Anal. Chem. 2008, 80, 7661–7669 Biological/Biomedical Accelerator Mass Spectrometry Targets. 2. Physical, Morphological, and Structural Characteristics Seung-Hyun Kim,† Peter B. Kelly,‡ and Andrew J. Clifford†,* Department of Nutrition and Department of Chemistry, University of California Davis, One Shields Avenue, Davis, California 95616 The number of biological/biomedical applications that require AMS to achieve their goals is increasing, and so is the need for a better understanding of the physical, morphological, and structural traits of high quality of AMS targets. The metrics of quality included color, hardness/ texture, and appearance (photo and SEM), along with FT- IR, Raman, and powder X-ray diffraction spectra that correlate positively with reliable and intense ion currents and accuracy, precision, and sensitivity of fraction modern (Fm). Our previous method produced AMS targets of gray- colored iron-carbon materials (ICM) 20% of the time and of graphite-coated iron (GCI) 80% of the time. The ICM was hard, its FT-IR spectra lacked the sp2 bond, its Raman spectra had no detectable G′ band at 2700 cm-1, and it had more iron carbide (Fe3C) crystal than nanoc- rystalline graphite or graphitizable carbon (g-C). ICM produced low and variable ion current whereas the opposite was true for the graphitic GCI. Our optimized method produced AMS targets of graphite-coated iron powder (GCIP) 100% of the time. The GCIP shared some of the same properties as GCI in that both were black in color, both produced robust ion current consistently, their FT-IR spectra had the sp2 bond, their Raman spectra had matching D, G, G′, D+G, and D′′ bands, and their XRD spectra showed matching crystal size. GCIP was a powder that was easy to tamp into AMS target holders that also facilitated high throughput. We concluded that AMS targets of GCIP were a mix of graphitizable carbon and Fe3C crystal, because none of their spectra, FT-IR, Ra- man, or XRD, matched exactly those of the graphite standard. Nevertheless, AMS targets of GCIP consistently produced the strong, reliable, and reproducible ion cur- rents for high-throughput AMS analysis (270 targets per skilled analyst/day) along with accurate and precise Fm values. Graphitization of solid carbon of biological/biomedical origin is a two-step process: ﬁrst the carbon of a sample of interest is oxidized to CO2, and second, the CO2 is then reduced to graphitic materials. Graphite is a well-ordered crystal structure of carbon * To whom correspondence should be addressed: E-mail: ajclifford@ucdavis.edu. Tel: 530-752-3376. Fax: 530-752-8966. † Department of Nutrition. ‡ Department of Chemistry. 10.1021/ac801228t CCC: $40.75  2008 American Chemical Society Published on Web 09/12/2008 that is classiﬁed as natural or synthetic.1,2 The H2 or Zn reduction method has long been used for carbon dating and more recently for biological/biomedical AMS applications.3-9 A variety of terms such as amorphous carbon (a-C),10 graphite,5 a fullerene “graph- ite”,6 or solid fullerene11 have been used within and between prior reports to describe the material produced during the reduction of CO2, CO, or both. While the physical, morphological, and structural characteristics of the AMS targets that had been produced seemed to vary within and between reports, they have not been studied systematically nor has the importance of their physical, morphological, and structural characteristics in maximiz- ing ion current been well determined. Using Zn as the reductant, Jull et al.12 ﬁrst reported the formation of a mix of well-crystallized materials, poorly crystallized materials, and on occasion, a metal carbide (MeC). While nickel formed a different (more compli- cated) MeC compared to cobalt or iron,4 MeC, in general, failed to produce a robust ion current so the ratios of 14C/13C varied by as much as 10% among replicate analyses.5 Therefore, in the present paper, we describe the color, hardness, texture, scanning electron microscopy (SEM), FT-IR transmission, Raman spectrometry, and XRD analyses of the accelerator mass spectrometry (AMS) targets (carbon material that coated over the -400 mesh spherical iron powder, -400MSIP) as prepared by our previous7 and optimized13 methods. Our goal (1) Oya, A.; Marsh, H. J. Mater. Sci. 1982, 17, 309–322. (2) Wissler, M. J. Power Sources 2006, 156, 142–150. (3) Vogel, J. S.; Southon, J. R.; Nelson, D. E.; Brown, T. A. Nucl. Instrum. Methods Phys. Res., Sect. B 1984, 5, 289–293. 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