USING PARACETAMOL HYDROLYSIS IN THE SPECTROPHOTOMETRIC DETERMINATION OF DOPAMINE HYDROCHLORIDE AND METHYLDOPA BY OXIDATIVE COUPLING REACTIONS

A simple and accurate spectrophotometric method was developed for the determination of dopamine hydrochloride and methyldopa. This method depends on the oxidative coupling reaction of these compounds for paracetamol hydrolysis. It utilizes a potassium bromide-bromate mixture as an oxidative agent in a basic solution and CPC as a surfactant. A violet and blue color is formed for both dopamine hydrochloride and methyldopa, with maximum absorption at wavelengths of 577 and 596 nm, respectively. The method followed Beer’s law with a range of (1.0-17.5) and (3.0-25.0) µg/mL, and their molar absorptivity was (9.33×103) and (9.56×103) L/mol.cm for the above compounds, respectively. The recovery of the method was 100.65% and 102.30%, while the relative standard deviation was 0.70% and 0.61% for the studied compounds. The LOD values of dopamine hydrochloride and methyldopa were (0.1631) and (0.1056) µg/mL, and the LOQ values were (0.5436) and (0.3521) µg/mL, in that order. Pharmaceutical preparations of the two drug compounds were well applied using the method.