Potentiometric response of ion-selective membranes with ionic liquids as ion-exchanger and plasticizer

Room temperature ionic liquids (RTILs), based on imidazolium, pyridinium and phosphonium cations, have been studied as an anion-exchanger and plasticizer for poly(vinyl chloride) (PVC)-based potentiometric ion-selective membranes. 1-Methyl-3-octylimidazolium chloride (MOImCl) and trihexyltetradecylphosphonium chloride (THTDPCl) can plasticize PVC to form flexible ion-sensing membranes. PVC–MOImCl membrane without additional ionophore and ion-exchanger demonstrated Nernstian response to sulfate ion with slope of 29.1 mV/decade in the concentration range of 10−5 to 10−1 M. The ionophore-free membrane showed good selectivity toward SO42− over Cl−, ClO4−, NO3− and SCN−. PVC–MOImCl-based electrode have fast response time within 10 s and wide pH independent range (3–10). The proposed electrode was used for the determination of sulfate in drinking water samples with satisfactory results. On the other hand, PVC–THTDPCl membrane exhibited stable and Nernstian response to different anions and the selectivity followed the Hofmeister series. Additionally, THTDPCl was found to be a suitable alternative to the traditional anion-exchanger, TDMACl and can be used as ionic additives in ionophore-based ion-selective sensors.