US Patent 7276142 Combination pH electrode with stable standard potential

Disclosed are combination glass pH electrodes, the standard potential of which is stabilized by means one or more of the following structural modifications:(a) incorporating a noble metal internal element in the pH half-cell;(b) incorporating a noble metal internal element in the reference half-cell;(c) incorporating an internal pH bulb electrolyte with stable pH and oxidation-reduction potential;(d) incorporating an homogenous reference electrolyte with stable oxidation-reduction potential and equitransferent salt;(e) incorporating a liquid junction composed of a porous, inert material;(f) incorporating a reference electrolyte compartment vent;(g) incorporating a storage sleeve, with or without an absorbent medium located therein.