Patent ID: 7276142

Claim:
A combination glass pH electrode including a sensing electrode, a reference electrode possessing a standard potential, an outer tube having a liquid junction, an inner tube centrally located within the outer tube and connected to the outer tube by a top seal and a bottom seal, a reference electrolyte compartment located between the inner and outer tubes and the top and bottom seals having an opening in the outer tube, and reference electrolyte within the reference electrolyte compartment, wherein the improvement comprises: incorporation of a reference electrolyte compartment vent wherein the opening to the reference electrolyte compartment is covered with an elastomeric septum closure that is perforated to permit insertion of a tube which by reason of its small inside diameter compared to its length serves to minimize diffusion of moisture into or out of the reference electrolyte compartment yet serves to admit sufficient air to allow electrolyte flow from the reference electrolyte compartment through the liquid junction under the influence of gravity; whereby the reference electrolyte is kept constant and the standard potential of the reference electrode is thereby stabilized; whereby the combination glass pH electrode needs no calibration for up to two years.