Forensic Authentication of Paracetamol Using FTIR and UV–Vis Spectroscopy Coupled with Similarity Metrics

Abstract

The global circulation of counterfeit and substandard medicines poses a serious threat to public health and challenges forensic science in generating reliable evidence. Paracetamol, a widely used analgesic and antipyretic, is among the most frequently falsified drugs in low- and middle-income countries. This study employed Ultraviolet-Visible (UV-Vis) and Fourier Transform Infrared (FTIR) spectrophotometry to authenticate paracetamol (PAR). The specific objectives were to examine active pharmaceutical ingredients, and to identify unknown components in paracetamol PAR1– PAR4 samples were analyzed against a certified reference standard. FTIR spectra were obtained using potassium bromide pelletization, while UV–Vis spectra were recorded by dissolving the sample in methanol and phosphate buffer, followed by dilution with distilled water. The data obtained were evaluated by Pearson correlation coefficients (r) and Euclidean distance (ED). Results showed that PAR1 (r ≥ 0.99, ED = 0.051) and PAR3 (r = 0.9983, ED = 0.0389) matched the standard and were classified as authentic. In contrast, PAR2 (r = 0.992, ED = 0.084) exhibited a shifted amide band with reduced absorbance, while PAR4 (r = 0.991, ED = 0.089) showed weakened O–H bands confirming suspect and counterfeit status, respectively. This work addresses a key forensic gap by introducing quantitative, pharmacopeia-compliant thresholds for paracetamol authentication. The novelty lies in combining FTIR and UV–Vis spectra with similarity metrics to deliver objective and legally defensible authentication of paracetamol. The protocol strengthens scientific reliability while offering a scalable, low-cost tool for surveillance and regulatory enforcement in regions most affected by counterfeit medicines.