Latex-Agglomerated Anion Exchangers

A special type of pellicular anion exchangers was first introduced in 1975 by Small et al. [3] in their introductory paper on ion chromatography. These stationary phases, which are called latex-based anion exchangers, have been further developed by Dionex (Sunnyvale, CA, USA). The structure of these stationary phases is schematically depicted in Fig. 3-11. 

Manufacturer Toyo Soda Interaction Chemicals Sykam Shimadzu 

Type of column Polymethacrylate Polyvinyl resin Polymethacrylate Polymethacrylate 

Latex-based anion exchangers are comprised of a surface-sulfonated polystyrene/divi-nylbenzene substrate with particle diameters between 5 pm and 25 pm and fully animated porous polymer beads of high capacity, which are called latex particles. The latter have a much smaller diameter (about 0.1 pm) and are agglomerated to the surface by both electrostatic and van-der-Waals interactions. A scanning electron micrograph of this material is shown in Fig. 3-12. Hence, the stationary phase features three chemically distinct regions  

Although the latex polymer exhibits a very high exchange capacity due to its complete amination, the small size of the beads finally results in a low anion exchange capacity of about 0.03 mequiv/g. The pellicular structure of these anion exchangers is responsible for their high chromatographic efficiencies. The parameters 

Column ION-100 (ION-110) Metrosep Anion Supp 4 Metrosep Anion Supp 5  

Type of packing material Polyvinyl resin with Polyvinyl resin with Polyvinyl resin with 

The surface sulfonation of the substrate prevents the diffusion of inorganic species into the inner part of the stationary phase via Doiman exclusion (see Section 5.1). Therefore, the diffusion process is dominated by the functional groups bonded to the latex beads. The size of these beads determines the length of the diffusion paths, and thus the rate of the diffusion process [32]. 

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Review of different latex-agglomerated anion exchangers... 

In 1994, Lamb et al. developed a series of cryptand-based anion separators. The biggest advantage of cryptand columns, used in gradient elution mode, is the ability to elute non-polarizable and polarizable anions in the same run, which is very difficult (or even impossible) with latex-agglomerated anion exchangers and aminated grafted polymers. ... 

Latex cation exchangers were introduced by Dionex Corp. 10 years later than latex-agglomerated anion exchangers. These types of cation exchangers consist of a weakly sulfonated PS-DVB substrate with latex beads with a very small diameter agglomerated on its surface by both electrostatic and van der Waals interactions. 

Latex-agglomerated anion exchangers are chemically very stable. Even 4 mol/L sodium hydroxide is unable to cleave the ionic bond between the substrate particle and the latex beads. The selectivity is altered by changing the chemical... 

Review of Different Latex-Agglomerated Anion Exchangers... 

By agglomerating acrylate-based latex beads on polystyrene/divinylbenzene substrates, a separation of chlorate and nitrate can also be achieved, which was previously not possible using conventional ion exchangers. These two anions exhibit the same interactions with both latex-based anion exchangers and directly aminated substrates and, thus, co-elute at these stationary phases. Therefore, ion-pair chromatography was used for this separation, which allows baseline separation of chlorate and nitrate due to their... 

Like anion exchangers, cation exchangers are divided into polymer-based cation exchangers (PS-DVB, EVB-DVB, polymethacrylate, and polyvinyl copolymers), latex-agglomerated cation exchangers, silica-based, and other (e.g., crown ether, aluminia materials).Modern cation exchangers contain sulfonic, carboxylic, car-boxylic-phosphonic, and carboxylic-phosphonic-crown ether functional groups. 

Fig. 1. Simultaneous separation and detection of anions and cations on a latex agglomerate column. Column Dionex HPIC-CS5 cation exchange column (250X2 mm) with precolumn HPIC-CG5 (50 X 4 mm) eluent 0.5 mM copper sulfate, pH 5. 62 flow rate 0.5 ml/min sample volume 20 gl containing 0.1 m M of each ion detection two potentiomet-ric detectors equipped with different ion-selective electrodes in series. Peaks (1) chloroacetate, (2) chloride, (3) nitrite, (4) benzoate, (5) cyanate, (6) bromide, (7) nitrate, (8) sodium, (9) ammonium, (10) potassium, (11) rubidium, (12) cesium, (13) thallium. Reprinted with permission from [10].

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