Discrimination of White Automotive Basecoat Paint Fragments Using Synchrotron Radiation X-ray Fluorescence Spectrometry

This study has demonstrated that synchrotron radiation X-ray fluorescence spectrometry (SR-XRF) is a highly effective technique for the forensic discrimination of white automotive basecoat paint fragments. Eighteen samples of white automotive solid paints were collected, and fragments of the white basecoat layers were used as analytical samples. Fourier transform infrared (FT-IR) microspectroscopy and SR-XRF were conducted for material and trace elemental analyses, respectively. The samples could be divided into five groups based on any differences of the materials by FT-IR microspectroscopy. Elements like Ti, Cr, Fe, Cu, Zn, Pb, Br, Sr, Zr and Nb were nondestructively detected in small fragments. The samples could be divided into two groups based on the presence or absence of Nb. The other trace elements that were detected could be used as indicators to further discriminate the samples. Normalized X-ray intensities, which were the intensities of Ti normalized by those of Nb, were used to compare samples that were indistinguishable based on the observed composition of trace elements. The normalized X-ray intensities of Ti/Nb could be measured with a precision of less than 5.0 %, and were found to be effective parameters for identifying white basecoat fragments. Through the combined use of FT-IR microspectroscopy and SR-XRF, 152 out of 153 pairs among 18 samples (C-18(2)) could be properly discriminated.