Every molecule, particularly proteins, have a complex three dimensional structure. Ligands that have the ability to recognize one of the structural motifs of a molecule are used in what is called affinity chromatography. This interaction can be extremely specific and the ligand will interact with only one type of molecule, or the ligand can be designed so that it recognizes a group of structurally similar molecules.

Ideally the ligand on the solid support should have excellent avidity to the target molecule. However, it is possible to have too much of a good thing. If the adsorption is too strong it will make it too difficult to desorb the target from the column.

If the affinity ligand is a peptide or protein, special care must be taken so that its structure is not destroyed. 

Despite the difficulties in developing an affinity chromatography resin, these resins are very powerful in isolating molecules from a very complex feedstream.