Application of Bivariate Calibration Method and Derivative Spectrophotometry to Simultaneous Quantitative Resolution of Ethinylestradiol and Levonorgestrel in Pharmaceutical Formulations

The bivariate calibration method was applied to the quantitative resolution of ethinylestradiol (ETE) and levonorgestrel (LEV) in pharmaceutical formulations and the results were compared with those given by first derivative spectrophotometry. In the bivariate spectrophotometric method, an optimum pair of wavelengths was chosen for the determination. The determination was performed at 240.4 nm for ETE and at 257.8 nm for LEV. In the first-derivative spectrophotometry determination of ETE and LEV was realized by measurements of amplitudes of derivative spectra corresponding to zero-crossing points of LEV and ETE at 241 and 248.4 nm, respectively. The proposed procedures were validated by using various synthetic mixtures with high percentage of recovery and good precision. Mean recovery values were found 103.4 % and 102.9 % for bivariate calibration method and 102.4 % and 98.2 % for derivative spectrophotometry, respectively, for determination of ETE and LEV in synthetic mixtures. Also good agreement between the results obtained using the two procedures was found, which agreed also with the product label