Flow injection discrimination of the chloride interference with Cu(II) electrode function of chalcogenide based solid-state copper ion-selective electrodes

The paper outlines the analytical applicability of the flow injection dynamic approach to suppressing the chloride interference with chalcogenide based Cu-ISEs on the example of two different membrane compositions of the now-injection potentiometric (FIP) detectors, Cu2-xSe and CuAgSe. The presence of chloride in the injected copper(II) standards is manifested by the appearance of two consecutive peaks in the output transient signal, the first of which, below the baseline, proves to be reciprocally dependent on the C-Cu(II)/CCl- ratio in the sample. Through a detailed examination of the factors controlling this complex profile of the output signal, conditions have been found, under which a kinetic separation of the reactions governing the dynamic response to Cu(II) in the presence and absence of chloride becomes possible. The new approach is technically simple, highly reproducible and does not perturb the sample speciation. Cu(II) concentrations down to 5 x 10(-6) M in non-buffered solutions and 1 x 10(-9) M in copper-methionine ion-buffers can be determined in the presence of up to 1 M KCl. A mechanism of the chloride discrimination is proposed. According to this mechanistic scheme the chloride discrimination is mainly controlled by two inter-dependent events occurring in the detector cell: (i) the continuous increase of the C-Cu(II)/CCl- ratio at the membrane surface, resulting from the fast desorption of chloride and (ii) the ability of the ion-selective membrane to rapidly respond to this change. The postulated mechanistic scheme is supported by analysis of the transient signals obtained for both Cu(II) and Cl- ions employing a multi-ion sensor detector with Cu2-xSe- and AgCl-electroplated membranes incorporated in series. (C) 1998 Elsevier Science B.V.