Novel Cesium‐Selective Electrodes Based on Lipophilic 1,3‐Bisbridged Cofacial‐calix[6]crowns

Five bisbridged calix[6]crowns have been investigated as Cs⁺ionophore in PVC membrane electrodes. As ionophores, three 1,3‐bisbridged calix[6]crown‐4‐ethers(I–III), 1,3‐bisbridged calix[6]crown‐5‐ether(IV), and 1,3‐bisbridged calix[6]crown‐6‐ether(V) have been evaluated. The membranes all give good Nernstian response in the concentration range from 1×10⁻⁷to 1×10⁻¹ M of cesium ion. The best detection limits (−loga=7.08–7.36) are obtained for electrode membranes containing 1,3‐bisbridged cofacial‐calix[6]crown‐4‐ethers(I‐III), and the values are the lowest compared with those reported previously. The highest selectivity coefficients [$\rm{ {\rm p}K_{{\rm Cs}^ + ,{\rm j}}^{{\rm pot}} = 5.53({\rm Cs/Na}),}$3.74(Cs/K), 2.63(Cs/Rb)] are obtained for the membrane of 1,3‐bisbridged calix[6]crown‐4‐ether(II), and these values are also the highest compared with previous reports for Cs⁺‐ISEs. The highest selectivity towards cesium ion is attributed to the geometrically cofacial positions of two crown‐ethers in calix[6]crowns in order to provide the complex of cesium ion and eight oxygens of cofacial crowns.