Potentiometric determination of some common alkaloids with a picrate-selective electrode

Potentiometric methods are described for the determination of alkaloids, based on the formation of insoluble alkaloid picrate salts, using a picrate ion-selective indicating electrode. Micro-amounts of strychnine, papaverine, quinine and cocaine were determined by direct potentiometry and titrimetrically, using Gran plots, with average errors of about 4% and 2%, respectively. The method was successfully applied to pharmaceutical preparations.