Microespectroscopia no infravermelho médio por transformada de Fourier no modo reflexão total atenuada e técnicas quimiométricas aplicadas à detecção de fraudes em documentos

Abstract

Crossing lines, ink dating and chemical erasure are some of the major problems that confront analysis of questioned documents. Conventional magnification techniques do not provide conclusive results for samples of overlapping lines, since darker colors cause the optical illusion that they are on top of the clearest, which is the case or not. The InfraredSpectroscopy is ideal for forensic analysis of inks on documents because it combines the chemical selectivity with the fact of being a non-destructive technique that requires no sample preparation. Multivariate and highly correlated nature of spectroscopic data requires to be processed by chemometric tools, which allow the extraction of the maximum amount of information of these multicomponent systems. In this context, it was aimed to determine the chronological sequence of strokes in heterogeneous intersection regions, discriminate and dateinks involved in homogeneous intersections, and detect chemical erasure by Micro-Attenuated Total Reflection Fourier Transform Infrared Spectroscopy and Partial Least Squares for Discriminant Analysis.The proposed method showed to be adequate both in cases of heterogeneous line crossing (involving printing and ink pen) in which was used laser printing and when were present lines traced by inkjet printer. Furthermore, the method was able to differentiate the strokes of five among the six analyzed samples of homogeneous line intersection. In the dating stage, the accelerated aging exposure time was not sufficient to cause degradation of colorants inks detectable by the technique. Regarding the detection of chemical erasure, the results obtained by ultraviolet radiation corroborated those obtained by ATR-FTIR and PLSDA.