Affinity chromatography is a method of separating biochemical mixture based on a highly specific interaction between antigen and antibody, enzyme and substrate, receptor and ligand, or protein and nucleic acid. It is a type of chromatographic laboratory technique used for purifying biological molecules within a mixture by exploiting molecular properties, e.g. protein can be eluted by ligand solution. Biological macromolecules, such as enzymes and other proteins, interact with other molecules with high specificity through several different types of bonds and interaction. Such interactions include hydrogen bonding, ionic interaction, disulfide bridges, hydrophobic interaction, and more.The molecule of interest can be immobilized through covalent bonds. This occurs through an insoluble matrix such as chromatographic medium like cellulose or polyacrylamide. When the medium is bound to the protein of interest it becomes immobilized.