Colorimetric procedure for the microdetermination of the antibilharzial drug praziquantel and its applications to pharmaceutical formulations

A procedure for the colorimetric assay of praziquantel has been developed. The method is based on the formation of charge-transfer complexes with p-ch loranil (I), dichloronitrophenol (II), 2,3-dichloro-5,6 dicyano-p-benzoquin one (III), 7,7,8,8-tetracyanoquinodimethane (IV) and tetracyanoethylene (V) as pi -acceptors to give highly coloured species. The coloured products ar e measured spectrophotometrically at 550, 425, 460, 844 and 393 mn for I, I I, III, IV and V, respectively. Optimization of the different reaction cond itions is described. The colour system obeyed Beer's law in non-aqueous med ia in the concentration range 2.0-48 mug ml(-1). It was stable for at least 4.0 h. The detection limit was found to be 0.6 mug ml(-1). Applications of the procedure to the analysis of various pharmaceutical samples gave repro ducible and accurate results. Further, the validity of the procedure was co nfirmed by applying the standard addition technique. The total average reco very was 100.2%.