Spectrophotometric determination of catecholamines based on their oxidation reaction followed by coupling with 4-aminobenzoic acid

A sensitive and simple spectrophotometric method for the determination of dopamine, methyldopa, levodopa and catechole in either pure form, pharmaceutical formulations and in water is described. The method is based on their oxidation reaction with periodate followed by oxidative coupling with 4-aminobenzoic acid at pH 4 leading to the formation of colored products. The calibration graph was linear in the range of 0.20-18.00 mg L-1, 0.10-20.00 mg L-1, 0.10-20.00 mg L-1 and 0.10-13.00 mg L-1 for dopamine, methyldopa, levodopa and catechole, respectively. Analytical data for determination of the pure compound is presented together with the application of the proposed method to the analysis of some pharmaceutical formulations and water samples. The results compared favorably with reported methods.