Surface studies on precipitate-based cyanide electrodes

Silver iodide-based electrodes allow indirect measurements of cyanide. Potentiometric investigations and theoretical studies have suggested that a corrosion process is responsible for this cyanide response. Surface analytical methods of providing information at different depths are used to investigate mixed membranes of silver iodide/silver sulphide and pure silver iodide membranes. The results prove that in the surface corrosion process the iodide content of the mixed membrane surface decreases. Further, the membrane loses silver sulphide particles from its surface. Finally, a layer enriched with readsorbed iodide is formed on the outermost surface of the membrane. The composition of the surface layer depends on pH and buffer capacity because of the different fluxes of ions observed in the surface layer.