Stability Indicating HPTLC Method for Analysis of Rifaximin in Pharmaceutical Formulations and an Application to Acidic Degradation Kinetic Study

A specific stability indicating high-performance thin-layer chromatographic method for analysis of rifaximin both as a bulk drug and in formulations was developed and validated. The method employed HPTLC aluminium plates precoated with silica gel 60 F254 as the stationary phase. The optimized mobile phase system consisted of n-hexane : 2-propanol : acetone : ammonia (5 : 4.1 : 1, v/v/v/v), which gave compact spots for rifaximin at of 0.59 ± 0.03. Rifaximin was subjected to forced degradation studies in order to check the specificity of the method. Densitometric analysis of rifaximin was carried out in the absorbance reflectance mode at 443 nm. The calibration plots showed linear relationship in the concentration range of 400–3200 ng per band. Moreover, linearity was also confirmed by verification of homoscedasticity of variance. According to validation studies, the developed method was repeatable and specific as revealed by % RSD less than 2 and hence can be used for routine analysis of pharmaceutical formulation. Moreover, the method could effectively separate the drug from its degradation products; hence it can be employed as a stability indicating one. The kinetics of acid degradation process at various temperatures was also investigated and first-order rate constant, half-life, shelf life, and activation energy were computed.