Different spectrophotometric procedures have been reported for determination of PEH including the formation of ion-pair complexes between the drug and alizarine, alizarine red S, alizarine yellow G or quinalizarine [14], ninhydrin in sulfuric acid [15], nitrobenzene derivates in acetonitrile medium [16], oxidative coupling with 4-aminoantipyrine in the presence of potassium ferricyanide or sodium periodate [17,18], diazotized p-nitroaniline or 2-aminobenzothiazol in alkaline medium [19,20], forming a charge transfer complex with
chloranil or haematoxylin in alkaline medium [21,22]= 7and[23].uranyl (II) ion forming a complex at pH.