Spectrophotometric Determination of Drugs Using 2,3-Dichloro 5,6-dicyano p- benzoquinone as Analytical Reagent

Six drugs viz., Astemizole, Domperidone, Esomeprazole, Losartan potassium, Sumatriptan and Terazosin were tested for the formation of charge transfer complexes with 2, 3-dichloro 5, 6-dicyanopbenzoquinone, (DDQ). Each of these drugs turned the pale yellow colour of reagent i.e DDQ. in CH3CN, to purple and exhibited three bands at 455, 545 and 588 nm due to anion of the reagent whose intensity increased with increase in the concentration of the drugs and formed a basis for quantitative determination of the drugs. The complexes were found to have 1:1 composition and have stability of the order 10 3 to 10 4 The effect of the concentration reagent, polarity of solvent, interference of excipients have been studied and optimized. Acetonitrile was found to be suitable solvent for the analysis. The methods have been validated in terms of ICH guidelines and applied to the quantification of pharmaceuticals. The variation of slopes of calibration plots and stability constants of the complexes are discussed in terms of structures of the drugs.