Abstract: A novel series of chalcogenide glass compositions that are relatively highly selective for a specific ion in solution. When utilized as a sensing element for electrodes or similar analytical devices, a modified surface layer is formed on the surface of the glass in contact with the test solution. The surface layer being characterized by a surface ionic conductivity ranging from 10.sup.-7 to 10.sup.-2 S/cm, a diffusion coefficient ranging from 10.sup.-11 to 10.sup.-6 cm.sup.2 /s and having a ratio of electronic to ionic conductivity within the modified surface layer of not more than 1.0. Specific compositions having these unique morphology and transport properties are disclosed for the detection of cadmium, silver, thallium, mercury, copper and lead.