Self-assembly in two binary mixtures based on three isomeric oligopyridines at the liquid/HOPG (highly oriented pyrolytic graphite) interface is presented. Despite their structural similarity the molecules display exclusive phase separation, which is attributed to the highly specific intermolecular hydrogen bonding interactions. Variation of the mole fractions in solution reveal strongly preferred adsorption of the major compound, which underlines the importance of self-recognition for self-assembly. Those findings at the molecular level can be applied to separation issues on a macroscopic scale, leading to a completely new concept of separation, which could have a strong impact on various chromatographic processes. Binary SAMs put to work: Binary mixtures of structurally closely related isomeric oligopyridine molecules show exclusive phase separation in two-dimensional self-assembly at the solid/liquid interface (see figure). The presence of only a slight imbalance of the oligopyridines in the supernatant causes the adsorption of only one isomer, in a process driven by the energy penalty of the hetero phase boundaries. Such S-shape behaviour can be exploited for separation purposes.