Characterization and profiling of security inks and materials in international banknotes using ATR-FTIR spectroscopy coupled with chemometrics

Purpose This study aims to characterize key components of banknotes such as security inks, substrate paper and security threads from 12 different countries using spectroscopic and chemometric approaches. Design/methodology/approach Banknotes belonging to the countries India, China, Bangladesh, Russia, the UK, EU, the USA, Australia, Indonesia, South Africa and the UAE have been examined. Attenuated total reflectance-Fourier transform infrared spectroscopy, in conjunction with multivariate chemometric techniques, was used to evaluate chemical composition, identify patterns of similarity and discriminate between different banknotes. Findings Spectral profiling revealed the presence of materials such as cellulose, calcium carbonate, kaolinite, dialdehyde starch and oxime-based compounds. Two main types of security threads were identified: demetallized threads exhibiting high signal-to-noise ratios and acrylic polymer-based plastic threads. Among all regions analyzed, the intaglio ink and substrate paper areas were selected for statistical analysis. Principal component analysis accounted for 97% of variance across the complete data set, and 99% and 97% variance in paper and intaglio ink groups, respectively. Classification using principal component analysis-linear discriminant analysis achieved 91.67% accuracy overall, which improved to 100% when ink and paper were analyzed independently. Partial least squares discriminant analysis further enhanced classification, yielding 97% accuracy. A blind validation study confirmed the robustness of the models, predicting unknown samples with 100% accuracy. Originality/value The study presents a novel comparative approach to the spectroscopic profiling of banknote materials, addressing a significant gap in the forensic and analytical characterization of global currencies. By providing comprehensive spectral information and demonstrating successful classification, the work offers valuable insights into the chemical consistency and sourcing of banknote raw materials.