Differentiation and evaluation of evidence value of styrene acrylic urethane topcoat car paints analysed by pyrolysis-gas chromatography

Pyrolysis (Py)-GC/MS was applied to differentiate between automobile paint samples. The method was used for analysis of 36 samples of styrene acrylic urethane clearcoats that were indistinguishable on the basis of their infrared spectra and elemental composition. Differences observed in the obtained pyrograms of the compared paint samples were relatively small. Therefore, statistical analysis of the obtained results was performed. The likelihood ratio test suitable for multivariate data analysis supported by analysis of data structure by graphical model was used. This approach allowed not only distinguishing the samples compared, but also allowed the evaluation of the evidential value of such observations, which is very important from a forensic point of view.