Roberts Mark L.

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Roberts
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Mark L.
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  • Article
    Single Step Production of Graphite from Organic Samples [Poster]
    ( 2017) Elder, Kathryn L. ; Roberts, Mark L. ; Lardie Gaylord, Mary C.
    We present a low-cost, high-throughput method for converting many types of organic samples into graphite. The method combines sample combustion and graphitization in a single process. Using a modified sealed graphitization method, samples are placed in a Pyrex tube containing zinc, titanium hydride and iron catalyst. The tube is evacuated, flamed sealed, and placed in a muffle furnace for 7 hours. Graphite forms on the iron and is then analyzed for 14C content using either of NOSAMS’s two AMS systems. This method has been shown to work on a variety of organic samples including pure compounds, wood, peat, collagen and humics. This simplified procedure could be especially useful in reconnaissance studies in which it is desired to rapidly measure a large number of samples (untreated or pretreated), at low-cost with analytical precision and accuracy approaching that of traditional hydrogen reduction methods.
  • Article
    Ultra-small graphitization reactors for ultra-microscale 14C analysis at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) Facility
    (University of Arizona Libraries, 2015) Shah Walter, Sunita R. ; Gagnon, Alan R. ; Roberts, Mark L. ; McNichol, Ann P. ; Lardie Gaylord, Mary C. ; Klein, Elizabeth
    In response to the increasing demand for 14C analysis of samples containing less than 25 µg C, ultra-small graphitization reactors with an internal volume of ~0.8 mL were developed at NOSAMS. For samples containing 6 to 25 µg C, these reactors convert CO2 to graphitic carbon in approximately 30 min. Although we continue to refine reaction conditions to improve yield, the reactors produce graphite targets that are successfully measured by AMS. Graphite targets produced with the ultra-small reactors are measured by using the Cs sputter source on the CFAMS instrument at NOSAMS where beam current was proportional to sample mass. We investigated the contribution of blank carbon from the ultra-small reactors and estimate it to be 0.3 ± 0.1 µg C with an Fm value of 0.43 ± 0.3. We also describe equations for blank correction and propagation of error associated with this correction. With a few exceptions for samples in the range of 6 to 7 µg C, we show that corrected Fm values agree with expected Fm values within uncertainty for samples containing 6–100 µg C.