Discrimination of nail polish using attenuated total reflectance infrared spectroscopy and chemometrics

Trace nail polish evidence recovered in forensic investigations can serve as important corroborative evidence and assist in crime reconstruction, especially in cases related to physical and sexual assault against women. Nevertheless, nail polish evidence has been neglected either owing to its infrequent occurrence or, when it is encountered, it is present in only a trace quantity, which makes the analysis difficult when using conventional techniques. In this study, ATR-FTIR spectroscopy has been employed for the analysis of 19 brands of nail polish with 73 different series (similar shades). The spectra obtained using this technique have been interpreted statistically using PCA and Correlation Coefficient methods with discriminating powers of 99.5% and 99.3% respectively. The spectrum of nail polish showed various functional groups: aliphatic amine, aliphatic and aromatic nitro groups of nitrocellulose, alcohol, acid, and aromatic ester. In addition, peaks of alkyne groups indicative of talc or mica compounds were also observed. The current research methodology effectively differentiated almost all the samples and has the prospect of potential application in future forensic casework.