Stability Indicating Spectrophotometric Methods for Determination of Vitamin E and Vinpocetine in Their Combined Dosage Form

Abstract

Stability indicating spectrophotometric methods have been developed and validated for determination of Vitamin E (VIT E) and Vinpocetine (VINP) in presence of alkaline induced degradation product of Vinpocetine (DEG) without prior separation. In method (A), two wavelengths were selected for each drug in such a way that the difference in absorbance was zero for the other drugs. Absorbance difference between 217.4 and 234.4 nm were used to determine VIT E while difference between 250.4 and 314.0 nm were selected for VINP determination and the difference between 258.6 and 312.0 nm were selected to determine DEG. In method (B), area under the curve method (AUC) was used for measuring VINP concentration by direct measuring AUC in the range of 330-350 nm, at which no interference from other components. While for determination of VIT E and DEG, the ternary mixture was divided by standard spectrum of 6 μg/mL VINP, in the obtained ratio spectra VIT E and DEG has been directly determined at 210.0 and 230.0 nm, respectively. In method (C), VIT E and DEG were determined by second derivative of ratio spectra (2DD) method by measuring their peak amplitudes at 215.2 and 237.2 nm, respectively, using 6 μg/mL standard spectrum of VINP as a divisor, while the absorbance at isoabsorptive point (λiso=264.4 nm) was used to determine the total concentration of VINP and DEG (where no contribution from VIT E) in the mixture and then by subtraction, VINP concentration could be obtained. The developed methods were validated according to ICH guidelines revealing good accuracy and precision. The results obtained by the proposed methods were statistically compared with those obtained by the reported HPLC methods and no significant difference was obtained. These methods are the first developed SIAM ones for analysis of the studied components.