Ion Exchange Chromatography

Ion Exchange Chromatography 

Ion Exchange Chromatography (IEC or IEX) is driven by interactions between charged target molecules and charged immobilized ligands on the chromatography resin. IEX can be divided into two different sub types. Cation exchange chromatography, in which positively charged species in the mobile phase bind to a negatively charged ligand on the resin; and anion exchange chromatography, in which the binding species in the mobile phase are negatively charged, and the immobilized ligand is positively charged. 

After the molecule of interest has been adsorbed, the column is washed to remove any residual unbound species from the solid phase. The bound molecules are then desorbed using a gradient of a second, higher ionic strength mobile phase to steadily increase the ionic strength of the eluent solution. An alternative desorption method involves using a mobile phase of greater or lesser pH than the equilibration mobile phase to give your molecule of interest or the ligand a charge at which they will not interact and your molecule of interest elutes from the resin.

Applications

Ion Exchange Chromatography is the most widely used chromatographic mode in biopurification and applied in most downstream processing platforms. The typical scheme in IEX of binding the target, washing the column and eluting the target is called ’bind/elute mode’ and is often applied in intermediate purification steps for example in downstream processing of antibodies. Anion Exchange Chromatography is an integral part of most plasma protein purification platforms, such as Factor VIII purification.

In other cases it may be more advantageous to select conditions at which the target molecule will pass through the column unbound while the impurities will bind. This mode of binding is often referred to as "flow through mode" and it is most typically used with anion exchangers to remove DNA, endotoxins, and other negatively charged species while letting your target molecule to flow through the column. 

TOYOPEARL and TSKgel IEC Resins

Tosoh Bioscience provides a broad range of strong and weak ion exchangers for anion and cation exchange chromatogaraphy. The terms “strong” and “weak” refer to the acid/base properties of the functional group. A strong ion exchange resin will have the same charge density on its surface over a broad pH range, whereas the charge density of a weak ion exchanger changes with pH. The selectivity and the capacity of a weak ion exchanger are different at different pH values.

The type of ion exchange resin that will work best for a particular process will depend on the variance in the ionization state of the functional groups at different pH values. When developing a purification process, it is usually recommended that the chromatographer begin with a strong ion exchanger (e.g., quaternary amine, sulfonic acid, or sulfopropyl), and then to try a weak ion exchanger (e.g., DEAE or carboxymethyl) if the selectivity is unsatisfactory.

TOYOPEARL ion exchange resins are functionalized versions of the TOYOPEARL HW size exclusion resins and are therefore based on hydroxylated polymethacrylic polymer beads. The TSKgel IEC resins use the same methacrylic polymer chemistry as the TOYOPEARL resins but have a higher degree of crosslinking, making for a more rigid bead.

The TOYOPEARL GigaCap series of high capacity ion exchange resins provides a broad range of weak and strong anion and cation exchange resins for a variety of applications.