Calix[4]arene Derivatives: Efficient Ionophores for Silver(I) Ion Sensors

Abstract

Abstract Calix[4]arene derivatives with four imine units at the upper rim and different spacers between two calixarenes were employed as highly promising lipophilic neutral carriers to prepare a series of silver-selective electrodes. These calix[4]arenes possess a flexible conformation for rapid ion-exchange across the PVC membrane to provide good response for silver ions. The prepared silver ion-selective electrodes exhibited near-Nernstian responses for silver ions over a wide concentration range of 1.0 × 10−1–1.0 × 10−5 M with a very low detection limit of ∼10−6 M. The potentiometric responses were independent of the pH of the test solution over wide acidic pH range. The effect of various plasticizers on the electrode characteristics was also examined, and bis(2-ethylhexyl) sebacate proved to be the most suitable, since it provided the best slope and other electrode characteristics. High selectivity for Ag+ over Hg2+, Na+, and many other cations was found. The high selectivity for silver ions is mainly attributed to host–guest interactions that occur between the silver and appended groups of calix[4]arene derivatives. The electrodes were used as indicator electrodes in potentiometric titration involving silver ion, and provided a simple method for the determination of Ag+ and Cl− in water samples.