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Fundamentals of Forensic Pigment Identification by Raman Microspectroscopy: A Practical Identification Guide and Spectral Library for Forensic Science Laboratories

NCJ Number
Date Published
November 2011
572 pages
This project conducted basic research in Raman spectroscopy that is needed to begin an evaluation of the potential benefits and evidentiary significance that Raman spectroscopy can provide to the forensic community.
The concept of Raman scattering is based on a laser that is focused onto a sample, typically in a 1-2 mm spot. A small fraction of this energy is inelastically scattered by molecules in the sample. The scattering results from the interaction of the monochromatic photons with molecular vibrations in the sample. As a result, the scattered photons have shifted in energy by an amount characteristic of a particular molecular vibration. The scattered light is collected by an objective (in a microscope system), projected onto a diffraction grating (in a dispersive system), and the scattered light is projected onto an energy calibrated CCD. The resulting spectrum is measured in wavenumbers, but relative to the energy of the laser. The abscissa of a Raman spectrum is denoted as a Raman shift, and is plotted in delta wavenumbers. The development of Raman microspectroscopy has opened a new approach in the identification of pigments in a consistent and reliable manner. The speed, minimal sample preparation requirements and power to identify a wide range of compounds suggest that Raman spectroscopy will gain more and more use in forensic laboratories as applications are developed. This project developed the most thorough spectral pigment database that currently exists; conducted supporting analyses to determine that the analyzed pigments were consistent with their labels; and developed an objective Quality Index for ranking the provenance of a pigment sample; developed a pigment classification scheme that enables interpretation of pigment evidence; and created the current manual for forensic practitioners as a guide for the development and use of Raman spectroscopy as an analytical method in forensic laboratories. References and bibliography and appended list of pigments, Raman spectra of pigments, pigment chemical categories, and pigment classification scheme

Date Published: November 1, 2011