Determination of difenidol hydrochloride by capillary electrophoresis with electrochemiluminescence detection

A novel and sensitive method for the determination of difenidol hydrochloride has been established using capillary electrophoresis coupled with end-column electrogenerated chemiluminescence (ECL) detection, based on the ECL reaction of tris(2,2′-bypyridine)ruthenium(II) (Ru(bpy)32+) with the tertiary amino groups of the difenidol analyte. Parameters that affect separation and detection were optimized. Calibration curve was linear over the range from 1 × 10−6 M to 6 × 10−5 M with a detection limit of 1 × 10−7 M (S/N = 3). Separation of difenidol hydrochloride from clomifene citrate and lidocaine was achieved using the proposed method. This method was successfully utilized to the assay of the active ingredients of the “difenidol hydrochloride” tablets and to the investigation on the interaction of difenidol hydrochloride with hemoglobin. The number of binding sites and the binding constant were estimated as (11.2 and 2.5) × 103 M−1, respectively.