Application of calixarene ionophores in PVC based ISEs for uranium detection

A lower rim functionalised calixarene molecule 5,11,17,23-tetra-tert-butyl-25,27-bis(hydroxy)-26-(ethoxycarbonylmethoxy)-28-(diethyl carbamoyl-methoxy) calix[4]arene, which was originally developed for solid phase extraction of trace uranium from environmental and industrial waste water, is tested as a possible ionophore in ion selective electrodes (ISEs). PVC based membranes containing the calix[4]arene were used in experiments to test the characteristics and viability of these sensors. The electrodes gave more stable potential readings when used around neutral pH 5.5–8.5. Extraction experiments using the PVC membranes showed that the calix[4]arene complexed with the uranyl species end extracted it from the test solutions most effectively at around pH 7.0. The limit of detection for uranium species, around 1 ppm under normal conditions, was avoided by preconditioning the membranes at high pH. The effect of testing for uranium selectivity amongst a matrix of cations and anions in a simulated waste solution showed that interference was significant. As we are at the beginning of this research, suggestions for further work on these electrodes are made in light of recent reports of work in this field.