Rapid forensic characterization of automotive clear coats by ATR-FTIR combined with chemometrics

Abstract

Hit-and-run criminal behavior is a challenge for law enforcement agencies around the world. Paint chips left at a crime scene become important for the criminal investigation process. The clear coat is of great interest since it is most likely to be transferred through contact and therefore found at the crime scene. Fourier transform infrared spectroscopy with attenuated total reflectance (ATR-FTIR) spectroscopy combined with chemometric tools is shown to efficient for forensic examination of clear coats. The possibility of improving the chemometric model generalizability was shown through a dataset encompassing diverse 125 samples. The chemical signatures of melamine cross‐linking and urethane were observed during investigation of spectral data of individual clear coats. The best exploratory principal components analysis (PCA) model was constructed with the first four principal components (PCs), that described 90.3 % of the total data variance. Supervised model classification using partial least squares – discriminant analysis (PLS-DA) showed ssensitivity (SEN) and specificity (SPC) of 95 % and 100 % for external test set (overall accuracy was 92 %). Independent components analysis (ICA) model with 6 independent components (ICs) was used to interpret chemical features responsible for class separation. High predictive ability and interpretability of multivariate approach demonstrates the potential of ATR-FTIR spectroscopy and chemometrics for characterization of automotive clear coats of various manufacturers and models.