Forensic Analysis of Eyeshadows using ATR-FTIR Spectroscopy and Chemometrics

Abstract

Eye cosmetics, like eyeshadows, are commonly used and easily transferred, making them potential crucial trace evidence at crime scenes. This study focuses on resolving criminal cases by connecting victims, suspects, and crime scenes through the analysis of eyeshadow. Conventional methods like flame atomic absorption spectroscopy and x-ray fluorescence are destructive, hindering forensic examination. Instead, this research employs attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy coupled with chemometric methods like principal component analysis (PCA) and principal component analysis-linear discriminant analysis (PCA-LDA). ATR-FTIR spectroscopy reveals compositional variations among eyeshadows, with unique peaks representing functional groups. PCA aids in pattern recognition, and PCA-LDA achieves 100% calibration accuracy and 45% validation accuracy for brand differentiation. However, a preliminary substrate study suggests challenges in analyzing eyeshadows on materials like cotton cloth and glass, leading to difficulties linking stains to their source. The study aims to establish a non-destructive, rapid, and reproducible method for the forensic analysis of eye cosmetics using ATR-FTIR spectroscopy, contributing to the understanding and application of this technique in forensic science.