POTENTIOMETRIC EVALUATION OF THE ION-SELECTIVE CHARACTERISTICS OF 1,4-BRIDGED CUBYL DIESTER CROWN-ETHERS

Cubane diester crown ethers were tested as ion-selective electrodes in poly(vinyl chloride) (PVC) membranes. The four ionophores studied pro ved to be good K+ neutral carriers, showing Nernstian and near-Nernsti an responses to this ion, in the range 10(-4)-10(-1) M. The fixed inte rferences method was used to determine relative selectivity coefficien ts for all the electrodes. The highest selectivity for potassium relat ive to sodium, lithium, calcium and magnesium ions using potassium tet rakis(p-chlorophenyl) borate (KTpClPB as a resistance modifier and NPO E as a plasticizer was obtained with the 1,4-cubyl diester-25-crown-7 ether ionophore. The effects of KTpClPB on membrane selectivity were a ssessed; its removal was found to increase the selectivity of the four ionophores for potassium relative to cesium, sodium, calcium and magn esium ions with minimal effects on lithium and ammonium ions. The comp ounds tested exhibited a fast Nernstian response to changes in K+ conc entration which was stable to within < 100 muV h-1.