Effectiveness of UV-Visible Spectroscopy (with Multi-Mode Plate Reader) and ATR-FTIR for the Discrimination of Black Marker Inks: A Chemometric Approach

Abstract

In the ambit of Forensic examination of the questioned documents, writing instruments often serve as an essential tool in disclosing the legitimacy of a document. In the present study, a total of 18 marker samples including 9 permanent and 9 whiteboard (commonly known as dry erase) markers of black color of different brands were purchased from the local market of district Jhansi, Uttar Pradesh, India. UV-Visible spectroscopy with Multi-Mode Plate Reader and ATR-FTIR spectroscopy were used for the discrimination of samples. In the case of permanent marker inks, peaks near 390-405 nm and at 570-585 nm were found to be more prominent and differentiating than that of the whiteboard marker inks. Qualitative comparative analysis of the permanent and the whiteboard black marker ink samples showed 97.2% and 91.6% DP respectively based on their UV-Vis. spectral responses. FTIR spectroscopy of whiteboard markers confirmed the presence of characteristic peak at 1743 cm-1 (C=O stretch) together with a doublet in the region 2920-2850 cm-1 corresponding to asymmetric and symmetric C-H stretch in almost all the whiteboard marker inks, whereas in case of permanent marker inks the former peak 1743 cm-1 was completely absent and the later appeared as a single peak around 2900 cm-1. The results obtained from ATR-FTIR was analyzed using multivariate techniques such as PCA and DFA. PCA was used for the segregation of samples into different groups, whereas DFA was used for the discrimination and classification of marker ink samples. DFA provided a correct classification of 88.9% of the marker ink samples analyzed by FTIR. It is concluded that Multi Mode Plate Reader can be used as a substantial tool for the discrimination of marker inks and was found to be fast and cost effective with high throughput. Moreover, ATR-FTIR results gave some additional information related to the chemical composition of the samples and provided better discrimination when coupled with chemometrics.