Non-Destructive Forensic Discrimination of Lipstick Traces on Multiple Substrates Using ATR-FTIR and Portable Raman Spectroscopy

Lipstick traces are frequent in forensic investigations, but substrate interference and chemical similarities often challenge their interpretation. This study evaluates a non-destructive analytical workflow combining Attenuated Total Reflection Fourier transform infrared (ATR-FTIR) spectroscopy and portable Raman spectroscopy, integrated with principal component analysis (PCA) and the AGREE green metrics tool, to discriminate lipstick traces across ten forensically relevant substrates. ATR-FTIR exhibited a noticeable substrate effect; face masks showed strong spectral distortions, still allowing lipstick recognition, while other substrates masked characteristic features. Portable Raman spectroscopy improved discrimination of lipstick formulation by targeting pigment- and filler-related signals and showed reduced substrate dependence—particularly on non-porous surfaces like a plastic cup and a face mask, where surface residues retained clear spectral signatures. PCA confirmed that ATR-FTIR separation was driven by both formulation and substrate effects, whereas Raman discrimination was primarily dictated by intrinsic chemical composition. The AGREE assessment yielded high scores of 0.85 for ATR-FTIR and 0.92 for portable Raman spectroscopy, indicating excellent adherence to green analytical chemistry principles. The synergy of ATR-FTIR, portable Raman, chemometrics, and green metrics provides a rapid, non-destructive, and sustainable framework for lipstick trace analysis, enhancing discriminatory performance, forensic applicability, and environmental sustainability.