Sodium-selective electrodes based on triester monoacid derivatives of p-tert-butylcalix[4]arene. Comparison with tetraester calix[4]arene ionophores

The performance of sodium selective electrodes based on the triethylacetate and trimethylacetate monoacid derivatives of p-tert-butylcalix[4]arene is described together with their tetraester analogues. All electrodes showed slopes in excess of 50 mV dec−1 (53.5–56 mV dec−1) and lifetimes of at least 35 days. Virtually no difference in selectivity between the monoacid derivatives and the tetraesters was found. pH stability studies showed that the monoacid derivatives gave best performance at neutral pH but at alkaline pH (>8) there was a reduction in response which did not occur with the tetraesters. This difference in behaviour may be due to deprotonation of the monoacid derivatives at high pH values at the aquo-membrane boundary prior to complexation.