Emily C. Lennert
trace, evidence, glitter, particle, Fourier transform, infrared, spectroscopy, FT-IR, IR, synchrotron
Article to be reviewed
- Vernoud, L.; Betchel, H. A.; Matrin, M. C.; Reffner, J. A.; Blackledge, R. D. Characterization of multilayered glitter particles using synchrotron FT-IR microscopy. Forensic Science International. 2011, 210, 47-51.
The opinions expressed in this review are an interpretation of the research presented in the article. These opinions are those of the summation author and do not necessarily represent the position of the University of Central Florida or of the authors of the original article.
Glitter, whether from clothing, cosmetics, or other sources, may serve as an important form of associative evidence. Glitter is easily transferred between items and retained due to its small particle size. While glitter is commonly considered mass produced with little difference, by identifying was to characterize and differentiate glitter samples, it may become useful as a form of evidence. Characterization of glitter may include the examination of a glitter particle’s color, size, thickness, shape, and chemical profile. The number of layers and relative thickness of the layers also provides characteristic information about the glitter particle. Some layers may be as small as <10μm thick, and traditional Fourier transform – infrared spectroscopy (FT-IR) may not be capable of obtaining the infrared spectrum of such a thin layer. To address this, synchrotron FT-IR is used. Synchrotron infrared light is a light source that is 100-1,000 times brighter than traditional infrared light sources, which results in imaging with high spatial resolution. Spatial resolution refers to the pixel size in an image; images with better spatial resolution will have smaller pixels which provides a clearer picture. Due to its high spatial resolution, synchrotron FT-IR is capable of obtaining spectra from the very thin layers of glitter particles. Using synchrotron FT-IR, the authors of this paper were able to characterize glitter by imaging cross-sections of glitter particles, counting the layers in the particle, and obtaining IR spectra of individual layers in multilayered glitter particles.
Glitter particles were cross-sectioned with a microtome for analysis. Four particles were characterized. In the first particle, seven layers were observed. Infrared spectra were used to create a heat map, which was overlaid on an image of the glitter particle, as seen in Figure 1 a) within the study. In the heat map, the seven layers can be clearly seen and show that this glitter particle is symmetrical in composition, with four chemically distinct regions making up the seven layers. The particle was measured to be 130 μm thick, contrasting the manufacturer’s stated thickness of 26-36 μm. The thickness difference may be due to the microtome process, in which the particle may swell to a larger size or become distorted from cutting, or the glitter particle may in fact be thicker than stated by the manufacturer.
The second glitter sample contained the most layers, with 7 layers identified through the heat mapping of the intensity of the CH3:CH2 ratio. The CH3:CH2 ratio is determined by the ratio of the peak area at 2990 cm-1 and 2960 cm-1, respectively. However, inclusion of additional spectral data, namely the peaks at 1780 cm-1 and 1341 cm-1, revealed 11 chemically distinct layers within the particle, illustrated in Figure 2 c) within the study. Again, the particle appeared to have a symmetrical layering pattern. The cross section width was determined to be 139 μm, while the manufacturer reported a width of 26-36 μm. Again, this may be due to swelling or distortion.
Although more layers appear to be present in visual analysis, only five chemically distinct layers were observed in particle 3, based on spectral analysis. In examining the CH3:CH2 ratio, layers 1, 3, and 5 were determined to be similar to one another, but distinct from layers 2 and 4. Inclusion of the full spectra revealed five chemically distinct layers. The cross section width was determined to be 101 μm, while the manufacturer indicated a width of 28-36 μm. This discrepancy may be due to swelling or distortion, as previously discussed.
Glitter particle 4 was observed to be an asymmetrical particle. Visually, three layers were observed, while the spectra appeared similar across the three layers. However, examination of the CH3:CH2 ratio and the CH region of the spectra revealed three chemically distinct layers. The cross section width was measured to be 49 μm, much closer to the manufacturer’s reported width of 33-36 μm compared to previous samples.
- Glitter particles are composed of multiple layers which may be chemically distinct from one another.
- Synchrotron FT-IR offers a technique for analyzing individual layers of glitter particles.
Glitter is a valuable form of trace evidence. The characterization and classification of glitter increases its value as associative evidence.
This study may serve as a proof of concept, providing the basis for glitter characterization and classification by synchrotron FT-IR.