| Summary: | Examining the questioned documents can offer essential scientific proof that the documents are authentic. Examining inks and handwriting to establish authenticity, authorship, suspected counterfeiting, and/or modifications are forensic problems that require critical attention. Due to gel pens popularity and widespread usage, their emergence in criminal cases associated with questioned documents are therefore anticipated. A dissolution test by dissolving gel ink into organic solvent can sometimes be used for rapid discrimination of gel ink into either pigment-based or dye-based colourants. However, due to its extremely destructive nature, this test is unfavourable for forensic document examination purposes. The main aim of this study was to develop a model that could be used to determine the nature of colourant in black gel ink without having to perform the destructive dissolution test. To achieve this, black gel pen inks of different brands/models (n = 30) that were procured from 23 different manufacturers from Malaysia, India, and China were initially dissolved in a series of organic solvents, and the nature of their colourants was recorded. Thereafter, their infrared (IR) spectra profiles were acquired using the attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, and then preprocessed prior to feature selection using the principal component analysis (PCA). The selected features were used for the development of a classifier using the linear discriminant analysis (LDA), whereby 98.1% of correct classification was recorded for the cross-validated samples. Furthermore, it signified the potential of this approach for rapid screening of black gel ink without having to perform the destructive dissolution test, which could be utilised by forensic document examiners. © 2023, Malaysian Society of Analytical Sciences. All rights reserved.
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