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The purpose of current study is to estimation the orlistat in pure form and pharmaceutical formulations by a simple, exact, precision, accurate and sensitive spectrophotometric technique via the use of the organic reagent NQS (1,2-Naphthoquinone-4-sulfonic acid sodium salt) In an alkaline medium. The maximum absorption of pure drug (Orlistat) was recorded at the wavelength (λmax) 212nm and the wavelength of the reagent NQS at 365nm. The wavelength of the products was 469 nm. The optimum conditions for this reaction were studied, where included the best reagent concentration (NQS), the optimum volume of the reagent, Acidity function has an effective role in increasing the absorbance the of color product, best time for the stability of the colored, and the effect of different temperature was also studied.
The ideal addition of drug, reagent and base solution recorded an increase in absorbance, as the order of addition was( Drug +NQS + NaOH ). After completing the study of the optimal conditions and obtaining the best results, a calibration curve was built for orlistat, which was found to comply the Beer-Lambert's law obeyed with range of concentrations (20 - 400) µg. mL-1and the Linearity correlation was 0.9992 and the value of the molar absorptive constant was 1735.06 L.mol-1.cm-1 and Sandal’s sensitivity is 0.0122 µg.cm-² and its stability constant was 5.43×105. This study showed that the effect of some additives in the pharmaceutical compounds had no effect on the product reaction. Determination of Orlistat in the pharmaceutical formulation and some body fluid by NQS reagent was very successfully.