Selective potentiometric determination of zolpidem hemitartrate in tablets and biological fluids by using polymeric membrane electrodes

The construction and electrochemical response characteristics of 4 polymeric membrane sensors were investigated for potentiometric determination of zolpidem hemitartrate. The construction of the 4 sensors was based on the formation of ion-pair complexes between the drug cation and ionic sites in the ratio of 1:2, respectively. Two of the sensors were constructed by using ammonium reineckate or ammonium tungstate as the fixed ionic site in a polymeric matrix of polyvinyl chloride (PVC) (sensors 1 and 2). Linear responses over the concentration range of 10(-5)-10(-3)M, with cationic slopes of 30 and 30.7 mV per concentration decade, were obtained by using sensors 1 and 2, respectively. The third sensor was fabricated by using PVC carboxylate (PVC-COOH). The dissociated COOH groups in the PVC-COOH act as a mediator and/or ionic site. A linear response was obtained over the concentration range of 10(-5)-10(-2)M with a cationic slope of 29 mV per concentration decade. Sensor 4 was fabricated by using 2,6-didodecyl-beta-cyclodextrin as the ionophore, polyurethane (Tecoflex) as a polymeric matrix, and potassium tetraphenyl borate as the ionic site; it showed a linear response over the concentration range of 10(-7)-10(-2)M with a cationic slope of 28.9 mV per concentration decade. The direct potentiometric determination of zolpidem hemitartrate in pure forms by using the 4 proposed sensors gave average recoveries of 98.5+/-0.7, 99.4 +/-0.2, 100.7+/-0.10, and 99.8+/-0.1% for sensors 1-4, respectively. The results obtained by the proposed procedures were statistically analyzed and compared with those obtained by using a reported method. The 4 proposed sensors were also applied successfully to the determination of the drug in tablets and in biological fluids. Average recoveries obtained by using sensors 1, 2, 3, and 4 for drug assay of tablets were 99.6+/-0.6, 100+/-0.7, 99.7+/-0.4, and 99.5+/-0.8%, respectively. The presence of tablet excipients did not interfere with the determination of the drug or with the accuracy and precision of the 4 proposed methods. The methods were also used to determine the drug in the presence of its degradates and thus could be used as stability-indicating methods.