CALIXARENES IN ELECTROANALYSIS

The use of calix[n]arenes as recognition reagents in electroanalysis is reviewed. Calix[n]arenes (n = 4 to 14) are macrocylic phenol-formaldehyde condensates which may be derivatized at the phenolic oxygen position to produce macrocycles capable of the selective binding of metal cations. Calix[4]arene derivatives having ester, ketone and amide functionality generally exhibit sodium selectivity and the larger calix[6]arenes show a preference for cesium ions. A number of calixarenes have been successfully incorporated into polymeric membrane ion-selective electrodes (including ISFETs). Calixarene-based sodium selective ISEs exhibit excellent sensitivity and selectivity, especially over potassium ions, which has allowed usage of these ISEs in assays of sodium in blood and serum. Calixarene-based ISEs sensitive to potassium, cesium and organic amine ions have also been reported. More recently ISEs and ISFETs sensitive to heavy metal ions such as silver, lead and copper(II) have been fabricated from various sulfur functional group derivatized calix[4]arenes. Potentiometric analytical uses of calixarenes have received most interest to date. However, voltammetric investigations have shown that carbon paste modified electrodes may be prepared with polymeric calixarenes and allow stripping voltammetric determination of lead, copper and mercury simultaneously. Voltammetric studies of calixquinone/hydroquinone and calixarene inclusion complexes have also been reported. Prospects for the future development of calixarenes as ionophoric reagents in electroanalysis are discussed.