Analysis of lipsticks by ART FT-IR microspectroscopy

Abstract

The slide-on Ge µIRE and the slide-on diamond µIRE for ATR FT-IR spectral acquisition with an infrared microscope were employed for molecular characterization of trace lipstick smear on various surfaces. Due to the small sampling area of the IREs, a small quantity of lipsticks can be analyzed. The spectra acquired by diamond µIRE and Ge µIRE were in good agreement to those acquired by conventional ATR technique. In this work, commercial lipsticks from various manufactures were investigated. Direct correlation between the molecular structures and the infrared absorptions enable the identification of lipstick based on the observed ATR FT-IR spectra of the trace lipstick smear. The “contact-and-collect” operation was employed for transferring the trace lipstick onto the tip of the IREs. A minute smear of lipstick on the μIRE can be analyzed while the chemical information of lipsticks on various substrates was obtained without any interference from the substrate. The operation was non-destructive and could be performed without an additional sample preparation. This method is suitable for the unique identification of minute lipstick amount as well as forensic analysis.