Determination of cinnarizine in pharmaceutical preparations by spectrophotometry, atomic absorption spectrometry and potentiometry

New methods are developed for the determination of cinnarizine in various dosage forms. They are based on the reaction of cinnarizinium cation with cobalt tetrathiocyanate anion, whereby a sparingly soluble blue 2:1 drug: reagent ion-pair complex is quantitatively formed. The complex is (a) extracted with nitrobenzene and spectrophotometrically measured at 622 nm; (b) extracted with nitrobenzene and nebulized in an air-acetylene flame for atomic absorption spectrometric monitoring of cobalt at 242.5 nm; and (c) dispersed in a PVC membrane plasticized with 2-nitrophenyloctyl ether and used as a sensor for direct potentiometric determination of the drug. Optimum reaction conditions and performances of the three analytical techniques are evaluated and compared. At the 25 mg level of cinnarizine, the three methods give results with equal accuracy and precision. The average recovery is 98-99\% of the nominal and the mean standard deviation is 0.7\%. No significant interferences are caused by drug excipients and diluents.