Long-Life Reference System - The PHE-13 pH electrode uses a long-life reference system, composed of a glass, AgCl and a reference silver wire. The top end of the slim glass tube is stuffed with cotton, which prevents the reaction between AgCl and electrolyte when the temperature changes. It improves the stability of reference electrode and extends the service life of the electrode. Polymer Electrolyte - The solid polymer electrolyte makes the electrode hard to contaminate and maintenance-free. Special Glass Membrane - The PHE-13 pH electrode uses a spear sensor tip, ideal for directly testing semi-solid samples like soil. This is a replacement electrode for the TS-S200 portable pH meter. Also compatible with all labForce® pH meters.