Improved method for analysing lipstick samples could help solve crime
The project, which was presented at the 251st National Meeting & Exposition of the American Chemical Society (ACS), began to improve forensic analysis for crime scene investigations, as lipstick has often been an aide in solving cases.
The main problem with the current methods, according to the team at Western Illinois University, is that, unlike the instant result that TV and the movies would have you believe, forensic analysis can take a while and can be a complicated process.
The current methods involve difficult or expensive steps such as a tedious lipstick removal process or examination of samples by Raman spectroscopy or X-ray diffraction, and these require specialised equipment and training, which are in short supply in under-funded and over-worked forensics labs.
The research team thus decided to develop a better way to lift these samples and further analyse them, beginning with an established method of lipstick sample extraction, but then eliminated unnecessary steps and improved upon the rest.
The final method is a two-part process: First they add an organic solvent to remove most of the oils and waxes, and then they add a basic organic solvent to extract the remaining residue.
“Right now we are just lifting samples off of paper, but in the future we are hoping to use different articles and media that could be found at a crime scene,” says Brian Bellott, PhD at the university.
Study methods
In their study, to avoid methods that involve complex training, the team investigated three types of chromatography: thin layer chromatography (TLC), gas chromatography (GC) and high performance liquid chromatography (HPLC).
GC and HPLC methods both rely on injecting a sample into a machine and reading the results on a computer, whereas TLC involves researchers looking at samples on a special type of surface under ultraviolet light.
The team chose 40 lipsticks and made marks with them on paper to simulate finding smears at the scene of a crime.
Different brands of lipsticks have unique compositions of organic molecules, which give distinct chromatography signals. This meant the researchers could then compare the spectra of crime scene lipstick to those of known lipsticks, which are compiled in a database.
Once the brand is identified, law enforcement officials could investigate whether a suspect uses that particular cosmetic.
The team is still performing the analyses, but at this stage they see the best results with the GC technique.
Bellott says this overall method, from sample gathering to analysis, can be adopted by forensic labs as-is. However, the team is working on making it even better by continuing to build their extensive lipstick library and looking for ways to make it easier and more robust.
