Characterization of Brazilian banknotes using portable X-ray fluorescence and Raman spectroscopy

As technology advances, counterfeiters improve their techniques reproducing banknotes with more accuracy. Spectroscopic techniques may be applied for characterization of these forgeries. The aim of this study was to develop a methodology for banknotes characterization employing portable X-ray fluorescence (pXRF) and portable Raman spectroscopy (RS) equipment for measurements in genuine and counterfeit Real (Brazilian currency) banknotes. Quantification of the metals in the ink and paper was carried out with pXRF data, using a sensitivity curve. pXRF spectral analysis was effective to discriminate between genuine and counterfeit bills. Moreover, the quantification of the metals enriched the analysis, since it was possible to compare elements concentration that are commonly found in genuine and counterfeit banknotes. The use of partial least square discriminant analysis (PLS-DA) applied to pXRF data was efficacious to identify fake banknotes and it may be used for further investigation about the provenance of forgeries. Principal component analysis (PCA) grouped forgeries from different seizures based on similarities in the elemental composition. The spectra obtained by RS allowed identification of characteristic bands of two pigments from the inks: phthalocyanine and diarylide. For the RS data, PLS-DA and PCA successfully discriminated R$ 50 genuine and fake banknotes.