Kinetic Spectrophotometric Determination of Isoxsuprine in Dosage Forms Through Derivatisation with 4-Chloro-7- nitrobenzo-2-oxa-1,3-diazole (NBD-Cl)

A simple and sensitive kinetic spectrophotometric method was developed for the determination of isoxsuprine in pharmaceutical preparations. The method is based upon a kinetic investigation of the coupling reaction between isoxsuprine HCl and 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) in borate buffer of pH 7.8 for a fixed time of 30 min. The absorbance of the yellow coloured product was measured at 395 nm. The absorbance- concentration plot was rectilinear over the range of 2-20 μg mL^-1 (r= 0.9994) with minimum detectability of 0.6 μg mL^-1 (1.75 x10^-6M). The different experimental parameters affecting the development and stability of the colour were carefully studied and optimized. The determination of isoxsuprine by the fixed-concentration and rate-constant methods is also feasible with the calibration equations obtained, but the fixed time method has been found to be more applicable. The proposed method was further applied to the determination of the drug in formulations. The results obtained were in good agreement with those obtained using a reference method. The reaction pathway was proposed.