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 chalcog enide based Cu-ISEs on the example of two different membrane compositi ons of the now-injection potentiometric (FIP) detectors, Cu2-xSe and C uAgSe. The presence of chloride in the injected copper(II) standards i s 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. Thro ugh a detailed examination of the factors controlling this complex pro file of the output signal, conditions have been found, under which a k inetic separation of the reactions governing the dynamic response to C u(II) in the presence and absence of chloride becomes possible. The ne w approach is technically simple, highly reproducible and does not per turb 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-b uffers can be determined in the presence of up to 1 M KCl. A mechanism of the chloride discrimination is proposed. According to this mechani stic scheme the chloride discrimination is mainly controlled by two in ter-dependent events occurring in the detector cell: (i) the continuou s increase of the C-Cu(II)/CCl- ratio at the membrane surface, resulti ng from the fast desorption of chloride and (ii) the ability of the io n-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 det ector with Cu2-xSe- and AgCl-electroplated membranes incorporated in s eries. (C) 1998 Elsevier Science B.V.