Forensic Study on Chemical Stability of Indian Banknotes Using ATR-FTIR Spectroscopy

Abstract

Background: Currency notes serve as the primary medium of financial transactions in India and are subjected to continuous
handling and exposure to environmental factors such as moisture, heat, dust, oils, and other contaminants during circulation.
These conditions may contribute to gradual chemical and physical alterations in the paper substrate of banknotes. Furthermore,
the demonetization initiative implemented in 2016 resulted in the withdrawal and replacement of several denominations,
significantly affecting circulation patterns, handling frequency, and the lifespan of Indian banknotes. Evaluating the chemical
stability of circulated banknotes is therefore important from both forensic and material science perspectives.
Objective: This study aimed to investigate the occurrence of chemical degradation and compositional changes in Indian
banknotes using Attenuated Total Reflectance–Fourier Transform Infrared (ATR-FTIR) spectroscopy.
Materials and Methods: A total of 32 Indian banknotes comprising 25 circulated and 7 fresh notes from five denominations (₹10,
₹50, ₹100, ₹200, and ₹500) were analysed. Five distinct regions of each banknote were selected to assess localised chemical
changes resulting from circulation and environmental exposure. ATR-FTIR spectra were recorded in the mid-infrared region
(4000–400 cm⁻¹). Characteristic absorption bands corresponding to O–H stretching (~3330 cm⁻¹), aliphatic C–H stretching
(~2900 cm⁻¹), and cellulose fingerprint vibrations (~1427 cm⁻¹) were normalised against the glycosidic C–O/C–O–C band
(~1050 cm⁻¹). Statistical evaluation was performed using the non-parametric Mann–Whitney U test in Microsoft Excel 2019.
Results: No statistically significant differences were observed in the normalised O–H and C–H ratios between fresh and
circulated notes (p > 0.05). However, the cellulose fingerprint ratio (A1427/A1050) exhibited a moderate trend toward variation
in circulated banknotes (p = 0.092). Region-wise analysis revealed localised significant differences in specific areas, likely due
to surface contamination and moisture interaction rather than extensive chemical degradation.
Conclusion: The results showed the cellulose fingerprint ratio emerged as the most sensitive indicator of circulation-related
changes, reflecting subtle cellulose degradation associated with frequent handling and use.