Polymeric Membrane Anion-Selective Electrodes Based on Diquaternary Ammonium Salts

Hydrophobic diquaternary ammonium salts were used as ionophores to develop polymeric membrane ion-selective electrodes. These compounds had two quaternary ammonium groups separated by either an ethylene or a propylene group. When the two positively charged nitrogens were separated by a chain of two carbon atoms, the resulting electrodes exhibited an anion selectivity pattern that deviated from the Hofmeister series. These electrodes were highly selective for Iodide, showed Nernstian response, and were stable over at least 1 month. When the length of the chain that separated the two quaternary nitrogens was increased to three carbon atoms, the selectivity of the prepared electrodes was that predicted by the Hofmeister series. This Is the same selectivity pattern obtained with previously reported electrodes based on monoquaternary ammonium derivatives. The reported data suggest that the distance separating the positively charged nitrogens in diquats is crucial in obtaining electrodes with unique selectivity properties.