Chemical characterization of automobile windshield glass samples by nuclear and radio-analytical techniques namely SEM-EDX, ED-XRF, PIXE, PIGE, and INAA and potential of external (in air) PIGE and INAA in conjunction with chemometrics for glass forensics

Abstract

Automobile glass forensics using suitable chemical analysis techniques is an important field in forensic science. In this respect, major elements help to classify the glass samples, whereas trace elements in conjunction with chemometrics are very important to help in grouping for source/origin finding. Five different radioanalytical techniques namely scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDX), energy dispersive X-ray fluorescence (ED-XRF), particle induced gamma-ray/X-ray emission (PIGE/PIXE), and instrumental neutron activation analysis (INAA) were utilized for chemical characterization of automobile (car) windshield glasses and the results have been discussed for possible forensic applications. Methods were validated by analyzing geological and glass-certified/standard reference materials. The R&D work was carried out for 48 real case car windshield glass samples from 10 different manufacturers, whereas the method was standardized for 5 glasses, then applied to 20, and finally to 48 glass samples. From the results of all techniques, it was observed that trace elements like Sc, Cr, Co, Mn, Hf, Ta, Ba La, Ce, Sm, Eu, Yb, and Th obtained by INAA are very helpful for the grouping. Preliminary grouping of the first five samples was carried out utilizing concentration ratios with respect to Sc, La/Ce, and total rare earth elements (REEs) as well as from biplots and ternary plots. External (in air) PIGE and INAA methods were optimized and applied to “as received” glass fragments for confirming the class of glass from major elements and grouping study from trace elements, respectively. Different clustering and grouping methods of chemometrics like cluster analysis (CA) and principal component analysis (PCA) were employed to get the best grouping of similar glasses. PCA using trace elemental concentration was found to be the best approach. Final grouping confirmation of 48 automobile glasses was carried out by PCA, which indicated a clear nine groups from nine branded manufacturers, whereas one set of local glasses did not show any group. The study showed the efficacy of external PIGE and INAA for the classification and grouping study of these soda lime glasses and trace elements in conjunction with PCA for confirmation of grouping needed for forensic applications.