Abstract
The dating of ink in questioned documents remains a significant challenge in forensic investigations in Vietnam and other countries. Many forensic examination methods have been usually applied to ensure the highest accuracy of the assessment results while maintaining high environment awareness. In this study, paper characteristics were physically tested to confirm source similarity, and the relative ink dating was established by high-performance thin-layer chromatography (HPTLC). Absolute ink dating by solvent and dye identification was performed by Raman spectrometry—a green technique, using a time-dependent degradation model for crystal violet and the comparison between 2-phenoxyethanol peak intensities. We found that the relative dating of the questioned document was 14 ± 3 months lesser than that of the reference samples, i.e., the absolute age of the questioned samples was estimated to be 24 ± 3 months. The combination of the conventional HPTLC method with the dynamic crystal violet degradation Raman model provides promising results for relative and absolute ink dating of ballpoint pens, which can be applied for documents written 1–15 years prior to the time of examination. The combination of the abovementioned methods demonstrated an acceptable error margin, affording highly practical applications in modern forensic science.
Highlights
Modern document examination often involves investigating the dating of written entries or signatures. is determination relies heavily on ink dating because document falsification usually occurs in the form of the addition or alteration of letters and figures. e importance of ink dating in forensic science began to attract attention only in the late 20th century when an ink reference collection was systematically created for forensic ink dating purposes [1]
The process of dye degradation is the mechanism that is most resistant to environmental factors and occurs over very long periods, as suggested by several studies [4,5,6,7,8]. ese temporal changes can be visualized by using high-performance thin-layer chromatography (HPTLC) methods, which separate dye components and develop them into colored spots on the thin-layer chromatography (TLC) plate
Some studies have reported the use of HPTLC for the differentiation of ballpoint pen inks for forensic purposes in South East Asia and Australia-New Zealand regions [9,10,11], ink dating is still new to this geographical area, and to the best of our knowledge, studies on ink dating using HPTLC results have not been published yet
Summary
Modern document examination often involves investigating the dating of written entries or signatures. is determination relies heavily on ink dating because document falsification usually occurs in the form of the addition or alteration of letters and figures. e importance of ink dating in forensic science began to attract attention only in the late 20th century when an ink reference collection was systematically created for forensic ink dating purposes [1]. Researchers have been investigating these dating methods over the years due to the complex nature of ink, which can include components such as dyes, pigments, solvents, resins, lubricants, biocides, surfactants, corrosion inhibitors, sequestrants, shear-thinning agents, emulsifying agents, pH buffers, and other additives to control the ink characteristics (pH, viscosity, and polymerization) [2]. E estimation of the ink’s age is still a significant challenge to forensic examiners because of the various decomposition mechanisms of the different components after ink is written on paper. E three suggested mechanisms that occur after ink deposition are solvent evaporation, resin solidification, and dye degradation. E rapid evaporation of solvents leads to the drying and diffusion of ink on paper, followed by color alteration due to dye or pigment degradation. Some studies have reported the use of HPTLC for the differentiation of ballpoint pen inks for forensic purposes in South East Asia and Australia-New Zealand regions [9,10,11], ink dating is still new to this geographical area, and to the best of our knowledge, studies on ink dating using HPTLC results have not been published yet
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