Spectrophotometric determination of certain vicinal dihydroxybenzene derivatives in pharmaceutical preparations

A simple, rapid and sensitive spectrophotometric method for the assay of ce rtain adrenergic drugs, [pyrocatechol (PC), levodopa (LD), methyldopa (MD) and dopamine (DP)] is described. The method involves the oxidation of o-dih ydroxybenzene derivatives by K2CrO4 followed by oxidative coupling with sul fanilic acid (SPA), leading to the formation of a red or violet colored pro duct having maximum absorbance at 490 - 495 nm for LD, MD and DP or at 560 nm for PC. This method has been successfully applied to the determination o f LD, MD and DP in tablets and injections of pharmaceutical preparation. Th e common excipients do not interfere with the proposed method. A statistica l comparison of these results with those of a reported method shows good ag reement and indicates no significant difference in precision.