Determination of formal complex formation constants of various Pb2+ ionophores in the sensor membrane phase

Formal complex formation constants of seven ionophores with Pb2+ and a seri es of interfering cations have been determined in the organic membrane phas e. To this purpose, potentiometric selectivities of the target ions relativ e to tetramethylammonium are compared for ion-exchanger- and ionophore-base d ion-selective electrode membranes. Furthermore, information on the stoich iometry of the complexes formed is obtained from measurements with two memb ranes of different ionophore concentrations. Surprisingly, the results show that ionophores having thioamide are less efficient in coordinating Pb2+ t han corresponding ones with oxamide. The formal complex formation constants found are in excellent agreement with those determined by bulk optode meas urements. A generally applicable method is proposed to gain more insight wi th a view to designing ligands and optimizing sensor membrane compositions. (C) 1999 Elsevier Science B.V. All rights reserved.