MACROCYCLIC POLYETHER TETRALACTAMS .4. POTENTIOMETRIC EVALUATION OF ION-SELECTIVE CHARACTERISTICS WITH ALKALINE-EARTH CATIONS

Macrocyclic polyether dioxatetralactams have been evaluated as ion-sel ective electrodes in poly(vinyl chloride) membranes. The six ionophore s studied proved to be very good Ca2+ neutral carriers showing good di scrimination against Mg2+ and alkali-metal cations with Nernstian and near-Nernstian responses to these ions in the range 10(-5)-10(-1) mol dm(-3). The fixed interference method was used to determine relative s electivity coefficients for all the electrodes. The highest selectivit y for calcium relative to potassium, sodium, lithium, zinc and magnesi um ions using potassium tetrakis(p-chlorophenyl)borate as a resistance modifier and 2-nitrophenyl octyl ether as a plasticizer was obtained with ionophore 6 which was found to be comparable in performance to th e model calcium carrier ETH 129. The ionophores tested exhibited a fas t Nernstian response to changes in Ca2+ concentration which was stable to within < 200 mu V h(-1).