Flow injection spectrophotometric determination of isoproterenol with an on-line solid-phase reactor containing immobilized manganese dioxide

This work reports the application of a simple, sensitive, and rapid flow injection system for the spectrophotometric determination of isoproterenol by using a solid-phase reactor containing MnO2(S) immobilized in a polyester resin. The method is based on the oxidation of isoproterenol to produce isoproterochrome, which was monitored at 492 nm. The analytical curve was linear in the isoproterenol concentration range from 1.0 x 10(-5) -2.0 x 10(-4) mol L-1, with a detection limit of 1.7 X 10(-6) mol L-1. The relative standard deviation (RSD) was 0.9%, and an analytical frequency of 60hr(-1) was obtained. The average recoveries varied from 101.0% to 104.2%, evidencing the absence of matrix effect on the flow injection procedure. The effect of excipient substances frequently found with isoproterenol in pharmaceutical formulations, such as lactose, sucrose, starch, poly(ethylene glycol), and sodium chlorine was evaluated by using the proposed flow procedure. None of these substances caused significant interference in the proposed method. The procedure was successfully applied to the determination of isoproterenol in pharmaceutical preparations, and the results were compared with those results obtained by using an ultraviolet (UV)-spectrophotometric method.