Forensic identification of post-chewed smokeless tobacco using ATR-FTIR spectroscopy and chemometrics approaches

Smokeless tobacco (SLT) is an addictive stimulant product used by teenagers and adults in most part of Asia, especially in India by chewing it for a longer time, absorbing nicotine present in it by the tissues, giving a mild stimulation. The availability of different brands of SLT with different composition gives a scope for its differentiation and brand determination. In Indian context, the presence of the spit of post chewed SLT in the floor of a crime scene or in clothing where a close contact with the victim is common. In this work, the proper use of ATR-FTIR coupled with PCA-LDA and PLS-DA were used for the investigation of brand determination from the masticate residue obtained from stimulated crime scenario. ATR-FTIR has an advantage over any other method as it is non-destructive and less time consuming. According to the findings obtained from this study, ATR-FTIR spectroscopy proved to be the best technique for the differentiation of SLT samples. Moreover, the first three principal component of PCA showed 98% variance and LDA exhibited 100% accuracy in predicting the different products of SLT. PLS-DA predicted 100% accuracy in supervised classification of SLT brands with 98% variation from factor 1 and factor 2. The blind validation test was able of predict the unknown samples with their corresponding group without any misclassification.