title: Determination of ethinyloestradiol in the presence of norethisterone by derivative-difference spectrophotometry.
abstract: A simple and direct method for the determination of ethinyloestradiol as a minor component in the presence of norethisterone and in oral contraceptive tablets is presented. The method is based on measuring the signal intensity, d delta A/d lambda and d2 delta A/d lambda 2, of the generated first and second derivative spectra of the delta-absorbance curves obtained by measuring solutions in methanol and methanol-sodium hydroxide at certain wavelengths. The method has been applied to the determination of ethinyloestradiol in oral contraceptive tablets, with a coefficient of variation of less than 2%.
mesh_terms: D004997:Ethinyl Estradiol / Q000032:analysis*; D009640:Norethindrone / Q000032:analysis*; D013056:Spectrophotometry, Ultraviolet; D013607:Tablets
chemical_list: D013607:Tablets; D004997:Ethinyl Estradiol; D009640:Norethindrone