Ionic Liquids Based Polymeric Membrane Drug Sensors

Background: Application of room temperature ionic liquids (RTILs) in making potentiometric drug sensors is a new strategy to improve the response mechanism. The response of the sensors generally depends on the polymeric membrane ingredients; amount of sensing material, type of plasticizer and ionic additive. Sensing element of a drug sensor which is the most important component of the membrane can be an ion-pair complex or a molecularly imprinted polymer (MIP). In the potentiometric sensors, drug molecules should be able to form a cationic or anionic species to exchange with the similar species in interaction with the sensing element placed in the membrane. Hydrophobicity of the drug and the membrane properties affect the extraction of the drug ions from aqueous phase to the organic layer of the membrane. Rather recently, ionic liquids have found important roles as ionic additives to help better extraction of these organic ions. In addition, due to their particular electrochemical properties, they improve the membrane conductivity which may be more important in case of MIP-based membrane sensors. Also, since they better compatibility with polymers, they plasticize the membrane more properly and improve the performance of the sensor. Miscibility of RTILs with water is the key factor to limit their selection. RTILs can be water-immiscible or hydrophobe compounds depending on the type of cationic and anionic bases. Objective: From the early introduction of the potentiometric methods up to now, there are many reports on PVC membrane sensors for the wide range of pharmaceutical compounds. However, this review considers those ones which used ionic liquids in the composition of the membrane.