Stopped-flow fluorimetric determination of theophylline in pharmaceutical preparations
The reaction of theophylline with cerium(IV) has been applied to the kinetic-fluorimetric determination of theophylline using a simple and versatile modular stopped-flow system. The method is based on the monitoring of the variation in the fluorescence intensity during the formation of a 1 : 1 compound between the oxidation product of theophylline and cerium(III). The stopped-flow technique provides the data required to determine the reaction rate from each kinetic curve in only 8 s. The linear range of the proposed method is 1–250 µg ml–1 of theophylline and the detection limit is 0.95 µg ml–1. Within- and between-assay precision data have been obtained. The stopped-flow method has been satisfactorily applied to the determination of theophylline in various pharmaceutical preparations. Analytical recoveries are in the range 95.0–102.0%. The results obtained show that the stopped-flow technique is suitable for routine pharmaceutical analysis.