RESUMO
Two new potentiometric methods for determination of famotidine in pure form and in its pharmaceutical tablet form are developed. In the first method, the construction of plasticised poly(vinyl chloride) (PVC) matrix-type famotidine ion-selective membrane electrode and its use in the potentiometric determination of famotidine in pharmaceutical preparations are described. It is based on the use of the ion-associate species, formed by famotidine cation and tetraphenyl borate (TPB) counterion. The electrode exhibited a linear response for 1 x 10(-3)-1 x 10(-5) M of famotidine solutions over the pH range 1-5 with an average recovery of 99.26% and mean standard deviation of 1.12%. Common organic and inorganic cations showed negligible interference. In the second method, the conditions for the oxidimetric titration of famotidine have been studied. The method depends on using lead(IV) acetate for oxidation of the thioether contained in famotidine. The titration takes place in presence of catalytic quantities of potassium bromide (KBr). Direct potentiometric determination of 1.75 x 10(-2) M famotidine solution showed an average recovery of 100.51% with a mean standard deviation of 1.26%. The two methods have been applied successfully to commercial tablet. The results obtained reveal good percentage recoveries, which are in good agreement with those obtained by the official methods.