Affinity chromatography can be used to purify and concentrate a substance from a mixture into a buffering solution, reduce the amount of unwanted substances in a mixture, identify the biological compounds binding to a particular substance, purify and concentrate an enzyme solution. 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.