Current analytical methodologies used for examination of lipsticks and its traces for forensic purposes

Rapid and nondestructive analysis of lipstick on different substrates using ATR-FTIR spectroscopy and chemometrics

Lipstick can be an important piece of evidence in crimes like murders, rapes, and suicides. Due to its prevalence, it can be an important corroborative evidence in crime reconstruction. The analysis of such evidence can provide an evidentiary link between the suspect, the victim, object, or the crime scene. We report the use of nondestructive ATR-FTIR spectroscopy combined with chemometrics for the classification of 10 brands of lipsticks with nine samples each. Chemometric method of partial least square-discriminant analysis (PLS-DA) has been employed to interpret the data and classify the samples into their respective classes. The PLS-DA model provides an AUC figure above 0.99 in all brands except one; for which it is slightly less at 0.94. We have also tested the traces of these lipstick samples on different substrates treating them as unknowns in the already trained PLS-DA model. 100% of the samples on nine substrates viz. a cotton, nylon, plastic, dry tissue, denim (blue jeans), wet tissue, nitrile gloves, white paper, and polyester were correctly attributed to their source brand. In conclusion, the results suggest that ATR-FTIR combined with the chemometrics is a rapid, nondestructive, and accurate method for the discrimination and source attribution of lipstick. This study has potential for use in actual forensic casework conditions.

A multitechnique approach for discrimination and identification of lipsticks for forensic purposes

Cosmetics are becoming more and more popular; consequently, the chance of finding them as microtraces at a crime scene increases. They are easily transferable and can provide a link between a suspect and a victim. For this reason, identifying and comparative analysis of red lipstick - the most popular and used - is required. The aim of this study was to apply a multitechnique methodology for the comparative forensic analysis of the red lipsticks traces of a very similar hue. For this purpose, four methods of different physicochemical basics - two nondestructive spectroscopic and two destructive separation techniques - were used. The possibilities and advantages of attenuated total reflection infrared spectroscopy (ATR-FTIR), confocal Raman microscopy (CRM), capillary electrophoresis (MEKC) and gas chromatography-mass spectrometry (GC-MS) have been combined. Specially prepared lipstick traces in various forms (imprints, smears) on different surfaces (absorbent and nonabsorbent) were analyzed to confirm the usefulness of the proposed methods. The premise is that if two methods yield a consistent result, the investigation is terminated at this stage. All investigated traces were properly identified. First, the ATR-FTIR method as a nondestructive technique is recommended. Sometimes, due to strong interferences from the substrates, the newly proposed method with the use of confocal Raman microscopy may be an alternative. The next recommendation is the MEKC method. Only in case of the absence of unambiguous conclusions, it is proposed to use the GC-MS method. This methodology has the potential to be applied in the comparative analysis of red lipsticks for forensic purposes.