Accurate quantitation of low dose, multi-active dissolution samples poses unique challenges in the pharmaceutical industry, often resulting in separate HPLC methods for each active or the use of multiple detectors for increased sensitivity. In this study, we report a fast, isocratic HPLC method utilizing only UV detection for dissolution testing of low dose desogestrel and ethinylestradiol tablets. Rapid separation is completed in 5 min using isocratic elution at a flow rate of 0.45 mL/min, with a column temperature at 30 °C, an injection volume of 50 μL and the detection wavelength at 200 nm. After extensive method development and optimization, the cyano stationary phase was used to overcome the large difference in hydrophobicity for desogestrel and ethinylestradiol, providing balanced retention for both analytes under isocratic elution. Chromatography modeling software was used to provide a rapid analysis of multiple columns and chromatography conditions. The optimized method boasts fast and efficient separation through use of a short, small I.D. column and a large injection volume of dissolution solution to achieve high sensitivity. The stable baseline from an isocratic separation allows low detection wavelengths to be used, resulting in accurate and precise quantitation of both desogestrel and ethinylestradiol. The method has been successfully validated for specificity, linearity, accuracy and precision in the range of 75 - 600 ng/mL for desogestrel and 10 - 80 ng/mL for ethinylestradiol using both HPLC and UHPLC systems. The method robustness was characterized using a design of experiment approach, and the operational design region of the method was established.
Keywords: Cyano stationary phase; Desogestrel; Dissolution; Ethinylestradiol; HPLC.
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