Spectrophotometric Determination of Adrenaline, Phenylephrine Hydrochloride, and Terbutaline Sulfate Using the Gibbs Reagent

A spectrophotometric method has been developed for the determination of certain amine-phenol-containing drugs, namely, adrenaline, phenylephrine hydrochloride, and terbutaline sulfate. The method depends on the formation of new products by the reaction of drugs with the Gibbs reagent (2,6-dichloroquinone-4-chloroamide) in a basic borate buffer medium with a pH value of 11. The products were measured at 475, 652.5, and 547 nm for the aforementioned drugs, respectively. Beer-Lambert law was obeyed in the ranges of 0.3-9.5, 0.5-17, and 0.5-55 mu g/mL with average recovery of 101.10, 99.13, and 99.78% and a relative standard deviation of <= 3.31%, respectively. The method was free from excipient interferences and applied successfully for the assay of the studied drugs in their pharmaceutical formulations. The resulting products were found in the ratio of 1 : 1.