot suffer from any isotopic fractionation and should consist of loose granular crystals for stability and contamination control issues. We are dissolving large quantities of oxalic acid dihydrate in water, followed by the careful addition of [14C]-oxalic acid to reach the desired 14C/C isotopic ratio. As the solution evaporates to dryness, crystals form which can then be repackaged for long term use and storage. We intend to prepare several solutions of this “hot” oxalic acid, with 14C/C isotope ratios ranging from 10 to 200 Modern. After our verification of this oxalic acid as a suitable AMS source material, we propose a roundtable with all interested parties to quantify 14C/C isotopic ratios to arrive at a consensus value. We intend to make these materials available to the AMS and, in particular, the BioAMS community for their use. This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48 and under the National Center for Research Resources Grant # RR13461.
See more of Poster Session II
See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)