Monolithic stationary phases organic polymer monoliths

Table 1.1 gives a comprehensive, albeit fragmentary, snmmary of investigated organic monolithic polymer systems (based on all different kinds of styrene, acrylate, methacrylate, (meth)acrylam-ide building blocks, as well as mixtnres thereof) together with their preparation conditions and ntilization as stationary phase. 

Svec, R, Organic polymer monoliths as stationary phases for capillary HRLC, Journal of Separation Science 27(17-18), 1419-1430, 2004. 

Li, Y., Chen, Y., Xiang, R., Ciuparu, D., Pfefferle, L. D., Horwath, C., and Wilkins, J. A., Incorporation of single-wall carbon nanotubes into an organic polymer monolithic stationary phase for mu-HPLC and capillary electrochromatography, Analytical Chemistry 77(5), 1398-1406, 2005. 

The molecular imprinting strategy can be applied for the recognition of different kinds of templates from small organic molecules to biomacromolecules as proteins. Some examples of separations investigated with MIP monoliths in CEC and LC are shown in Table 2. The influence of the imprinted monolithic phase preparation procedure and of the separation conditions on the selectivity and chromatographic efficiency have been widely studied [154, 157, 161, 166, 167, 192]. The performance of imprinted monoliths as chromatographic stationary phase has also been compared to that of the traditional bulk polymer packed column [149, 160]. It was shown that the monolithic phases yielded faster analyses and improved chiral separations. 

In recent years, the interest in using porous silica and polymer-based monolithic stationary-phase media for ion chromatographic separations of inorganic and organic ions has increased.As compared to particle bed columns, monolithic columns represent a single piece of porous cross-linked polymer or porous silica. Monoliths are made in different formats as porous rods, generated in thin capillaries or made as thin membrane or disks. 

Capillary electrochromatography has experienced rapid progress during the last decade, expanding from 17 publications in 1994 to 191 in 2007. This has also led to several books and reviews [93-104] and analytical instrumentation is readily commercially available [105]. The developments in CEC include research on optimum stationary phases (polymer or silica based, adsorbed or imprinted, etc.), mobile phases (aqueous electrolytes with/without admixture of organic solvents or pseudophases) and apparatus design (open-tubular, packed or monolithic capillaries) up to lab-on-a-chip devices for pTAS [107]. 

Organic polymers are synthesized within capillaries, with polystyrene-divinylbenzene (PS-DVB) and polymeric methacrylates as the most common stationary phases. The most common process to make capillary monoliths includes opening silanol groups on the fused silica walls with sodium hydroxide, attaching a wall linkage, polymerization with monomer, cross-linker, porogen, and initiator, and sometimes grafting with other functionalities. 

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