Differentiation of red lipsticks using the attenuated total reflection technique supported by two chemometric methods.

The main challenge for the identification and differentiation of lipsticks for forensic purposes is the fact that they have a similar chemical composition - in particular, samples of the same hue. The objective of the presented research was to solve this problem using a nondestructive analytical technique - attenuated total reflection spectroscopy (ATR). 38 red lipsticks produced by 20 different manufacturers were examined in optimized experimental conditions. To facilitate discrimination and provide more extensive analyses of the obtained data, two chemometric techniques: principal component analysis and cluster analysis were used. Ultimately, nine groups of investigated lipstick samples with comparable chemical compositions were differentiated. Moreover, lipstick smears on six different interfering surfaces were analyzed and spectral subtraction was performed in order to identify individual samples. The established approach succeeded in identifying the index number and the manufacturer of the samples by using an in-lab built ATR spectra library. The developed method demonstrates a great potential for the differentiation and identification of red lipsticks with a very similar hue. It also seems to have good prospects for future application in forensic science investigations.