Anion nanobead-agglomerated

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.

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. 

Table 3.7 Structural and technical properties of hydroxide-selective, nanobead-agglomerated anion...

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. 

The introduction of the nanobead-agglomerated lonPac ASS many years ago significantly facilitated the analysis of polarizable anions. The hydrophobicity of the functional groups bonded to the nanobeads was lowered, so that polarizable anions could be eluted with a standard carbonate/bicarbonate eluent. To minimize adsorption effects, some / -cyanophenol was added to this eluent. The influence of / -cyanophenol on the peak shape is illustrated in Figure 3.55 (see Section 3.4.1.4). Due to the compatibility of this eluent with commercial membrane suppressors and the subsequent decrease in dead volume, peak broadening was significantly reduced. 

Endothall can be analyzed together with common inorganic anions under standard chromatographic conditions on nanobead-agglomerated anion exchangers. It typically elutes between nitrate and orthophosphate. 

Arogenic acid is not stable at acidic pH. Thus, it cannot be analyzed by cation-exchange chromatography. However, on a nanobead-agglomerated anion exchanger with alkaline eluents, the separation of this compound from the amino acids phenylalanine and tyrosine is accomplished without any problem. 

---