Cation exchange silica-based materials

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. 

Traditionally, low crosslinked porous polymers modified by sulfonic or carboxylic acid groups (quaternary amines for the separation of cations) were the most widely used stationary phases. In recent years, silica-based chemically bonded or surface-modified (e.g. alumina treated) ion exchangers have found increasing use [159,484-488]. The trend towards increased use of modern porous polymer and silica-based materials is due to their higher performance and greater dimensional stability with different mobile phase compositions. 

In fact, every silica-based reversed phase represents a mixed-mode column, because besides the alkyl chains it has silanol groups, which are groups capable of weak cation exchange. Some C18 materials of the first generation, such as Partisil ODS from Whatman or Spherisorb ODSl from Waters, have only a very low carbon content (<5%) and a high number of free silanol groups. With these... 

The application of polymer monoliths in 2D separations, however, is very attractive in that polymer-based packing materials can provide a high performance, chemically stable stationary phase, and better recovery of biological molecules, namely proteins and peptides, even in comparison with C18 phases on silica particles with wide mesopores (Tanaka et al., 1990). Microchip fabrication for 2D HPLC has been disclosed in a recent patent, based on polymer monoliths (Corso et al., 2003). This separation system consists of stacked separation blocks, namely, the first block for ion exchange (strong cation exchange) and the second block for reversed-phase separation. This layered separation chip device also contains an electrospray interface microfabricated on chip (a polymer monolith/... 

Silica-based restricted access materials (RAM) have been developed for cleanup in bioanalysis, first for low molecular weight compounds in biofluids (Rbeida et al., 2005) and subsequently for biopolymers such as peptides (Wagner et al., 2002). A classification of different types of RAM has been given by Boos and Rudolphi (1997). Novel RAMs with strong cation-exchange functionality have been synthesized and implemented in the sample cleanup of biofluids. Racaityte et al. (2000) have shown that this type of RAM is highly suitable for the online extraction and analysis of... 

The first reversed-phase SPE sorbents were based on silica gel particles, similar to the particles used in HPLC. A number of phases are available ranging from C8 to C18 to anion- and cation-exchange functionalities. Recent advances in particle technology have included polymeric materials that combine the benefits of a water-wettable particle to retain polar analytes with a reversed-phase, hydrophobic moiety to... 

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