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Analysis of 52 automotive coating samples for forensic purposes with Fourier transform infrared spectroscopy (FTIR) and Raman microscopy

ABSTRACT Compounds with Ti, Fe, Cu, Pb, and Cr are often added to coatings as pigments or additives. These heavy metals can be harmful to humans and result in contamination of soils, water, and sediments. Coatings, consisting of complex resins, pigments, and additives, are difficult to analyze. In this study, Fourier transform infrared spectroscopy (FTIR) and Raman microscopy were employed to investigate 52 coating samples with six different colors collected from everyday cases. Infrared has many advantages in identification of resins and additives, while Raman microscopy is more powerful in detecting additives and pigments. It is more effective using these two techniques in combination for identification than using them separately. Cu pigments were detected with high frequencies in blue and green samples; Ti was found in all white samples. Lead chromate pigment has been banned in the United States due to environmental concerns for more than 20 years. However, this pigment is still widely used in many other countries; its main substitute bismuth vanadate is not detected in all samples in this study. The result reveals that environmental scientists should seriously consider the potential ecological and health risks of Pb and Cr from the paints. The analysis of automotive coatings is also important for forensic scientists. Popular pigments, resins, and additives in the coatings are summarized in this study which can provide forensic scientists with helpful references in everyday cases.