relative adsorption

If $Γ i σ$ and $Γ 1 σ$ are the Gibbs surface concentrations of components i and 1, respectively, with reference to the same, but arbitrarily chosen, Gibbs surface, then the relative adsorption of component i with respect to component 1, is defined as

$Γ i 1 = Γ i σ − Γ 1 σ c i α − c i β c 1 α − c 1 β$

and is invariant to the location of the Gibbs surface. Alternatively, $Γ i 1$ may be regarded as the Gibbs surface concentration of $i$ when the Gibbs surface is chosen so that $Γ i σ$ is zero, i.e. the Gibbs surface is chosen so that the reference system contains the same amount of component 1 as the real system. Hence $Γ 1 1 ≡ 0$ .

Source:

PAC, 1972, 31, 577 (Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry) on page 591