Ion Exchange Chromatography

Ion exchange chromatography separates molecules based on differences between the overall charge of the proteins. It is usually used for protein purification but may be used for purification of oligonucleotides, peptides, or other charged molecules. For interaction to occur, the protein of interest must have a charge opposite to that of the functional group of the sorbent particle. For example, immunoglobulins, which generally have a net positive charge, will bind to cation exchangers because they possess negatively-charged functional groups. Because the interactions are ionic, binding must take place under low ionic strength conditions. Elution is achieved by increasing the ionic strength of the mobile phase to reduce ionic attractions, or by changing the pH of the mobile phase to alter the ionization state of the protein.