The response of thin-film copper (II) ion-selective electrodes based on chalcogenide glassy Cu-Sb-Ge-Se is described according to the soaking time in a 10(-4) M copper (II) solution. The chalcogenide membrane/solution interface has been investigated by using electrochemical impedance spectroscopy (EIS) and Xray photoelectron spectroscopy (XPS) in order to understand the sensing properties. During the first month of the soaking, an alteration of the membrane by a chemical change without alteration of the sensor detection performance has been observed. (C) 2009 Elsevier B. V. All rights reserved.