Forensic Characterization of Electrical Tapes Through Layer-Specific Analysis Using ATR-FTIR Spectroscopy and Chemometrics

Abstract

Electrical tapes are frequently used by deviants and criminals to perpetrate violent crimes. These trace materials can be an ideal tool in solving such crimes. Although tapes can consist of multiple layers, their characteristics and primary functions are largely determined by the adhesive and backing layers. In the present study, a total of 25 electrical tapes from different manufacturers were analyzed for both the backing and adhesive sides using a non-invasive, non-destructive analytical technique, ATR-FTIR. The spectral data revealed presence of rubber-based and acrylic-based adhesives with rubber-based adhesives being more common while PVC as the primary backing material. Further chemometric classification using Principal Components (PCs) based Discriminant Analysis (DA) attained an original and cross-validated accuracy of 100% in classification of adhesives and 100% original and 88% cross-validated accuracy in classification of backing. Alternatively, the SVM model demonstrated strong potential as a chemometric classifier, achieving up to 100% accuracy in distinguishing adhesives and backings of electrical tapes, with cross-validation accuracies of 100% for the adhesive side and 92% for the backing side, respectively. Study reveals ATR-FTIR as a valuable analytical tool for preliminary identification of chemical constituents of the electrical tapes and with chemometric models like DA and SVM, it could successfully link adhesives and backings to their respective groups. SVM models which haven’t been used much in previous studies, appeared to perform better than traditional chemometric models in the current study.