A perchlorate-selective membrane electrode based on a Cu(II) complex of the ligand 1,4,8,11-tetra(n-octyl)-1,4,8,11-tetraazacyclotetradecane

The new cyclic polyazacycloalkane 1.4,8,11-tetra(n-octyl)-1,4,8,11-tetraazacyclotetradecane (L1) was synthesised and the copper(II) complex Cu(L1)]2+ characterised. Different electrodes were prepared using the Cu(L1)]2+ complex as ionophore, PVC as plastic matrix and o-nitrophenyl octyl ether (NPOE), bis(2-ethylhexyl) sebacate (BEHS) or dibutyl phthalate (DBP) as plasticizers. The electrode containing DBP showed a Nernstian response over a wide pH range and a fast response time (ca. 3 s) whereas NPOE and BEHS gave near-Nernstian slopes. Selectivity coefficients for the different anions with respect to perchlorate were calculated. The response of the electrodes basically followed the Hofmeister sequence, suggesting that interaction of the ionophore with the anions is via electrostatic forces rather than due to anion coordination to the axial sites of the square-planar Cu(L1)]2+ complex.