Stability indicating LC method for the estimation of venlafaxine in pharmaceutical formulations

A rapid, selective and stability indicating high performance liquid chromatographic method was developed and validated for the estimation of venlafaxine in pharmaceutical dosage forms. The analysis was done on a Spherisorb C8 (4.6 x 250 mm, 5 microm) column. The mobile phase consisted of acetonitrile:sodium dihydrogen orthophosphate [0.04 M], pH 6.8 (75:25) at a flow rate of 1.5 ml/min. Detection was carried out at a wavelength of 224 nm. The developed method was found to give good separation between the pure drug and the degraded product. The polynomial regression data for the calibration plots showed good linear relationship in the concentration range of 1-10 microg/ml with r=0.9999. The method was validated for precision, accuracy, ruggedness and recovery. The minimum detectable and minimum quantifiable amounts were found to be 150 and 600 ng/ml, respectively. The drug was stable under basic and oxidative conditions. However, the sample treated with acid showed an additional peak at a retention time of 4.32 min other than the main peak at a retention time of 5.32 min. Statistical analysis proves that the method is reproducible and selective for the estimation of venlafaxine. As the method could effectively separate the drug from the degradation product, it can be employed as a stability indicating one.