Burla Sunitha Venkata Seshamamba - Department of Food Chemistry and Nutrition, College of Food Science and Technology, Bapatla, Andhra Pradesh- ۵۲۲۱۰۱, India.
Peruri Veera Venkata Satyanarayana - Department of Biochemistry, Acharya Nagarjuna University, Guntur, Andhra Pradesh-۵۲۲۵۱۰, India.
Chandra Bala Sekaran - Department of Biotechnology, Jagarlamudi Kuppuswamy Choudary College, Guntur, Andhra Pradesh-۵۲۲۰۰۶, India.

Two simple visible spectrophotometric methods are developed and validated for the quantification of modafinil using 1,2-naphthoquinone-4-sulphonic acid (NQS method) and 2,4-dinitrophenol (DNP method) as analytical reagents. The NQS method involves the reaction of modafinil with 1,2-naphthoquinone-4-sulphonate in alkaline medium at room conditions to form a yellow colored product exhibiting maximum absorption at 430 nm. DNP method is based on the proton transfer from 2,4-dinitrophenol to modafinil at room conditions and then we have theformation of yellow colored ion-pair complex exhibiting maximum absorption at 475 nm. Different variables affecting the reaction were studied and optimized. Under the optimized experimental conditions, Beer's law is obeyed in the concentration ranges of 10-100 and 8-60 μg/mLwith the detection of limit values of 0.486 and 0.258 μg/mL for NQS method and DNP method, respectively The molar absorptivity and Sandell's sensitivity for both of the methods are reported. The methods were validated in terms of accuracy, precision and robustness. The results were satisfactory. The proposed methods were effectively applied to the analysis of the modafinil in their tablet formulations. The recoveries were 99.92% and 99.96% with RSD an 0.863% and 0.722% for NQS and DNS methods, respectively. The assay was not interfered by common excipients.

Narcoleptic drug, naphthoquinone-4-sulphonic acid, dinitrophenol, spectrophotometry, analysis