Abstract
For the forensic analysis of multi-layered paint chips of hit-and-run cars, detailed compositional analysis, including minor/trace chemical components in the multi-layered paint chips, is crucial for the potential credentials of the run-away car as the number of layers, painting process, and used paints are quite specific to the types of cars, color of cars, and their surface protection depending on the car manufacturer and the year of manufacture, and yet overall characteristics of some paints used by car manufacturers might be quite similar. In the present study, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) imaging, Raman microspectrometry (RMS), and scanning electron microscopy/energy-dispersive X-ray spectrometric (SEM/EDX) techniques were performed in combination for the detailed characterization of three car paint chip samples, which provided complementary and comprehensive information on the multi-layered paint chips. That is, optical microscopy, SEM, and ATR-FTIR imaging techniques provided information on the number of layers, physical heterogeneity of the layers, and layer thicknesses; EDX on the elemental chemical profiles and compositions; ATR-FTIR imaging on the molecular species of polymer resins, such as alkyd, alkyd-melamine, acrylic, epoxy, and butadiene resins, and some inorganics; and RMS on the molecular species of inorganic pigments (TiO2, ZnO, Fe3O4), mineral fillers (kaolinite, talc, pyrophyllite), and inorganic fillers (BaSO4, Al2(SO4)3, Zn3(PO4)2, CaCO3). This study demonstrates that the new multi-modal approach has powerful potential to elucidate chemical and physical characteristics of multi-layered car paint chips, which could be useful for determining the potential credentials of run-away cars.
Highlights
When a car traffic accident occurs, pieces of paint chips from the surface coating of the cars can be scraped out and remain on the spot, even when the car runs away from the site
For chemical analysis of coating and paint samples of automobiles, various techniques, such as laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) [3], laser-induced breakdown spectroscopy (LIBS) [4], pyrolysis gas chromatography-mass spectrometry (GC-MS) [5], and time-of-flight secondary ion mass spectrometry (TOF-SIMS) [6], have been employed as destructive analytical tools, while micro X-ray fluorescence [7,8], scanning electron microscopy/energy-dispersive X-ray spectrometry (SEM/EDX) [9], Raman microspectrometry (RMS) [10], Fourier transform infrared spectroscopy (FTIR) [11], synchrotron FTIR [12], and attenuated total reflectance FTIR (ATR-FTIR) in conjunction with multivariate chemometrics [13] have been reported to be more promising for forensic purposes due to their non-destructive or semi-destructive nature
ATR-FTIR imaging, RMS, and SEM/EDX were applied in combination for a detailed characterization of three samples of car paint chips
Summary
When a car traffic accident occurs, pieces of paint chips from the surface coating of the cars can be scraped out and remain on the spot, even when the car runs away from the site. SEM/EDX can provide information on the physical structures and elemental compositions of micrometer-sized samples with submicron lateral resolution, and yet it has limited capabilities for performing molecular speciation of particles. Vibrational spectroscopic techniques, such as RMS and ATR-FTIR, are powerful for functional group analysis and molecular speciation of organic and inorganic chemical compounds, including hydrated species, under ambient conditions. Molecular ATR-FTIR species of imaging organic polymer resins and inorganic were using this multi-modal and Raman spectral data can compounds, and on on their distributions onorganic a micrometer. To investigate the chemical and physical characteristics of car paintinvolved chips inin detail, which would be powerful for elucidating the potential credentials of cars involved in hit-and-run accidents
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