Network polymeric stationary phases

A variation of these types of chiral stationary phases was reported by Anderson et al. [42], who synthesized a series of network polymeric stationary phase based on para-substituted AA -dialkyl-L-tartaramide dibenzoates. 

The analysis demonstrates the elegant use of a very specific type of column packing. As a result, there is no sample preparation, so after the serum has been filtered or centrifuged, which is a precautionary measure to protect the apparatus, 10 p.1 of serum is injected directly on to the column. The separation obtained is shown in figure 13. The stationary phase, as described by Supelco, was a silica based material with a polymeric surface containing dispersive areas surrounded by a polar network. Small molecules can penetrate the polar network and interact with the dispersive areas and be retained, whereas the larger molecules, such as proteins, cannot reach the interactive surface and are thus rapidly eluted from the column. The chemical nature of the material is not clear, but it can be assumed that the dispersive surface where interaction with the small molecules can take place probably contains hydrocarbon chains like a reversed phase. 

Porous organic polymers (Figure 10) are potential electrochromatographic stationary phases for the analysis of pharmaceuticals. The polymer network is generally formed inside the capillary by a stepwise chain polymerization reaction. Polymerization reaction mixtures usually consist of a combination of monomers and cross-linker, initiator, and a porogenic mixture of solvents. 

A third type of synthetic polymer-based chiral stationary phase, developed hy Blaschke. is produced when a chiral selecior is either incorporated within the polymer network or attached as pendant groups onto the polymer matrix. Both arc analogous to methods used lo produce polymeric chiral stationary phases for gc. 

S. Anderson, S. Allenmark, P. Moller, B. Persson, and D. Sanchez, Chromatographic separation of enantiomers on V,V -diallyl-L-tartardiamide-based network—Polymeric chiral stationary phases, J. Chromatogr. 741 (1996), 23. 

In the case of diffusion of a substance through a stationary solid or semisolid phase such as the polymeric network of a membrane, it is convenient to view the stationary phase as a fixed reference and to consider only the flux of mobile molecules, namely dmg or external solvent. Assuming that the diffusion processes do not imply important variations of membrane density [50] and that no convective flux is present (this is the most common situation met in practice when dealing with membranes),... 

Instead of packed columns, monolithic (continuous bed), analytical, or capillary columns in the form of a rod with flow-through pores offer high porosity and improved permeability. Silica-based monolithic columns are generally prepared by gelation of a silica sol to a continuous sol-gel network, onto which a Cjg or another stationary phase is subsequently chemically bonded. Such columns provide comparable efficiency and sample capacity as conventional columns packed with 5-pm particle materials, but have three to five times lower flow resistance, thereby allowing higher flow rates and fast HPLC analyses. Rigid polyacrylamide, polyacrylate, polymethacrylate, or polystyrene monolithic columns are prepared by in sim polymerization. 

The most convenient and most popular analytical methodology to assess enantiomer purity is the direct separation of enantiomers on so-called chiral stationary phases (CSPs). CSPs consist of an (ideally) inert chromatographic support matrix incorporating chemically or physically immobilized SO species. CSPs may be created by a variety of SO immobilization techniques, including (i) covalent attachment onto fhe surface of suitably pre-functionalized carrier materials, (ii) physical fixation employing coating techniques, and (iii) incorporation into polymeric networks by copolymerization, or combinations of these procedures. 

More recently, columns have been developed where the stationary phase is formed of a porous polymer network inside the capillary. These are called monolithic phases, and have emerged as an alternative to traditional packed bed columns for use in micro-HPLC. They hold many advantages over traditional packed bed columns, being easy to manufacture since the monolith is formed in situ, often via a one-step reaction process, and its properties such as porosity, surface area, and functionality can be tailored. Another major advantage is that they eliminate the need for retaining frits. These columns can be manufactured from a variety of materials, but the most common include sol-gel, methacrylate-based, acrylamide-based, and styrene-based polymeric structures. 

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