Kits and columns for ion exchange chromatography
Ion exchange chromatography (IEX) separates proteins depending on their net surface charge, through electrostatic interactions that occur between proteins and a stationary charged phase. Two types of IEX exist:
- Anion exchange (positively charged stationary phase which binds to negatively charged proteins)
- Cation exchange (Negatively charged stationary phase which binds to positively charged proteins)
Ion exchange chromatography is commonly used as an intermediate step in a protein purification method, but it can give high resolution for some proteins when used earlier or later during purification.
All proteins have a net charge which depends on the amino acid composition of the protein as well as covalently attached modifications. The net charge of a protein is influenced by the pH of the solvent in which it is dissolved, as the solvent exchanges hydrogen ions with the proteins. The isoelectric point (pI) of a protein is the pH at which the protein has no net charge. At pH above pH, a protein will have a net negative charge, while a pH below the pH will lead to a net positive charge. Thus, the pH of the solvent can be adjusted to facilitate binding to IEX or promote elution of a bound protein.