What is the difference between a strong ion exchanger and a weak ion exchanger? How do I know which one to choose for a particular application?
The terms “strong” and “weak” refer to the acid/base properties of the functional group. If the ligand is derived from a strong acid or a strong base it is referred to as a strong ion exchange resin. If the ligand is derived from a weak acid or a weak base it is referred to as a weak ion exchange resin. For example, Toyopearl SuperQ-650 resin (pKa about 12.2) is functionalized with a quaternary amine which is considered a strong base. Hence it is called a strong anion exchange resin. However, Toyopearl DEAE-650 is functionalized with a putative weak basic group and is called a weak anion exchange resin. The pKa of Toyopearl DEAE-650 is approximately 11.5 which is quite high for a weak base and is therefore amenable to buffers much higher than other DEAE resins. The same is analogous for cation exchange media. In either case the interaction is based on ionic interactions and the strength of binding (unless very close to the pKa) is not considered strong or weak but is similar for any io
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