Stability-Indicating HPTLC Method for Analysis of Venlafaxine Hydrochloride, and Use of the Method to Study Degradation Kinetics

A new quantitative densitometric HPTLC method for stability indicating analysis of venlafaxine hydrochloride, both in bulk and formulations, has been established and validated. Venlafaxine hydrochloride from formulations was separated and identified on silica gel 60F(254) HPTLC plates with butanol-acetic acid water 6:2:2 (v/v), as mobile phase. Densitometry was performed at 254 nm by reflectance scanning; a well-resolved band was obtained at R-F 0.58 +/- 0.02. Response to venlafaxine hydrochloride was a linear function of concentration in the range 100-600 ng, with correlation coefficient, slope, and intercept of 0.9984 +/- 0.0004, 14.54 +/- 0.04, and 141.75 +/- 1.76 respectively. The minimum amounts of venlafaxine hydrochloride that could be authentically detected and quantified were 39.32 and 130.89 ng per band, respectively. The drug does not undergo degradation under oxidative or photolytic conditions but acidic and alkaline conditions resulted in degradation, as was evident from additional peaks observed. When the method was used to investigate the alkaline degradation kinetics it was observed the degradation process followed pseudo-first-order kinetics. The Arrhenius plot was constructed and the activation energy was calculated.