Ion exchange is a common unit operation in pretreatment. What is ion exchange?
Ion exchange is the interaction between ionic functional groups in a compound and oppositely charged functional groups on the adsorbent surface. Ion exchange can be controlled by conditions such as solvent pH, ionic strength, and selectivity of competing ions. According to the size of the interaction energy between the compound and the adsorbent, the ion exchange effect is strong or weak.
In solid phase extraction (SPE), the ion exchange effect must also be divided into strong and weak, there are SCX (Strong Cation Exchange) strong cation exchange solid phase extraction column, SAX (Strong Anion Exchange) strong anion exchange solid phase extraction column, There are four types of WCX (Weak Cation Exchange) weak cation exchange solid phase extraction columns and WAX (Weak Anion-Exchange) weak anion exchange solid phase extraction columns.
So how to choose and distinguish these four different ion exchange solid phase extraction cartridges?
The cation exchange solid phase extraction cartridge can dissociate the anion groups, adsorb the cations in the solution, can be used for the ionization of basic substances, and can retain basic compounds, while the strong cation exchange column can retain weak basic compounds.
Welchrom® SCX strong cation exchange column, the packing group is benzenesulfonic acid group, the sulfonic acid group is negatively charged after activation, and the basic target is positively charged. During dehydration, ammoniated organic reagents are generally used, and the sulfonic acid group is neutralized by ammonia ions. At this time, the basic target substance is eluted together with the organic phase. Generally, it can be used in aqueous samples, biological fluids and alkaline in the organic phase. Purification of Compounds.
Welchrom® WCX weak cation exchange column, the packing group is generally carboxyl group, so the effect of anion exchange is not too strong, so it is not necessary to use a strong basic elution solvent to elute the target compound. Compared with the detection range of pH 0-14 for strong cations, the pH range of weak cations is relatively narrow, which can generally be applied to the detection of alkaloids, nitrogen heterocycles and other compounds.
Anion exchange solid phase extraction cartridges can dissociate cationic groups, adsorb anions in solution, can be used for ionization of acidic substances, and can retain acidic compounds, while strong anion exchange columns can retain weakly acidic compounds.
Welchrom® WCX strong anion exchange column is a quaternary ammonium salt functional group bonded on the surface of silica gel, which is mainly used for the adsorption and enrichment of weak anion target compounds, such as organic acids, etc. It can be mainly used to enrich negatively charged targets from water or non-water For example, purification of basic compounds in aqueous samples, biological fluids and organic phases.
Welchrom® PSA weak anion exchange column has an ethylenediamine functional group. It is a similar adsorbent to NH2, but has a stronger ion exchange capacity than NH2. It can be used to separate structural isomers and lipid samples. The extraction of compounds with polar groups can also be used to remove polar compounds (such as carbohydrates, pigments), organic acids, phenols, etc. in the extract in pesticide residue analysis.
|Strong cation exchange column
|Weak cation exchange column
|Strong anion exchange column
|Weak anion exchange column