Strong anion-exchange sorbents

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

FIGURE 12 Plots of the approach distance a (in angstroms) versus k for the protein human serum albumin (HSA) (pi = 5.85, Mr = 69,000) measured with the strong anion exchange sorbent, Mono-Q, under conditions of varying NaCI concentration to achieve smaller kf values at a flow rate of I mL/min and at a temperature of 298 K with (I) 20 mM piperazine buffer, pH 9.6 (2) 20 mM triethanolamine, pH 7.5 (3) bistris buffer, pH 6.5 and (4), 20 mM piperazine buffer, pH 5.5, as the eluents. Data selected from Ref. 542. 

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... 

TABLE 7 Representative Zc and In K,ex Values for Several Polypeptides and Proteins Analyzed with the Strong Anion Exchange HP - IEX Sorbent, Mono-Q, Fractogel-TMAE, and LiChrospher 1000 TMAE... 

The choice of the sorbent is dictated by the characteristics of both the analytes and their potential interferences. The sorbents most frequently employed here are silica, alkylsilane-modified silica (bonded phases), alumina, porous polymers (with and without ion-exchange groups) and carbon-based materials. One typical application is a method for the determination of hexavalent chromium in soils [10] using the on-line system depicted in Fig. 4.9. After USAL, the analytes in the leachate were directly determined or preconcentrated depending on their concentration. Concentration was performed by on-line solid-phase extraction using a laboratory-made minicolumn packed with a strong anion-exchange resin. The absolute limits of detection were 4.52 and 1.23 ng without and with preconcentration, respectively. 

Additives to diet cola—caffeine, saccharin, and sodium benzoate—represent several different classes of compounds that may be extracted on anion-exchange sorbents simultaneously. Caffeine and saccharin are neutral compounds and sodium benzoate is an organic anion (Fig. 6.14). Caffeine and saccharin sorb by van der Waals interaction on the silica-bonded ion-exchange sorbent and the sodium benzoate by anion exchange. The sorbent chosen is a strong anion exchange in chloride form. The sorbent is first cleaned and... 

The high affinity of Pd-chloro-complexes to strong anion exchange materials enables the use of various anion exchange sorbents for preconcentration of Pd with simultaneous elimination of cationic interferents. Especially styrene or acrylic polymers cross-linked with divinylbenezene can be applied for enrichment of PGE from large sample volumes (Matsubara et al. 2000 Kovacheva and Djingova 2002 Lesniewska et al. 2006). 

A single multiresidue method was developed to determine 109 priority compoimds listed in the 76/464/EEC Coimcil Directive on Pollution of the EU [49]. For trapping analytes, automated off-line SPE with a polymeric sorbent "Oasis" 60 mg cartridge, was optimized. A multianalyte method for the confirmation and quantitation of 16 selected sulfonylurea, imidazolinone, and sulfonamide herbicides in surface water has been proposed [50]. This method is based on analyte extraction with a polymeric material (RP-102) and extract cleanup with a strong anion exchanger (SAX) cartridge stacked on... 

A cleanup step on sohd-phase extraction (SPE) cartridges is often employed to remove interfering compounds co-extracted with folates from the real matrix. The most used stationary phases include strong anion-exchange (SAX) materials and affinity chromatographic sorbents with immobilized folate-binding protein. Both provide high recoveries, but only the affinity column purifies and concentrates the extracts efficiently. 

Tbe strong-base nature of functional groups of fibrous anion exchangers permits their use as universal sorbents for a great number of gaseous toxic impurities. It is also reasonable to use SBF for purification of wastewaters. 

Thus it follows from the studies performed that the strong-base fibrous anion exchangers are efficient sorbents of sulphur dioxide in the gas phase and can be used in sanitary air purification. 

Mixed-mode sorbents contain both nonpolar and strong ion (cation and/or anion) exchange functional groups, targeted for the extraction of basic drugs. 

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