The application of surface analytical techniques such as Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), and X-ray Photoelectron Spectroscopy (XPS) are explored as a means of differentiating between C-4 samples. Three different C-4 samples; U.S. military grade C-4, commercial grade C-4 (also U.S.), and C-4 from England, were obtained and analyzed using both ToF-SIMS and XPS. ToF-SIMS was able to successfully discriminate between different C-4 samples with the aid of principal components analysis (PCA), a multivariate statistical analysis approach often used to reduce the dimensionality of complex data. ToF-SIMS imaging was also used to obtain information about the spatial distribution of the various additives contained within the samples. The results indicated that the samples could potentially be characterized by their 2-D chemical structure, which varied from sample to sample. XPS analysis of the samples also showed significant variation between samples, with changes in the atomic concentrations, as well as changes in the shapes of the high resolution C(1s) and O(1s) spectra. These results clearly demonstrate the feasibility of utilizing both ToF-SIMS and XPS as tools for the direct characterization and differentiation of C-4 samples for forensic applications.
Citation: Journal of Forensic Sciences
Pub Type: Journals
SIMS, explosives, C-4, mass spectrometry, principal components analysis, imaging, XPS