Source: pioyi/ion-selective-electrodes/response-of-the-glass-electrode
= Response of the Glass Electrode
The hydrated glass interface is conductive due to the presence of hydrogen cations.
In each interface of the membrane an equilibrium is established:
$$
\ce{H^+(solution) + Gl-(glass) <=> H^+Gl^-(glass)}
$$
A potential difference is again caused due to the difference in ionization.
The equilibrium's position depends on the concentration of $H^+$ in each interface.