Utilização de técnicas analíticas instrumentais voltadas para a datação de tinta de caneta na química forense

Abstract

Forensic chemistry connects science with justice, applying scientific techniques and methodologies that help in finding information and elucidation of crimes committed by identifying different types of chemical compounds, thus facilitating criminal investigations. Among the different areas that make up forensic chemistry, documentoscopy is of great importance. It is responsible for providing historical information of a document, evaluating its veracity for legal purposes, such as in an attempt to date writings with a pen. In our study, simulations were carried out in an aging laboratory for blue ballpoint pen inks, focusing mainly on the Crystal Violet (Basic Violet 3) compound, which is the main chemical constituent of pens. The inks were subjected to a camera with the direct incidence of lamps with emission in the ultraviolet and visible regions, at different exposure times and the analyses were performed by infrared (IR) spectroscopy by Fourier transform with attenuated total reflection mode to assess the degradation of the chemical composition of inks. The IR spectra showed regions with peaks that suggested some interesting changes in the chemical composition after the artificial aging process, for the peaks in 752, 1244, and 1584 cm-1. Thus, the proposal was also used in an attempt to date pen ink for real documents containing writings dated between the years from 1975 to 2017. The data showed similarity with the results found in the simulated aging experiments, where it was possible to notice main-ly that there was a reduction in the absorption band referring to the 1584 cm-1 peak, due to chemical modification related to the C=N bond in the Basic Violet 3 molecule. Furthermore, a divergence between the IR spectra between the artificially aged samples and the real ones, for the peak at 752 cm-1, suggests that there may be more than one degradation mechanism in the paint aging process. Thus, the proposed method demonstrates the potential for performing routine analyses in the field of documentoscopy, for pen ink dating.