Use of nitroanilines for spectrophotometric determination of ethinylestradiol in pharmaceutical formulations

Abstract

Three nitroanilines (2-methoxy-4-nitroaniline, 2,4-dinitroaniline and 2-methyl-4-nitroaniline) were tested as spectrophotometric reagents for determination of ethinylestradiol (ETE). The determinations were based on absorbance measurments of the reaction product obtained from the coupling of each diazotized nitroaniline with ETE. Optimization of temperature, pH and diazotization coupling reaction time was realized. 2-Methyl-4-nitroaniline provided the more sensitive system for ETE spectrophotometric determination at 531 nm and the analytical response was linear in the concentration range of 0.65–10.0 µg ml⁻¹. The limit of detection and coefficient of variation were estimated as 197 µg l⁻¹ and 4.5%, respectively. The results showed that the proposed method is simple and rapid, allowing selective determination of analyte. The method successfully determined ETE in oral contraceptive formulations.