Methacrylate-based monolithic columns

Buszewski, B., Szumski, M., and Sus, S. (2002). Methacrylate-based monolithic columns for micro-HPLC and CEC. LC-GC Europe 15, 792-798. 

Ye et al. found a parallel between CE and CEC, in dynamically modified capillary separations [52], A column packed with bare silica was dynamically modified with cetyltrimethylaammoinium bromide (CTAB), a long-chain quaternary ammonium salt that was adsorbed onto the silica surface and produced a hydrophobic layer. The same additive, but with a completely different effect, was used Wu et al. [53]. They employed a methacrylate-based monolithic column and added in the mobile phase CTAB or sodium dodecyl sulfate (SDS) to generated EOF. Ten analytes, ranging from acidic to basic, were separated in both cases. 

Xie, S., Svec, F., and Frechet, J.M.J., Rigid porous polyacrylamide-based monolithic columns containing butyl methacrylate as a separation medium for the rapid hydrophobic interaction chromatography of proteins,. Chromatogr. A, 775, 65, 1997. 

It is of much interest to compare polymer monoliths with monolithic silica columns for practical purposes of column selection. Methacrylate-based polymer monoliths have been evaluated extensively in comparison with silica monoliths (Moravcova et al., 2004). The methacrylate-based capillary columns were prepared from butyl methacrylate, ethylene dimethacrylate, in a porogenic mixture of water, 1-propanol, and 1,4-butanediol, and compared with commercial silica particulate and monolithic columns (Chromolith Performance). 

In a related study this group also demonstrated the use of non-volatile solvents in CEC-MS without compromising the quality of spectra that has also been demonstrated using polymer-based monolithic column prepared by in situ copolymerization of butyl methacrylate with sulfonic acid functionalities. 

Huang, H. Y., Chiu, C. W., Huang, I. Y., and Yeh, J. M. (2004). Analyses of preservatives by capillary electrochromatography using methacrylate ester-based monolithic columns. Electrophoresis 25, 3237-3246. 

Such precise control of porous properties is expected to be very useful in the design of specialized CEC columns for separation in modes other than reversed-phase. For example, size exclusion chromatography (SEC) is an isocratic separation method that relies on differences in the hydrodynamic volumes of the analytes. Because all solute-stationary phase interactions must be avoided in SEC, solvents such as pure tetrahydrofuran are often used as the mobile phase for the analysis of synthetic polymers, since they dissolve a wide range of structures and minimize interactions with the chromatographic medium. Despite the reported use of entirely non-aqueous eluents in both electrophoresis and CEC [65], no appreciable flow through the methacrylate-based monoliths was observed using pure tetrahydrofuran as the mobile phase. However, a mixture of 2% water and tetrahydrofuran was found to substan-... 

The concept of monolithic columns in the shape of disks was first introduced at the beginning of the 1990s by Tennikova, Belenkii, and Svec. They prepared hydro-phobic methacrylate-based monolithic disks with a diameter of 20 mm and a thickness of 1 mm which demonstrated a very efficient separation of a protein mixture. After this initial research, monolithic disks of different diameters and thicknesses were prepared and used for various chromatographic separations. The smallest monolith had a diameter of only 1.8 mm, while the largest had a diameter of 50 mm. The thickness was between 0.3 and 7 mm. In this way, the monolith volume differed by several orders of magnitude. The monolithic disks contained different chemical moieties which were used for separations in ion exchange, hydrophobic, and affinity interactions, as well as reversed phase modes. 

The concept of monohthic columns in the shape of disks was first introduced at the beginning of the 1990s by Tennikova, Belenkii, and Svec. They prepared hydrophobic methacrylate-based monolithic disks with a diameter of 20 mm and a thickness of 1 mm which... 

The preparation of methacrylate-based monoliths has been described in great detail by Vlakh and Tennikova [328] it is relatively straightforward. The column is filled with a polymerization mixture, sealed at both ends, and the polymerization is initiated by heat or UV radiation. The functional monomer in the polymerization mixture controls the polarity of the final monolithic material, while the cross-linking agent (a monomer with two or more double bonds) and the poro-gen solvent determine the size and the distribution of the pores. Polymerization is initiated by azo compounds such as 2,2 -azo-bis-isobutyronitrile (AIBN), which requires temperatures between 60 and 80 °C to decompose with the formation of free radicals. 

A boronate affinity monolithic column first appeared in 2006. Hilder and co-workers first prepared an epoxy-functionalized monolithic capillary through copolymerization of glycidyl methacrylate (GMA) and EDMA. The poly(GMA-co-EDMA) base monolithic column was then chemically modified through nucleophilic attack of the epoxide with p-hydroxyphenylboronic acid (Scheme 11.6). Since then, various boronate affinity monolithic columns have been rapidly developed because of the merits of both boronate affinity and monolith columns. Liu and co-workers has made many studies in recent They synthesized the hydrophilic bor-... 

CEC-DAD, methacrylate ester-based monolithic column, phosphate buffer MeCN at pH 3 as eluent... 

Table 7.1 shows the pore properties of several polymer monolithic columns prepared from styrene/DVB, methacrylates, and acrylamides along with the feed porosity and column efficiency, summarized from several recent publications. Some important points seem to be clearly shown in Table 7.1, especially by the comparison of the properties between methacrylate-based polymer monoliths and silica monoliths. 

During the past 10 years, in addition to silica-based monoliths [12], a broad range of organic polymeric monoliths has been studied. Their most advantageous attribute is their chemical stability over a wide pH range. The most common organic monoliths were the results of methacrylate [13] and styrene [14] monomers. Some examples that confirm the utility of monolithic columns in IPC are described below. 

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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