306-75 Copper Mono ION Selective ElectrodeION selective electrode for testing plating baths, water and applications where greater accuracy is required. About Copper Mono ION Selective Electrode. This electrode requires a separate reference electrode. Suitable for applications where greater accuracy is required (especially when ION levels are low). Applications Plating baths Water Specifications Dimensions: 120 x 12mm Concentration: 1M 5 x 10 8M Lower Limits (ppm): 0. 3 Ref. Electrode: R2 Temp