Ionophores in polymeric membranes for selective ion recognition; impedance studies

Synthetic calix[4]arene-crown ionophores for selective Na+ (ionophore L1) and Cs+-ions (ionophore L2) recognition find application in ion-selective membrane electrodes (ISE) for analytical purpose. Selectivity coefficients for the electrodes with compounds L1 and L2 are logKNa,Cspot = −2.6 and logKCs,Napot = −2.4, respectively. Electrodes of two different construction: all-solid-state (ASS) (with conducting polymer layer on glassy carbon or platinum as ion-to-electron transducer) and conventional ion-selective electrode (ISE) (with liquid electrolyte and Ag/AgCl) are presented and their properties and lifetime are being compared. Resistance of PVC membrane with ionophores L1 and L2 were within the range 0.15–1.4 MΩ depending on the type of the outer electrolyte and its concentration. Conductivity of the membranes was in the range 0.7 × 10−8 to 6 × 10−8 Ω−1 cm−1. Warburg coefficients σ were within 0.16 × 104 to 12.7 × 104 Ω s−1/2, dielectric constant values ɛ were in a range 28–60 depending mainly on the type of plasticizer.