Forensic analysis of red lipsticks using ATR-FTIR spectroscopy and chemometrics

Lipsticks are used on routine basis, and due to its prevalence, it can be encountered at the crime scene as trace transferred evidence. Analyses of such exhibits can provide corroborative evidence to link the suspect with the victim or with the crime scene. In the present study, 38 different red shade lipsticks of 20 different manufacturers were analyzed using ATR-FT-IR (attenuated total reflectance-Fourier transform-infrared) spectroscopy. Chemometric methods: PCA (principal component analysis) and PCA-LDA (linear discriminant analysis), applied to provide objective interpretation of results resulted in 100% discriminating power and 81.48% correct classification respectively. The effects of different substrates on lipstick analyses, lipstick wear time for one day, and exposure to different environmental conditions were also studied. More research is required for linking lipstick smudges on different substrates with their source of origin using chemometric methods.