Applications of Raman Spectroscopy for Trace Evidence Examinations

Buzzini, P., Suzuki, E.M., Palenik, C.S., and Bowen, A.M. (2014) Applications of Raman Spectroscopy for Trace Evidence Examinations . American Academy of Forensic Sciences Annual Meeting.

A number of significant developments in commercial dispersive and Fourier transform Raman spectrometers have occurred in recent years. They include holographic gratings, CCD detector arrays, efficient notch and edge filters to remove Rayleigh scattering lines, lasers covering a very wide range of excitation wavelengths from the ultraviolet to the near-infrared regions, and microscope attachments that allow spectral data to be collected from diffraction-limited spatial areas. Consequently, Raman spectroscopy is now a mature technique that is ripe for further applications in forensic science. In view of the ability of this technique to non-destructively probe very small areas with minimal sample preparation, Raman spectroscopy has considerable potential as another tool to characterize the diverse materials encountered as trace evidence. Such evidence may consist of complex matrices for which a battery of different analytical techniques is normally applied to obtain complete information about the properties of the various components. Despite this potential and the existing literature references demonstrating such applications, Raman spectroscopy remains an underutilized technique in the forensic science laboratory. This workshop is intended to help rectify this situation.

The format of this workshop will consist of lectures in the morning and demonstrations and hands-on analyses in the afternoon. The lectures will cover various aspects of Raman spectroscopy. They include a brief theoretical background explaining the principles behind this technique, its advantages and limitations, and how the spectral data obtained by Raman spectroscopy can complement that produced by other techniques currently used for trace evidence examinations. In particular, the technique will be compared to infrared spectroscopy, as the two methods both involve transitions of molecules to higher vibrational states, although this is affected by two very different processes. The Raman spectroscopic analysis of various types of materials commonly encountered as trace evidence, including fibers, paint, cosmetics, explosives and general unknowns, will then be discussed.

For the practical exercises and demonstrations, several different commercial Raman spectrometers from different manufacturers will be available to illustrate the variety of instruments and accessories that forensic scientists can now choose from, the features of each, and the differences between them. Participants are encouraged to bring samples to the workshop for analyses.

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