Raman spectroscopy analyzes lipstick traces non-destructively

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Forensic scientists at the University of Kent in England have established a new way of identifying which brand of lipstick someone was wearing at a crime scene without removing the evidence from its bag, thereby avoiding possible contamination.

Using Raman spectroscopy, forensic investigators will be able to analyze lipstick marks left at a crime scene, such as on glasses, a tissue, or cigarette butts, without compromising the continuity of evidence as the sample will remain isolated. 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. Current analysis of lipstick traces relies on destructive forensic techniques or human opinion.

"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," explains Professor Michael Went of the Universityâs School of Physical Sciences. "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 analyzed quickly and non-destructively."

Raman spectroscopy is a process involving light and vibrational energy of chemical bonds. When a material--in this case, lipstick--scatters light, most of the light is scattered at its original wavelength, but a very small proportion is scattered at altered wavelengths due to changes in vibrational energy of the materialâs molecules. This light is collected using a microscope to give a Raman spectrum, which gives a characteristic vibrational fingerprint that can be compared to spectra of lipsticks of various types and brands. Therefore, it is possible to determine identity of the lipstick involved.

Research into applying the same method on other types of cosmetic evidence, such as foundation powders, eyeliners, and skin creams, is also underway.

Full details of the work are published in the journal Analytical Methods; for more information, please visit http://pubs.rsc.org/en/Content/ArticleLanding/2013/AY/C3AY41274A.

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