Abstract
In this study, two very promising techniques, micro X-ray fluorescence (μXRF) and laser-induced breakdown spectroscopy (LIBS) were applied to the examination of Polish banknotes – Polish zloty (zl).Several areas on each banknote were selected and analysed. Different elemental compositions were identified after comparing the spectra recorded from various measurement locations. It was possible to identify characteristic atomic emissions from one or several elements such as Ca, Ti, Fe, Ba, Co, Cr, Cu, Mg, Mn, Ni, V, and Zr, depending on the banknote denomination, issue date, and evaluated spot. Potentially good discriminators with unique elemental composition were identified: black serial number (C) and microlettering (A). A comparison of brand-new banknotes with used banknotes (which have been in circulation) was also performed. The middle horizontal section of the banknotes shows higher exposure to contamination and consequently constitutes the most difficult part to analyse. Counterfeit banknotes were also analysed and were clearly distinguished from authentic notes in all cases. It was demonstrated that a comparison of the elemental composition is a useful way to detect counterfeit banknotes (10, 20, 50 and 100 zl) in ‘real-world’ cases.This study shows the potential of LIBS and μXRF as effective and practical techniques to analyse Polish banknotes. Their many advantages provide a good alternative to the analytical methods routinely used for the examination of these objects.
Highlights
Forgery of banknotes is a major financial crime
This study shows the potential of laser-induced breakdown spectroscopy (LIBS) and μXRF as effective and practical techniques to analyse Polish banknotes
The results differed from those originating from μXRF analysis and showed technological dissimilarities in old issue (OI) and new issue (NI) banknotes manifesting in different elemental compositions of the same measuring areas (e.g. Ba in area A)
Summary
Forgery of banknotes is a major financial crime. This illegal practice, which is developing both qualitatively and quantitatively, constitutes an important problem for governments around the world. The potential of portable X-ray fluorescence (pXRF) spectrometry [12] and portable near-infrared spectroscopy (pNIR) [13] was shown in the examination of differently coloured regions of dollar, euro, and real banknotes These methods were supported by chemometric methods, including principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA). Previous literature [23,24,25,49,50,51,52,53] shows the potential of LIBS for the examination of colouring matter on paper using this technique It was selected for the present study in order to choose the most discriminating areas on Polish banknotes based on elemental analysis. To the best of the authors' knowledge, this is the first publication that correlates results from LIBS and μXRF for forensic banknote examinations
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