Eman Elzanfaly

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 56 mV/decade for sensors 1 and 2, respectively, across a relatively wide MD concentration range (1 × 10–4 to 1 × 10–1 mol/L and 5 × 10–5 to 1 × 10–1 mol/L for sensor 1 and 2, respectively) in the pH range of 5–7. 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 degradation product and displayed good selectivity in presence of common inorganic and organic species.

This paper presents a comparative study between four sensors
constructed to determine benoxinate hydrochloride (BX) in the presence of its hydrolysis
induced degradation product using different ion association complexes and plasticizers.
Precipitation based technique was used for sensors fabrication. The BX complexes with the
cationic exchangers; BX- reinikate, BX-tetraphenylborate, BX-phosphotungestate, and BXtetrakis
were obtained in situ by soaking the PVC membranes in 1×10-2 BX solution.
Dioctylphthalate and nitrophenyl octyl ether were used as solvent mediators. The proposed
sensors showed fast, stable Nernstian responses across a relatively wide BX concentration
range (5×10-5 to 10-1 M) in the pH range of 4-6. The suggested sensors could be used for
several weeks without any measurable change in sensitivity. They displayed good selectivity
for BX in presence of its degradation product, common inorganic and organic species. The
proposed sensors were successfully applied for the determination of BX in pure powder form
and eye drops where good recoveries were obtained.