Long-Life Reference System - The PHE-18 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 the 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. Unique Glass Membrane - The PHE-18 pH electrode uses a spear glass membrane, which is ideal for testing semi-solid samples and can be used to test high-temperature samples (up to 176°F). The electrode uses a BNC connector, compatible with all labForce® pH meters.