Hanan Merey
Prof. of Analytical Chemistry, Faculty of Pharmacy, Cairo University
This paper reports the construction and evaluation of two ion selective electrodes for the determination midodrine hydrochloride (MD) by direct potentiometry in pure drug substance and in tablet formulations. Precipitation based technique was used for fabrication of the first membrane sensor (sensor 1) using phosphotungestate (PT) and dioctylphthalate (DOP), as cation exchanger and solvent mediator, respectively. β-cyclodextrin (β-CD)-based technique with PT as a fixed anionic site in PVC matrix was used for fabrication of the second membrane sensor (sensor 2). The proposed sensors showed fast, stable Nernstian responses of 54 and 57 mV/decade for sensors 1 and 2, respectively, across a relatively wide MD concentration range (1x10-4 to 1x10-1 mol/L and 5x10-5 to 1x10-1 mol/L) for sensor 1 and 2, respectively , in the pH range of 4.5-7.5. Sensor 1 and sensor 2 can be used for three and two weeks, respectively without any measurable change in sensitivity. The suggested electrodes succeeded to determine intact (MD) in the presence of up to 10% of its degradate and displayed good selectivity in presence of common inorganic and organic species.