Spectrophotometric determination of some pharmaceutical piperazine derivatives by charge-transfer and ion-pair complexation methods

Simple and sensitive spectropliotometric methods are described for the assay of three piperazine derivatives ketoconazole, trimetazidine hydrochloride and piribedil based on cliarge-transfer and ion-pair complexation reactions. The first method is based on the reaction of the basic drug with iodine as o-acceptor in dry 1,2-dichloroethane to form a yellow colour due to the formation of charge-transfer complex showing maximum absorbence at 363, 364 and 359 nm for ketoconazole, trimetazidine hydrochlorid and piribedil, respectively. The second method is based on the reaction of basic drug with bromocresol green (BCG) in dry 1,2- dichloroethane to form a stable yellow coloured complex with maximum absorbance at 407, 408 and 410 nm for ketoconazol, trimetazidine hydrochloride and piribedil, respectively. Beer's law was obeyed for both methods and the relative standard deviations were found to be less than 1%. The two methods can be applied for the analysis of tablets and cream, with no evidence of interference from excipients. A more detailed investigation of the complex was made with respect to its composition association constant and free energy cliange.