Electrodes formed from the chalcogenide glass, , are selective to cupric copper in concentrated solutions of chloride, bromide, nitrate, and acetate over the concentration range of 10−1 to at least 10−6M copper. Nernstian slopes of approximately 30 mV/decade concentration changes were observed in nitrate and acetate solutions; slopes of 50 mV/decade were observed in 1M chloride and bromide electrolytes. A slope of 40 mV/decade was observed in 0.1M chloride solution. The active phase in the electrode material appears to be “sinnerite” ; data on the sensing mechanism are presented.