Use of Brominating Agent for the Spectrophotometric Determination of the Narcoleptic Drug Modafinil

Two simple and sensitive visible spectrophotometric methods (I and II) are developed for the quantification of modafinil in pure and in tablet formulations. The methods (I and II) are based on the bromination of modafinil by a bromate/bromide mixture of known concentration in acid medium. The determination of residual bromine is based on its ability to bleach methyl orange (method I) and methylene blue (method II) and measuring the absorbance at 525 nm and 664 nm, respectively. In both methods, the amount of bromine reacted with the dye corresponds to the drug content. The different experimental parameters affecting the reaction and stability of the colored product are carefully studied and optimized. Beer s law is obeyed in the concentration ranges of 0.5-5.0 and 0.75-4.5 μg mL^-1 with regression coefficient of 0.9981 and 0.9995 for methods I and II, respectively. The limits of quantification (LOQ) were 0.0540 and 0.0536 μg mL^-1 for methods I and II, respectively. After validation according to the guidelines of International Conference on Harmonization, the proposed methods were successfully applied to assay modafinil in its tablet formulations. The label claim percentages were 99.97 ± 0.896% and 99.98 ± 0.884% for the methods I and II, respectively. No interference was observed from common excipients found in pharmaceutical preparations.