Quality of Graphite Target for Biological/Biomedical/Environmental Applications of ¹⁴C-Accelerator Mass Spectrometry

Abstract

Catalytic graphitization for 14C-accelerator mass spectrometry (14C-AMS) produced various forms of elemental carbon. Our high-throughput Zn reduction method (C/Fe = 1:5, 500 °C, 3 h) produced the AMS target of graphite-coated iron powder (GCIP), a mix of nongraphitic carbon and Fe3C. Crystallinity of the AMS targets of GCIP (nongraphitic carbon) was increased to turbostratic carbon by raising the C/Fe ratio from 1:5 to 1:1 and the graphitization temperature from 500 to 585 °C. The AMS target of GCIP containing turbostratic carbon had a large isotopic fractionation and a low AMS ion current. The AMS target of GCIP containing turbostratic carbon also yielded less accurate/precise 14C-AMS measurements because of the lower graphitization yield and lower thermal conductivity that were caused by the higher C/Fe ratio of 1:1. On the other hand, the AMS target of GCIP containing nongraphitic carbon had higher graphitization yield and better thermal conductivity over the AMS target of GCIP containing turbostratic carbon due to optimal surface area provided by the iron powder. Finally, graphitization yield and thermal conductivity were stronger determinants (over graphite crystallinity) for accurate/precise/high-throughput biological, biomedical, and environmental14C-AMS applications such as absorption, distribution, metabolism, elimination (ADME), and physiologically based pharmacokinetics (PBPK) of nutrients, drugs, phytochemicals, and environmental chemicals.

Accuracy and precision of <sup>14</sup>C-based source apportionment of organic and elemental carbon in aerosols using the Swiss_4S protocol

“…The production of high quality, uniform graphite targets, suitable for the AMS ion source, is important for the optimal performance of any AMS system. The quality of the graphite influences the level of background contamination, the mass fractionation, and the beam current (Santos et al, 2007c, Kim et al, 2010.…”

Contamination on AMS Sample Targets by Modern Carbon is Inevitable

“…For identification of peaks, the standard reference spectra of Fe 3 C and graphite are also shown, as circles and triangles, respectively, in the GP spectrum (Downs and Hall-Wallace 2003). Kim et al (2010) measured the PXRD spectra of graphitization products with varying C/Fe mass ratio (1:1, 1:5, 1:10, and 1:15) at different temperatures (400, 500, 525 and 585°C) (Kim et al 2010). Their PXRD spectrum of the graphitization product with 1:1 (C/Fe) mass ratio, prepared at 585°C closely resembles that of the samples we prepare at 600°C (~1:1 C/Fe).…”

Biological and biomedical 14C-accelerator mass spectrometry and graphitization of carbonaceous samples

“…34 Catalytic graphitization methods for bio-14 C-AMS are known to produce a fullerene "graphite," 42,43 morphologically similar to lamentous graphite. 40 Recently, Kim et al 57,58 reported the morphological, chemical, and physical characteristics of graphite produced using their septa-sealed vial method. 37 Aer graphitization, the carbonaceous sample of interest was converted to a semi-ordered graphite-like material rather than a single graphite crystal.…”

“…In addition, they reported that the degree of graphite crystallinity did not affect 14 C-AMS analysis, including C À ion currents, bulk isotopic fractionation (d 13 C), and Modern value. 57 The ratio of carbon (graphite or graphitelike) to iron powder (used as a thermal/electrical conductor during ionization) in the graphitized sample was the most critical factor affecting reliable C À ion currents, which are required for accurate, precise, and reproducible 14 C-AMS measurements. 57 Sample type, size, graphitization yield, and other considerations for bio-14 C-AMS Table 3 shows the common biological samples used in bio-14 C-AMS and their carbon contents.…”