Spectrophotometric and titrimetric determination of certain adrenergic drugs, using organic brominating agents

New oxidimetric titrants, bromamine T, dibromohydantoin, N-bromophthalimide, and N-bromosuccinimide, were applied to the determination of ephedrine.HCl, norephedrine.HCl, and methyldopa. Direct potentiometric and visual indicator titration methods as well as back-titration procedures have been developed for their determination. Oxidation of ephedrine and norephedrine produces benzaldehyde, which is extracted from pH 11.0 phosphate buffer with ether or hexane and determined spectrophotometrically at 242 nm. Beer's law is obeyed in the concentration range from 0.2 to 2 mg ephedrine.HCl and from 0.15 to 1.9 mg norephedrine.HCl. Methyldopa is determined titrimetrically and spectrophotometrically. In addition, this drug acts as a self-indicator: Solutions change from colorless to red, which gradually disappears with continuous addition of brominating agent and shaking. Phosphate buffer is used to produce adrenochrome, characterized by its pink color which can be measured at 485 nm in a working range from 40 to 650 micrograms.