Spectrophotometric determination of some phenolic sympathomimetic drugs through reaction with 2,6-dihaloquinone chlorimides

A spectrophotometric procedure is described for the determination of three phenolic sympathomimetic drugs: etilefrine hydrochloride, prenalterol hydrochloride and ritodrine hydrochloride. The method involves the use of 2,6-dichloro- and 2,6-dibromoquinone chlorimides as chromogenic reagents. The phenolic drugs produce a blue color, peaking from 610 to 630 nm. The colors produced obey Beer's law and are suitable for the quantitative determination of the named compounds. The molar ratios of the reactions were established and a proposal for the reaction pathway is given. The procedures described were applied successfully to the determination of the compounds in their dosage forms. The results showed that the proposed procedures compared favourably with the reference methods and satisfactory sensitivity, accuracy and precision (SD < 0.1 μg ml−1) were noted. Detection limits are typically 0.2–0.4 μg ml−1. Other advantages of the procedures are their simplicity and speed.