New way to read lipstick in crime

Scientists have developed a new method for lifting and analysing lipstick smears from surfaces at crime scenes, which may help forensic teams identify the brand of the cosmetic and narrow down on suspects.

For years, forensic scientists have applied various methods to remove lipstick samples from crime scenes and analyse their chemical constituents. Many 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.

However, these methods require specialised equipment and training, which are in short supply in under-funded and over-worked forensics labs. Researchers at Western Illinois University in US decided to develop a better way to lift these samples and further analyse them.

They began 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,” said Brian Bellott.

Armed with a short, robust way to lift lipstick, the team turned to determining a quick, efficient method for analysing the cosmetic. 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. Then researchers can compare spectra of crime scene lipstick to those of known lipsticks, which are compiled in a database, or “library.” 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.