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

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-pbenzoquinone (bromanil), in the presence of borate buffer solution of pH 9 to form ncharge-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.cm for the Spectrophotometric Determination of Catecholamines in ... 2 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. INTRODUCTION Catecholamine drugs are aromatic vicinal-diols that consist of amines attached to a benzene ring bearing two hydroxyl groups (catechol). The catecholamines are primary synthesized in vesicles of the chromaffin cells in the adrenal medulla. These drugs are widely used in the treatment of bronchial asthma, hypertension, Parkinson’s disease, drug abuse, Schizophrenia and myocardial infarction. Several spectrophotometric methods have been applied to assay of catecholamines as cited in the literature including derivatization reaction with organic reagents such as o-phenanthroline, diazodized nitroaniline, ninhydrin, thiosemicarbazide chloramine-T, phenylenediamine, and inorganic reagents like iodine, ammonium metavanadate metaperiodate, cerium(VI) nitrate, neotetrazolium chloride. Other methods have been adapted to stopped flow technique, flow injection analysis, HNMR spectroscopy, coloumetric titration and cyclic voltametry. The charge transfer complex reaction has been used for determination of catecholamine by using various organic reagents such as chloranil, DDQ and fluoranil. The present paper describe simple, sensitive, and accurate spectrophotometric determination of dopamine hydrochloride, methyl dopa and L-dopa using charge transfer complex formation reaction in aqueous medium with bromanil in the presences of solution of pH 9 borate buffer. EXPERIMENTAL Apparatus: All absorption measurements were made using Shimadzu UV-210 double beam spectrophotometer with 1-cm matched optical silica cells. Heating of solutions was carried out on waterbath (Forst Instruments LTD). The pH readings were made using a PW 9420 pH-meter supplied with an electrode type CE10-12 pH. Weighing was carried out on a balance type of Sartorius No. 6407.