Strong cation-exchange sorbents

Figure 2.28. Interactions between analytes and ion-exchange sorbents (a) strong cation-exchange sorbent and (b) strong anion-exchange sorbent.

For example, strong cation-exchange sorbents based on silica consist of either an aromatic sulfonic acid or a propane sulfonic acid that is bonded to the silica matrix. These sorbents typically are available in their hydrogen form and have different exchange capacities. The aromatic exchangers have approximately 1 meq/g, while the propane sulfonic acids have much less, about 0.3 meq/g. The strong cation-exchange sorbents are available in both endcapped... 

Figure 6.3. Strong cation-exchange sorbent with trifunctional bonded phase.

Strong cation-exchange sorbent. This approach would be used for organic cations and combined with a methanol eluate (50 50 methanol/water) to help prevent sorption to the matrix of the sorbent by van der Waals interactions and to assist elution. Also the pH can be adjusted in the elution solvent such that the organic cation will loose its charge that is, the pH should be two pH units above the pA. Sodium hydroxide or potassium hydroxide may be used here to raise the pH in combination with the methanol (0.1 A). Organic compounds that contain nitrogen (amines) work well by this mechanism. 

Sorbent 500 mg of strong cation exchange sorbent in form. Condition the sorbent with 3 mL methanol and 3 mL of DI water. 

Figure 18 Analytical Profiles of Several Synthetic Peptides Separated on the Strong Cation-Exchange Mono S Sorbent[3471a b...

Anion-exchange sorbents for SPE contain weakly basic functional groups such as primary or secondary amines which are charged under low-pH conditions or strongly basic quaternary ammonium groups which are charged at all pHs. Cation-exchange sorbents for SPE contain weakly acidic functional... 

Figure 2.32. Example of a mixed-mode sorbent consisting of silica modified with octyl (C8) alkyl chains and strong cation-exchange sites bonded on the same sorbent particle.

The formula of an ion-exchange sorbent may be viewed as a chemical equation when a salt solution is introduced into the sorbent. For example, the sul-fonic-acid hydrogen form of the strong cation exchanger will exchange ion for K, if a KCl solution is introduced into the sorbent ... 

Elution of the ion-exchange sorbent may be carried out by several strategies. First, if the sorbent is a cation-exchange sorbent, the cations may be displaced with the of a strong acid (i.e., 20% solution of HNO3). This eluent will work well for metal cations. Another approach is to elute the cations with a more strongly held cation (Table 6.2) thus, sodium could be displaced by potassium on a... 

The extraction of methylimidazole from food is based on the cation exchange of the analyte onto the sorbent (Fig. 6.15). The food sample is prepared by homogenizing in methanol, filtering the sample, and evaporating the filtrate to dryness. The extract is reconstituted in water and filtered. The sample is now ready for application to the strong cation-exchange resin. 

For the purification of a library of amines generated by reductive amination, the use of strong cation-exchange adsorbents based on silica gel has been described [38]. An excess of aldehyde was used to ensure completion of the reaction and the crude reaction mixture was applied to a column of a strong cation-exchange adsorbent. The column was rinsed with methanol to remove the excess aldehyde and other neutral impurities while the basic products remained on the sorbent The adsorbent was then treated with 2 m anhydrous ammonia in methanol to elute the basic products in high purities. 

Conditioned an SPE column (strong cation exchange, 0.5-1.5 g sorbent,... 

S, Q, IP, N Chicken muscle QuEChERS liquid extraction with 1% (v/v) acetic acid/ACN and sodium sulfate, followed by d-SPE clean-up with a Bondesil-NH2 sorbent (plus additional strong cation exchange clean-np with Bond Elnt SCX cartridges for NMZs) 15... 

The most widely used sorbents with their characteristics are presented in Table 4. Mixed-mode columns containing mixtures of nonpolar (Cg, Cig, C4, etc.) and strong anion or/and strong cation exchange functional groups are available for applications for both acidic and basic compounds. These columns are designed to capitalize on multiple interactions of the analyte or different types of interactions from more than one type of analyte. Mixed-mode columns allow the development of more robust procedures, which are less dependent on the matrix, making cleaner extracts possible. 

---