Spectrofluorimetric Determination of Nepafenac Through Quenching Lanthanide Luminescence in Drug Substance and in Ophthalmic Suspension

Objective: A simple, selective and sensitive spectrofluorometric method is established for the quantitative assay of Nepafenac (NEPA) in pure form and in ophthalmic suspension dosage form. Methods: The fluorescence quenching of Terbium-Tris complex is measured at λ em580 nm after using λ ex 237 nm. The effect of pH, volume of terbium solution and reaction time on fluorescence quenching were studied. The complex formation was found to be highly dependent on the pH. The optimum fluorescence quenching was achieved by using 1.0 ml of (2 × 10-3M) Tb3+ solution and 1.0 ml of Tris buffer solution (pH 10.0). Results: The formed complex was stable for 15 minutes from the starting time of the reaction at room temperature.  The fluorescence quenching of Terbium-Tris complex was linear within the concentration range of 0.25 -10 μg ml-1 with mean percentage recovery of 99.85 ± 0.77 and Correlation Coefficient of 0.9996 (n=5). The sensitivity of the method could be evaluated by limit of detection (LOD) (0.008 µg ml-1) and limit of quantitation (LOQ) (0.024 µg ml-1). Conclusion: Statistical comparison of the results with those of a reported method revealed good agreement.