Copper ion-selective chalcogenide glass electrodes. Analytical characteristics and sensing mechanism

Abstract

New copper ion-selective electrodes based on chalcogenide glasses, CuxAg25-xAs37.5Se37.5, display high copper(II) ion sensitivity with Nernstian response in the range pCu 1-6, short response time, high selectivity, potential stability and reproducibility. These electrodes are 10-30 times more sensitive in strongly acidic media than crystalline copper ion-selective sensors and are superior to the copper(I) selenide electrode in selectivity and resistance to acids and oxidation. A model is proposed to explain the ion sensitivity of these chalcogenide glass sensors. The sensitivity depends on direct exchange of copper(II) ions between solution and the modified surface layer of the glass. The modified surface layer is formed as a result of partial destruction of the glass network on soaking in solution; its atomic density is 2.0-2.5 times less than that of the original glass. The structural defects and hollows make fast copper(II) ion migration within the modified surface layer possible. Exchange sites in this layer can be formed by both disproportionation and oxidation of copper(I) in the glass network, as well as by diffusion of copper(II) ion from solution in the case of glasses with low copper content. Experimental confirmation of this model is provided by x-ray, photo-electron and scanning Auger electron spectroscopy. © 1986.