Compute the cell potential:

To compute the cell potential, it could be assumed that the SCE is more positive than the glass electrode. Therefore,

E_cell = E_SCE + E_j - (E^o_G - 0.059 log [H⁺])

where E_j is liquid-junction potential and E^o  is the standard electrode potential of the glass electrode.

In terms of pH,

or E_cell = E* + 0.059 log [H⁺]

E_cell = E* - 0.059 pH

Thus, cell potential is directly proportional to pH i.e. :

Ecell ∝ µ pH

where E* includes the standard electrode potential of glass electrode, potential of reference electrode and liquid-junction potentials between the reference electrode and solution. Beside these three potentials there is the other potential known as the asymmetry potential that is also contributing to this. Asymmetry potential is a little potential that exists across the membrane, even while the inner reference solution and the test solution are identical. A source of asymmetric is not much clear. It might be because of the degree of hydration of the inner and outer surface of the glass membrane or because of its structural design or because of mechanical and chemical attack whilst in use. The degree of hydration of outer surface will also modify if the electrode is permitted to dry out for a few time. Because of this it is advised in which the electrode should be stored either in water or in damp cotton wool. It is not probable to determine the value of asymmetry potential, thus, it is essential to calibrate glass membrane electrode along with suitable buffer solutions. As the value of the asymmetry potential could change along with electrode use, it is essential to carry out calibration at least daily.