Basic facts about ion-exchange resin
Ion-exchange resin is resin that exchanges ions by seizing the ions in water and releasing its own ions in exchange.
*Pure water: Pure (deionized) water is tap water or another form of water from which cations such as sodium, calcium, and magnesium and anions such as chlorine and carbonic acid have been removed. It is used in various industries for its characteristic of not containing minerals or chlorine.
Basic elements of “separation” using ion-exchange resin
The basis for separation using ion-exchange resin is (I) ion exchange. Ion exchange (adsorption) is different from physical adsorption. In an ion-exchange reaction, ions already adsorbed into ion-exchange resin are replaced with substances for the resin to adsorb (target substances and non-target substances). In exchange for the new substances adsorbed, the originally adsorbed ions are released. Ion exchange is an equilibrium reaction between the exchange group and the substance to be adsorbed, and between that substance and the substance already adsorbed.
(I)Ion exchange
Resin is selected so that either the target substance, the non-target substance, or both substances enter (diffuse through) the resin.
- I-1 The target substance is adsorbed into the ion-exchange resin, separating from the non-target substance that is not adsorbed.
- I-2 The non-target substance is adsorbed into the ion-exchange resin, separating from the target substance that is not adsorbed.
- I-3 Both the target and non-target substances are adsorbed into the ion-exchange resin, and are separated into target and non-target when released from the resin by changing the type and concentration of the eluate.
Resin dipping with a solution containing the target → rinsing (target recovery I-2) → eluate (target recovery I-1, 3)
(II)Chromatographic separation
Chromatographic separation differs from ion exchange in that target and non-target ions are separated without being adsorbed into ion-exchange resin. When target and non-target ions pass through the resin layer, they are affected by various factors such as the ion exchange group in the ion-exchange resin and the structure of the matrix, and differences arise in the speed of passing through the resin layer. This difference is used to separate substances.
Resin dipping with a solution containing the target → dipping with developer → recovery of target (repeat continuously)
II-1 Size exclusion (gel filtration, size exclusion)
※ Selecting resin so that at least one of the target or the non-target, or both substances enter (diffuse through) the resin.
Sieving using the difference in molecular weight of the target and non-target substances.
II-2 Ion retardation
Ion retardation: For separating pairs of ionic substances
Ion exclusion
Includes separation of pairs of ionic substances and separation of an ionic substance and non-ionic substance.
※Selecting resin so that both the target and the non-target enter (diffuse through) the resin.
Uses differences in repulsion of the exchange group to the target and non-target substances.
The substance receiving the strongest repulsion effect comes out of the resin layer first.
II-3 Affinity
Selecting so that at least the target substance enters (diffuses through) the resin.
A substance with a high affinity for the target is adsorbed into the exchange group of the resin in advance so that the target stays or adsorbs longer than the non-target. The non-target is flushed out first, then the target is dissolved out or recovered by driving it out with developer. (For adsorption, the “ionic adsorption” method is used; to create a long retention period, the “chromatographic separation” method is used.)
