Analysis of automotive paints by ATR FT-IR microspectroscopy

Abstract

ATR FT-IR microspectroscopy is used to analyze and identify the automotive paints. Three types of automotive paints including paint chips of different colors and shades, multilayer automotive paints, and thin trace smear on automotive paint were characterized by ATR FT-IR microspectroscopy. Two homemade [micro]ATR accessories; the slide-on diamond [micro]IRE and the slide-on Ge [micro]IRE, using an infrared microscope were employed for surface characterization of automotive paints. The spectra acquired by the slide-on diamond [micro]IRE and the slide-on Ge [micro]IRE were similar to those acquired by conventional ATR technique. The spectra from different colors and shades of paint show different spectral features due to the difference in compositions such as binder, pigment, and additive. Due to small contact area of the slide-on diamond [micro]IRE and slide-on Ge [micro]IRE, an individual layer of the multilayered automotive paints can be selectively analyzed without layer separation changing in chemical composition in each small sampling position can be analyzed. In additional, paints with the same colors but different chemical composition can be identified by surface line mapping. Thin trace smear were analyzed directly without interference from paint support by the slide-on Ge [micro]IRE. The slide-on diamond [micro]IRE and the slide-on Ge [micro]IRE were suitable for forensic analysis of automotive paint because of their small contact area and good contact with the sample. The technique is non-destructive, has short analysis time, can be performed without a sample preparation.