Development and Validation of a Stability-Indicating Assay Method for Naftopidil

A sensitive, selective, precise, and stability-indicating high-performance thin-layer chromatography (HPTLC) method for the analysis of naftopidil both as bulk drug and its formulations were developed and validated. The method employed TLC aluminum plates precoated with silica gel 60 F-254 as the stationary phase. The solvent system consisted of toluene-ethyl acetate-methanol-triethylamine (8:2:0.5:0.3, v/v). Densitometric analysis of naftopidil was carried out in the reflectance-absorbance mode at 254 nm. This system was found to give compact spots for naftopidil (R-F value of 0.52 +/- 0.02, for six replicates). Naftopidil was subjected to acid and alkali hydrolysis, oxidation, dry and wet heat treatment, and photodegradation. The drug undergoes degradation under acidic and basic conditions, oxidation, and photodegradation. Also, the degraded products were well resolved from the pure drug with significantly different R-F values. The method was validated for linearity, precision, robustness, limit of detection (LOD), limit of quantitation (LOQ), specificity, and accuracy. Linearity was found to be in the range of 500-2500 ng spot(-1) with significantly high value of correlation coefficient r(2) = 0.997. The LOD and LOQ were 95.17 and 267.89 ng spot(-1), respectively. As the method could effectively separate the drug from its degradation products, it can be employed as a stability-indicating one.