Determination of Ionization Equilibrium Constant of Sildenafil by UV Spectrophotometry / 中国药房

OBJECTIVE:To establish a method for determination of ionization equilibrium constant of sildenafil using ultraviolet spectrophotometry.METHODS:Methanol solutions of sildenafil with pH values of 2.26,8.56,9.31,9.83 and 12.38 were respectively scanned at the wavelength within the range of 200nm～400nm.The absorbability and pKa value of sildenafil were determined at the selected wavelength of 280,287,290,295 and 297nm respectively.RESULTS:The pKa value of sildenafil was 9.35?0.02.CONCLUSION:The present method is convenient and practicable.