Application of ATR-FTIR spectroscopy and chemometrics to the forensic examination of duct tapes

In cases involving kidnappings, homicides, sexual assaults, and improvised explosive devices, duct tapes are frequently subjected to forensic analysis as physical evidence. The analysis of such evidence can provide an evidentiary link between the suspect, the victim, object, and/or the crime scene. In the present study, 15 brands of duct tapes have been analyzed using ATR-FTIR (attenuated total reflectance Fourier transform infrared) spectroscopy. Three components of duct tape were analyzed, namely, the adhesive, backing and fabric rein-forcement. Samples (1 cm2) were analyzed from the region 4000-600 cm-1. Chemometric methods-PCA (prin-cipal component analysis) and PCA-LDA (linear discriminant analysis) were used to interpret the data and classify the samples into their respective classes. Sample clustering due to similar chemical composition was visualized using PCA. PCA-LDA yielded an accuracy of 96.67 % for the adhesive, 71.67 % for the backing, 66.07 % for warp yarn and 69.64 % for fill yarn. The use of results from the analysis of the all three components enabled discrimination between all the samples. The validation results showed an accuracy of 93.37 %, 70 %, 64.28 % and 67.85 %% for adhesive, backing warp yarn and fill yarn respectively. Preliminary investigation on the effect of substrates (cardboard, plastic and skin) on the discrimination of duct tapes yielded the following PCA-LDA accuracy: 60 % for the adhesive, 73.34 % for the backing, 60 % for warp yarn and 66.67 % for fill yarn. The use of chemometrics for the discrimination has enabled to maximise the information obtained from the duct tapes in a more objective manner.