Non-destructive characterisation of lip cosmetics using attenuated total reflectance fourier-transform infrared spectroscopy with chemometrics

Abstract

Lip cosmetics present a challenging identification and differentiation of lip cosmetics in forensics, given their similar chemical compositions, particularly within the same colour category. The authors utilised attenuated total reflection spectroscopy and chemometrics to analyse 30 brown lip cosmetic samples across five categories: lip crayons, lip glosses, liquid lipsticks, lip pencils, and solid lipsticks. The major findings observed in the analysis of lip cosmetics included weak intensity spectra for key functional groups such as hydroxy, aliphatic, carbonyl-containing species, and ether. In addition, the hierarchical cluster analysis grouped most samples into two main clusters: lip crayons and most solid lipsticks in one, and most lip glosses, liquid lipsticks, and lip pencils. Principal component analysis revealed clear clusters of lip glosses, liquid lipsticks, and lip pencils, with scattered lip crayons and solid lipsticks. Furthermore, trace analyses yielded limited results, with only one trace (TR3T) showing similarity to the lip gloss (LG2) spectrum. This study sheds light on the complexities surrounding the differentiation of lip cosmetics. Further studies should study several types of lip cosmetics with varying shades and analyse their traces on different substrates to produce accurate, reliable, and generalised outcomes. These findings emphasise the need for more comprehensive investigations to enhance forensic analytical approaches.