FIA TITRATIONS OF EPHEDRINE IN PHARMACEUTICAL FORMULATIONS WITH A PVCTETRAPHENYLBORATE TUBULAR ELECTRODE

A flow injection system for the titration of ephedrine in pharmaceutic al products with potentiometric detection was developed. For this purp ose a tetraphenylborate tubular electrode was constructed. The electro de was prepared without inner reference solution and with a PVC membra ne based on tetrapentylammonium tetraphenylborate as ion exchanger and 2-nitrophenylphenyl ether as mediator solvent. Its operational charac teristics were evaluated in a low dispersion manifold and compared wit h more conventionally shaped electrodes using the same sensor. In the pH range 2.5-11.5, the electrodes showed linear response between 3.8 x 10(-6) and 0.1 M with a slope of -56.4 mV/log[BPh4]. Ephedrine determ inations in pharmaceutical products were carried out in a single chann el manifold with a mixing chamber incorporated and using the tubular e lectrode as detector. Recovery rates of 98.6 +/- 2.5% were obtained in the analysis of tables, nasal drops and syrups with a sampling rate o f about 60 h(-1).