Biological/Biomedical Accelerator Mass Spectrometry Targets. 2. Physical, Morphological, and Structural Characteristics

• Published in: Analytical chemistry (Washington) 2008-10, Vol.80 (20), p.7661-7669
• Main Authors: Kim, Seung-Hyun, Kelly, Peter B, Clifford, Andrew J
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Biomedical materials; Chemistry; Color; Diffraction; Exact sciences and technology; Graphite - chemistry; Iron; Iron - chemistry; Mass spectrometry; Mass Spectrometry - methods; Methods; Microscopy, Electron, Scanning; Nanocrystals; Sensitivity and Specificity; Spectrometric and optical methods; Spectrum Analysis, Raman; Temperature; X-Ray Diffraction; X-rays
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac801228t

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 (F m). 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 nanocrystalline 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, Raman, or XRD, matched exactly those of the graphite standard. Nevertheless, AMS targets of GCIP consistently produced the strong, reliable, and reproducible ion currents for high-throughput AMS analysis (270 targets per skilled analyst/day) along with accurate and precise F m values.