Those species which by virtue of their electron distribution between the solid and
liquid phase (or by their equilibrium with electrons in the solid) determine the difference
in Galvani potential between these phases. This definition requires that adsorbed
p.d. ions are part of the
adsorbent and belong to the category of
surface ions.
Source:
PAC, 1991, 63, 895
(Nomenclature, symbols, definitions and measurements for electrified interfaces in
aqueous dispersions of solids (Recommendations 1991))
on page 897