Potentiometric determination of 8-chlorotheophylline

Two methods are described for the potentiometric determination of 8-chlorotheophylline in aqueous solution. Both methods are based on the reaction of 8-chlorotheophylline with silver ions. In the first, the nitric acid produced in the reaction is titrated with sodium hydroxide. In the second, the 8-chlorotheophylline is titrated directly with silver nitrate in sodium carbonate medium. Both methods give reasonably accurate and reproducible results, and are suitable for the assay of 8-chlorotheophylline in pharmaceutical preparations.