Forensic Analysis Of Automobile Paints By Atomic And Molecular Spectroscopic Methods And Statistical Data Analyses

The analysis of 110 automotive paint samples was conducted for the research presented here. Laser-induced breakdown spectroscopy (LIBS) was the central instrument utilized for analysis although scanning electron microscopy / energy dispersive x-ray spectroscopy (SEM/EDS) and Fourier transform infrared spectroscopy - attenuated total reflection (FTIR-ATR) analyses were also performed. Two separate methods of LIBS analysis of samples were used: a cross sectional analysis and a drill down analysis. SEM/EDS analysis focused on the cross section while FTIR-ATR analysis concentrated on the clearcoat layer. Several different data/statistical analyses were evaluated including principal components analysis (PCA), two tailed t-tests based on several different metrics (Hit Quality Index (HQI), Pearson's correlation and Sorenson index), multivariate analysis of variance and receiver operating characteristic (ROC) curves. Full spectrum data analysis from LIBS spectra resulted in 99.7% discrimination between different sample comparisons and 12% between same sample comparisons based on HQI and t-tests. Peak analysis of LIBS spectra resulted in 87.5% discrimination between different sample comparisons and 5% between same sample comparisons based on MANOVA. When combining the results of the FTIR-ATR and SEM/EDS analyses, 88% of the samples could be discriminated.