On the criteria for the discrimination of inkjet printer inks using micro‐Raman spectroscopy

Inkjet printers are ubiquitous devices in our society. Therefore, it is not surprising that they are used to commit different types of illicit activities such as threats or extortions by means of anonymous letters, frauds in the context of disputed contracts, alterations to or counterfeit of ID documents, or counterfeit of currency banknotes. This latter application is of primary interest in this study, where a method to rapidly develop investigative leads is required. Inkjet printed documents produce microscopic colored dots that can be detected using a microscopical approach in conjunction with Raman spectroscopy. The overall goal of this project is to investigate if Raman data gathered from the three cyan, magenta, and yellow microscopic colored dots constitute, in conjunction, a chemical signature of sufficient discriminating quality to provide reliable investigative leads in a time‐effective and nondestructive manner. In the present phase of this study, the criteria necessary to achieve discriminations between inkjet printer inks from different manufacturers, the same manufacturers, and even the same models have been evaluated on a set of 11 samples. Although Raman spectroscopy is already a relatively well‐established method for the characterization of colorants (both dyes and pigments), this study demonstrates that the contribution of minor peaks within Raman spectra improves the discriminating capabilities of the technique. The joint consideration of the three colored components was also effective in differentiating inkjet printer ink samples, especially those from the same manufacturer and in some instances from the same model as well. Micro‐Raman spectroscopy is applied to differentiate cyan, magenta, and yellow microscopic colored dots from inkjet printed documents in a forensic context. This study shows that the detection of minor peaks within Raman spectra improves the discriminating capabilities of the technique. The simultaneous consideration of the three targeted colored components resulted in effective differentiation of inkjet printer ink samples, especially those from the same manufacturer and, in some instances, from the same model.