Ions which possess a chemical affinity for the surface in addition to the
Coulomb interaction, where chemical is a collective adjective, embracing all interactions
other than purely Coulombic. Examples are van der Waals or hydrophobic bonding, pi-electron
exchange and complex formation. Specifically adsorbing ions can adsorb on an initially
uncharged surface and hence provide it with a charge. The term specifically adsorbed
applies to the sorption of all other ions having an affinity to the surface in addition
to the purely Coulombic contribution.
Source:
PAC, 1991, 63, 895
(Nomenclature, symbols, definitions and measurements for electrified interfaces in
aqueous dispersions of solids (Recommendations 1991))
on page 899