Forensic analysis of automotive paint chips for the identification of the vehicle manufacturer, colour and year of production using electrothermal vaporization coupled to inductively coupled plasma optical emission spectrometry

Abstract

The infrared (IR) diamond cell technology is the main approach used for the identification of vehicles involved in hit-and-run cases. An alternative approach in its infancy is solid sampling electrothermal vaporization (ETV) coupled to inductively coupled plasma optical emission spectrometry (ICPOES) in combination with multivariate statistical tools. Unlike the IR diamond cell approach, ETV-ICPOES does not require the separation of paint layers, bulk analysis of 2 mg paint chips placed in graphite boats being performed after their insertion into the ETV furnace. A temperature program ultimately vaporizes the analytes that are immediately transported into the ICP where they undergo excitation and emit characteristic light. The peak areas of the resulting transient emission signals are then used for the discrimination of samples using linear discriminant analysis (LDA), which requires at least two samples per classification. The approach was applied to samples from different vehicles in two junkyards and resulted in correct matching of 25 samples for manufacturers using Ag, Al, Ca, Cr, Cu, Hg, Mg, Ni, Pb, Pt, S, Sn, Tl, W, and Zr, 26 samples for year of production using Ag, Al, B, Ba, Br, Ca, Ce, Cs, Ge, Hf, Hg, Mg, Si, Te, and Zn, and 31 samples for colour using Au, B, Ba, Ca, Cu, In, Mg, Ni, Pd, Se, V, W, and Zn. The robustness of the approach was demonstrated through correct identification of the manufacturer, year of production and colour of a rusted paint chip.