Lip sync: Raman raises brand awareness

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  • Published: Sep 1, 2013
  • Author: David Bradley
  • Channels: Raman
thumbnail image: Lip sync: Raman raises brand awareness

Lipstick on your collar?

Forensic scientists in the UK have demonstrated that Raman spectroscopy can be used to identify the specific brand of lipstick someone was wearing at a crime scene without removing the evidence from its bag and so avoid possible cross-contamination and ensuring a secure prosecution.

Forensic scientists in the UK have demonstrated that Raman spectroscopy can be used to identify the specific brand of lipstick someone was wearing at a crime scene without removing the evidence from its bag and so avoid possible cross-contamination and ensuring a secure prosecution.

Raman spectroscopy can now be used to analyse lipstick traces left at a crime scene on a drinking vessel, tissue or cigarette butt, for instance. The analysis is entirely non-invasive and can be done while the evidence remains "bagged" so its chemical and physical integrity are not compromised by handling or destructive analytical techniques, for example. Analysis of lipstick traces from crime scenes can be used to establish physical contact between two individuals, such as a victim and a suspect, or to place an individual at a crime scene, whether witness, victim or perpetrator of said crime. The new technique is particularly significant for forensic science as current analysis of lipstick traces relies on destructive forensic techniques or human opinion.

Please don't touch

"Continuity of evidence is of paramount importance in forensic science and can be maintained if there is no need to remove it from the bag," says Kent University's Michael Went, who worked with Fatma Salahioglu and Stuart Gibson on the research. Raman spectroscopy is ideal as it can be performed through transparent layers, such as evidence bags. For forensic purposes Raman spectroscopy also has the advantages that microscopic samples can be analysed quickly and non-destructively.

Lipstick is a cosmetic product containing pigments, oils, waxes, and emollients that apply colour, texture, and protection to the lips. There are many varieties and the term might also refer to other related products that are used to apply a gloss or colour cosmetically. Colour matching can be done by eye, while thin layer chromatography is commonly used to separate components for identification. These are both subjective and require debagging. Raman scattering from a lipstick sample allows the forensic scientists to obtain a characteristic pattern from a piece of evidence that can then be matched to other suspect samples or to a database of brands.

Cosmetic forensic

The team points out that a range of excitation wavelengths (473, 633 and 784 nanometres) was adequate for overcoming various problems including testing fluorescent lipstick samples and that the forensic "medium" - tissue paper, textile fibres, glass, cigarette - made little difference to the analysis. Moreover, most samples gave spectra unchanged even after the samples were aged for two years, although for some samples one or two peaks lost intensity or disappeared altogether.

The team explored the chemometrics potential for characterisation of large numbers of lipstick spectra using thirty spectra from ten different lipsticks and analyzing the data using principal components analysis (PCA) and classifying them using the k-Nearest Neighbours (kNN) classifier. They were able to garner 98.7% accuracy in classifications.

The team is currently investigating how the same spectroscopic approach might be applied to other cosmetic evidence, such as skin-toned foundation powders, eye-liners and skin creams all of which have chemical profiles peculiar to particular brands and types or can be readily matched to samples obtained from other crime scenes, suspects or witnesses.

"We would also like to apply spectroscopic methods to the rapid detection of counterfeit goods," Went told SpectroscopyNOW. "We have ongoing interests in the detection of trace evidence by Raman spectroscopy, for example, traces of drugs found in fingerprints."

Related Links

Analyt Methods 2013, online: "Application of Raman spectroscopy for the differentiation of lipstick traces"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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