A Highly Selective and Sensitive Spectrofluorimetric Method for the Determination of N-acetyl-4-aminophenol at Nano-trace Levels in Pharmaceuticals and Biological Fluids Using Cerium (IV)

A very simple, rapid, ultra-sensitive, highly selective and non-extractive spectrofluorimetric method for the determination of N-acetyl-4-aminophenol (paracetamol) at ultra-trace levels has been developed. This method was based on the oxidation of paracetamol in presence of slightly acidic (0.05 - 0.15 M H2SO4) aqueous solution with a prompt oxidizing agent, cerium(IV) for the direct spectrofluorimetric determination of paracetamol and the fluorescent species is an oxidation product of parcetamol, has excitation and emission wavelength at λex = 255 nm and λem = 350 nm, respectively. The fluorescence intensity of oxidation product reaches a constant value (after heating for 5 min at 45 ± 5°C) within 15 min remains stable for over 24 h. Numerous variables influencing the reaction’s conditions e.g. the concentrations of cerium(IV), temperature, effect of acidity, time of the reaction and solvents were cautiously experimented and optimized. Linear calibration graphs were obtained for 10-700 µgL-1 of paracetamol, having a detection limit of 2 µgL-1; the quantification limit of the reaction system was found to be 10 µgL-1; the RSD was 0-2% and the correlation coefficient, R2 = 0.9999. A large excess of over 40 potentially interfering excipients, commonly present in dosage forms were tested in the determination of paracetamol at 100 µgL-1 level, do not intervene in the determination process. The developed method was successfully applied to the determination of paracetamol in commercial pharmaceutical formulations and biological fluids. The results of the proposed method for pharmaceuticals and biological analyses were analogous with that of spectrophotometric method and the Official method stated in the British Pharmacopoeia, and was found to be in an excellent agreement.