Anion exchanger latexed

FIGURE I Schematic diagram illustrating the construction of an anion exchange latex coated, surface-sulfonated, nonporous cross-linked polyethylvinylbenzene-divinylbenzene resin bead. 

Menger et al. (33) also reported a similar polymeric library to identify catalysts for the hydrolysis of a phosphate ester (102), where a 30,000-fold increase versus the uncatalyzed reaction rate was obtained. Miller and Ford (103) reported the synthesis of a 32-member discrete polymer library based on anion-exchange latexes and its screening for the alkaline hydrolysis of p-nitrophenylalkane carboxylates. The reported efforts may represent just the tip of an iceberg in terms of opportunities granted by polymeric catalysts, and an expansion of knowledge derived from further efforts is to be expected in the near future. 

Polymer-supported catalysts often have lower activities than the soluble catalysts because of the intraparticle diffusion resistance. In this case the immobilization of the complexes on colloidal polymers can increase the catalytic activity. Catalysts bound to polymer latexes were used in oxidation reactions, such as the Cu-catalyzed oxidation of ascorbic acid,12 the Co-catalyzed oxidation of tetralin,13 and the CoPc-catalyzed oxidation of butylphenol14 and thiols.1516 Mn(III)-porphyrin bound to colloidal anion exchange resin was... 

A unique anion-exchange column has been developed that has a thin (non-diffusion limited) anion-exchange phase coated onto a 10-/nm latex bead. When a mobile phase of 0.15 M NaOH is used, neutral carbohydrates are converted into anions, which are separated on the column. Although the resin has low capacity, and probably causes degradation of the carbohydrates, when it is coupled to a triple-pulsed, amperometric detector, the system provides extremely sensitive, high-resolution separations. 

Pellicular packings may also consist of a fully functionalized layer encapsulating solid particles, where there is no physical attachment of the active layer to the core particles [7] or as colloidal particles bearing charged moieties (latex) electrostatically bound to a solid core functionalized with groups of opposite charge [8] (Fig. 1). Most of the anion-exchange columns in use today for either carbohydrate or ion chro-... 

The highly cross-linked polymeric nonporous core may consist of either a polystyrene-divinylbenzene or an ethylvinylbenzene-divinylbenzene substrate. The latex coatings are generally made from vinylben-zenylchloride polymer cross linked with divinylbenzene and fully functionalized with an appropriate quaternary amine for introducing anion-exchange properties. 

Pellicular anion-exchange sorbents may also consist of quaternized latex hydrophobically coated onto the surface of an unsulfonated polystyrene solid core. However, using hydro-organic mobile phases can easily wash off the latex particles held onto the particle surface by hydrophobic interactions. 

Organic polymers are functionalized directly at their surface, with the exception of latex-based anion exchangers (see Section 3.3.1.2), where the totally porous latex particle acts as ion-exchange material. Surface-functionalized, pellicular substrates show a much higher chromatographic efficiency compared to the fully functionalized resins. The organic polymers mentioned above are functionalized in a two-step process ... 

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. 

Fig. 3-11. Structure of a latex-based anion exchange resin.

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 ... 

An outer layer of latex beads, which carry the actual anion exchange groups,... 

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... 

Review of different latex-agglomerated anion exchangers... 

Both separator columns have in common a relatively low loading capacity resulting from the high degree of crosslinking of the substrate particles. The functionality of the latex beads corresponds to that of a conventional anion exchanger, for example, the AS3 column. 

Compared to conventional anion exchangers such as the AS4A column, the acrylate-based latex polymer of a Fast-Sep column exhibits a lower pH stability. However, longterm experiments with the Fast-Sep column showed no deterioration as long as the pH value of the mobile phase was kept between 2 and 11. The pH value of the sample to be analyzed should not exceed 13. 

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... 

Fig. 3-21. Elution profile of the IonPac AS9 latex anion exchanger. - Eluent 0.00075 mol/L NaHC03 + 0.002 mol/L Na2C03 flow rate 1 mL/min detection suppressed conductivity injection volume 50 pL solute concentrations 1 ppm fluoride, 5 ppm chlorite, 1.5 ppm chloride, 6 ppm nitrite, 10 ppm bromide, 15 ppm chlorate and nitrate, 20 ppm orthophosphate and sulfite, and 25 ppm sulfate.

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