Abstract
A sensitive, rapid, and eco-friendly spectrofluorimetric method enhanced by nitrogen-doped carbon quantum dots (N-CQDs) was developed for the simultaneous quantification of paracetamol and caffeine in commercial pharmaceutical formulations. Highly fluorescent N-CQDs were synthesized via a one-pot hydrothermal reaction using citric acid and urea as precursor materials. The synthesized nanoparticles exhibited brilliant blue fluorescence under ultraviolet excitation, with a quantum yield of 24.3% and high aqueous stability. The fluorescence intensity of the N-CQDs was selectively modulated by paracetamol and caffeine through distinct non-radiative energy transfer and static quenching mechanisms. Under optimized experimental conditions (pH 7.4 in phosphate buffer, room temperature), linear calibration ranges were established from 0.1 to 25.0 µM for paracetamol and 0.5 to 30.0 µM for caffeine, with limits of detection calculated as 0.032 µM and 0.115 µM, respectively. The proposed method demonstrated excellent selectivity against common pharmaceutical excipients and was successfully applied to commercial combination tablets without requiring preliminary separation steps. Analytical recoveries ranged between 98.4% and 101.6% with relative standard deviations below 2.2%. This CQD-enhanced fluorimetric assay presents a cost-effective, sustainable alternative to high-performance liquid chromatography for routine quality control laboratories.
