Spectrophotometric Determination of Catecholamines in Pharmaceutical Preparations Via Charge Transfer Complex Formation Using Bromanil Reagent

ABSTRACT<br /> A simple, rapid and sensitive spectrophotometric method has been developed for the determination of trace amounts of catecholamine drugs (dopamine, levodopa and methyldopa). The method is based on the interaction of these drugs in aqueous medium with tetrabromo-p-benzoquinone (bromanil), in the presence of borate buffer solution of <br /> pH 9 to form n- charge-transfer complexes with maximum absorbance at 350, 366 and 368 nm for methyldopa, levodopa and dopamine respectively. Beer’s law was obeyed in the range of 1-25, 0.8-30 and 1-30 g/ml with molar absorptivities 8075, 8500 and 3475 l.mol-1.cm-1 for the above drugs respectively. The accuracy (average recovery%) of method was found better than 99% and the precision (RSD) was less than 3%. The nature and stability of bromanil complexes with the above mentioned drugs were studied. The method was successfully applied for the assay of methyldopa, levodopa and dopamine in some of their pharmaceutical formulations, and the results compared favorably with British pharmacopoeia and the standard addition technique. The common excipients used additives in pharmaceutical, do not interfere with the proposed method.