If ${\mathit{\Gamma }}_i^{\sigma }$ and ${\mathit{\Gamma }}_1^{\sigma }$ 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 $${\mathit{\Gamma }}_i^{\left(1\right)}={\mathit{\Gamma }}_i^{\sigma }-{\mathit{\Gamma }}_1^{\sigma }\frac{c_i^{\alpha }-c_i^{\beta }}{c_1^{\alpha }-c_1^{\beta }}$$ and is invariant to the location of the Gibbs surface. Alternatively, ${\mathit{\Gamma }}_i^{\left(1\right)}$ may be regarded as the Gibbs surface concentration of $i$ when the Gibbs surface is chosen so that ${\mathit{\Gamma }}_i^{\sigma }$ 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 ${\mathit{\Gamma }}_1^{\left(1\right)}\equiv 0$.