Lipsticks, due to their easy transfer and widespread use, can provide important evidence in crime investigations, in particular in cases of rape, murder or burglary. Discrimination between and identification of lipstick samples is a challenge because of their similar chemical composition. The main components of lipsticks – oils and waxes – are a difficult matrix to analyse. Furthermore, lipsticks contain various additional compounds, both ionic and neutral. A promising approach to the examination of lipstick traces is the use of microemulsion electrokinetic capillary chromatography (MEEKC). In order to optimize the MEEKC method, a series of mixtures of dye standards in various microemulsions (MEs) (differed in qualitative and quantitative composition) and measurement conditions were analysed. The influence of the type and pH of the buffer, the type and amount of surfactant and oil phase, as well as the effect of the addition of a second surfactant, organic solvent and cyclodextrin, were investigated. The ME with the best separation properties contained 3% SDS, 6% butanol and 0.8% n-octane (w/w) in a borate buffer at pH 10. Short-end mode enabled the separation to be reduced to less than 4 min. Ultrasound-assisted extraction (UAE) performed for 10 min at 25 °C was found to be the most effective for real lipstick samples preparation. The developed UAE-MEEKC method was verified in terms of precision (RSDtm for real samples analysed in one day was < 2.2%, and over three days was < 3.0%) and successfully used for the discrimination of six red lipsticks.
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Król et al. (2020) studied this question.