CSI Technique Avoids Forensic Evidence Contamination
August 9, 2013

Forensic Raman Spectroscopy Can Analyze Lipstick Traces Without Contamination

April Flowers for redOrbit.com - Your Universe Online

One of the chief concerns at any crime scene investigation is avoiding contamination of forensic evidence. A new study by forensic scientists at the University of Kent, UK, has established a new method of identifying the brand of lipstick someone was wearing at a crime scene without removing the evidence from its bag.

The researchers used a technique called Raman spectroscopy that detects laser light. This technique will allow forensic investigators to analyze lipstick marks left at a crime scene, such as on glasses, a tissue or cigarette butts, without compromising the continuity of evidence because the sample will remain isolated.

Physical contact between two individuals – such as victim and suspect – can be established by analysis of lipstick traces found at the scene. The analysis can also be used to place an individual at a crime scene. Current analysis requires destructive forensic techniques or human opinion, making the new method particularly significant.

Professor Michael Went of the University’s School of Physical Sciences said, “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. 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.”

The process of Raman spectroscopy involves light and the vibrational energy of chemical bonds. When lipstick, or any material, scatters light, most of it is scattered at its original wavelength. A very small proportion, however, is scattered at altered wavelengths due to changes in vibrational energy of the material’s molecules. This altered light is collected using a microscope to give a Raman spectrum. This spectrum gives a characteristic vibrational fingerprint which can be compared to a spectra of lipsticks of various types and brands, making it possible to identify the lipstick without destructive methods.

The research team is continuing their study by applying the same method on other types of cosmetic evidence, such as foundation powders, eye-liners and skin creams.

The findings of this study were published in the journal Analytical Methods.