Ion exchange chromatography resin nomenclature
In Cation-Exchange Chromatography, positively charged proteins (cations) are attracted to the negatively charged solid media (buffer cations originally balancing negative charges on the solid media are “exchanged” by protein cations).
In Anion-Exchange Chromatography, negatively charged proteins (anions) are attracted to the positively charged solid media (buffer anions originally balancing positive charges on the solid media are “exchanged” by protein anions).
|Ion exchange chromatography resin type:||Cation Exchanger||Anion Exchanger|
|Functional groups of ion exchanger are charged:||Negatively||Positively|
|Protein's of interest net charge:||Positive (protein is a cation)||Negative (protein is an anion)|
|Advised buffer pH:||< pI - 1||> pI + 1|
|Resulting pH in the vicinity of solid phase (Donnan effect):||Up to 1 unit lower than buffer pH||Up to 1 unit higher than buffer pH|
Ion exchangers are usually additionally classified as “weak” or “strong.” The classification refers to the fact that functional groups on many ion-exchange absorbents maintain their charge only during a certain interval of pH. Functional groups on strong ion exchangers remain charged in wider pH windows than for weak ion exchangers. The weak/strong classification does not refer to the absorbent ability to bind proteins, it refers only to pKa value of their functional groups.