Nanobead anion exchanger

With the exception of nanobead-agglomerated anion exchangers (see Section 3.4.1.4), where totally porous nanobeads act as ion-exchange material, organic polymers are functionalized directly at their surface. Surface-functionalized, the so-called pellicular substrates, show a much higher chromatographic efficiency than fully functionalized resins. 

Carbonate/Bicarbonate-Selective Grafted Polymers The most common surface-functionalized, carbonate/bicarbonate-selective grafted polymer is available under the trade name Dionex lonPac AS14. This universal anion exchanger for the analysis of inorganic anions was developed as an advanced successor product of the nanobead-agglomerated lonPac AS12A [23] (see Section 3.4.1.4). 

Nanobead-agglomerated anion exchangers are comprised of a surface-sulfonated poly(styrene-co-divinylbenzene) substrate with particle diameters between 5 and 10 pm and fully aminated, high-capacity porous polymer beads made of polyvinylbenzyl chloride or polymethacrylate, which are called nanobeads. The latter have a much smaller diameter (about 0.1 pm) and are... 

Figure 3.27 Structure of a nanobead-agglomerated anion-exchange resin.

An outer layer of nanobeads that carry the quaternary ammonium groups as anion-exchange functions... 

Carbonate-Selective Nanobead-Agglomerated Anion Exchangers At present. Thermo Fisher Scientific offers four different carbonate-selective, nanobead-agglomerated anion exchangers with diverse selectivities. The structural and technical characteristics of these separator coliunns are summarized in Table 3.6. Special columns for the separation of polyvalent anions and carbohydrates, amino acids, and oligonucleotides are also available. 

Table 3.6 Structural and technical properties of carbonate-selective nanobead-agglomerated anion exchangers.

When it was introduced, lonPac AS12A was clearly the most modern nanobead-agglomerated anion exchanger for the separation of fluoride, oxyhalides, and mineral acids. The latest development in the field of universal purpose anion exchangers for water analysis is lonPac AS22. It is based on a hyper-branched polymer and discussed in Section 3.4.I.5. 

Anion-exchange stationary phases described in Section 3.4.1.4 are based on colloidal anion-exchange particles (the so-called nanobeads or latex particles) that are electrostatically bound to the surface of nonporous surface-sulfonated or sur-face-carboxylated PS/DVB and EVB/DVB copolymer beads. This approach to stationary-phase design provides a number of advantages including the following ... 

A much higher resolution between fluoride and chloride is obtained by using a CarboPac PAl-type stationary phase. Compared to nanobead-agglomerated anion exchangers such as lonPac AS4A-SC, this separator column, which was initially developed for the analysis of carbohydrates, exhibits a signiflcantly higher capacity. As a result, chloride retention increases to more than 20 min. 

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