SPECTROPHOTOMETRIC INVESTIGATION OF METOPROLOL-BENZYL ORANGE REACTIONAND ITS APPLICATION TO THE ASSAY IN PHARMACEUTICAL DOSAGE FORMS

A sensitive spectrophotometric method for the determination of metopro lol tartrate in tablets and ampoules is presented. Using spectrophotom etric measurements, it was found that metoprolol tartrate and benzyl o range form a chloroform soluble ion-pair complex with an absorption ma ximum at 401 nm. The composition of the ion-pair complex was determine d by applying Job's method to equimolar solutions of metoprolol tartra te: benzyl orange (1:2); molar absorptivity 7.39x10(3) mol(-1) cm(-1) Extraction of the ion-pair complex in chloroform was accomplished easi ly at a Britton-Robinson's buffered optimum pH = 5.2, mu=0.1 mol/dm(3) . The relative stability constant, calculated according to the method of Sommer and Job's non-equimolar solutions, was log K= 9.72 (avg. val ue). Beer's law was obeyed up to 3.42 mu g/ml of metoprolol tartrate ( the detection limit was also 3.42 mu g/ml). The precision of the metho d was checked at three different concentrations. The RSD (n = 7) varie d from 0.51 to 2.03%. Reproducibility was examined by analysing Lopres or (R) tablets and ampoules. Recoveries varied from 99-101%. The repor ted method, applied to the assay of metoprolol tartrate in tablets and ampoules, gives precise and reproducible results.