Polyacrylamide monoliths, preparation

Preparation of Polyacrylamide Monoliths Hjerten et al. [149] introduced the monolithic stationary phases based on acrylamides in the late 1980s. The cross-linked polyacrylamide can be directly synthesized within the mold by a one-step free-radical chain polymerization. Acrylamide, methacrylamide, or piperazine diacrylamide are often employed as monomers, while V,V -methylene-fcM-acrylamide is used as a cross-linker. 2-Acrylamido-2-methylpropane sulfonic acid, vinylsulfonic acid, butyl methacrylate, or stearoyl methacrylate are usually added to the polymerization mixture to provide charge and functional groups [140]. 

Three main types of polymer-based monoliths are polymethacrylate-based monoliths where methacrylate forms the major component of the monomers for polymerization, polyacrylamide-based monoliths where cross-linked polyacrylamide is synthesized directly within the capillary, and polystyrene-based monoliths that are usually prepared from styrene and 4-(chloromethyl) styrene as monomers and divinylbenzene (DVB) as the cross-linker. 

Another successful example is the separation of a series of steroids listed in Fig. 6.11 using a monolithic capillary column prepared by redox initiated polymerization of a solution of acrylamide 4, methylene bisacrylamide 5, vinylsulfonic acid 12, and dodecyl acrylate 18 in N-methylformamide/TRIS-boric acid buffer (pH 8.2) to which polyethylene glycol) (MW 10,000) was added (overall composition 5% T, 60% C, 10% vinylsulfonic acid, 15% lauryl acrylate, 3% polyethylene glycol)). The capillary tube was first vinylized and its part beyond the detection window was coated with linear polyacrylamide to avoid band broadening. Since laser induced fluorescence was used to decrease the detection limit of the method to about 100 attomoles for neutral steroids, all of the analytes were first tagged with dansylhydrazine. Fig. 6.12 shows an... 

Hjerten and his research group [41] introduced monolithic columns based on acrylamides as chromatographic separation media in the late 1980s. Xie et al. [42] prepared rigid porous polyacrylamide-co-butylmethacrylate-co-A,A -methylene-bis-acrylamide monolithic column for hydrophobic interaction chromatography. They also prepared polyacrylamide-co-At, M-methylene-bis-acrylamide monolithic rods and smdied the effect of polymerization conditions on rods morphology. 

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. 

Xie et al. [47] prepared rigid porous polyacrylamide-co-butylmethacrylate-co-V,V -methylene-fcii-acrylamide monolithic columns with controlled hydrophobicity for chromatographic separation of proteins. They also prepared porous hydrophilic polyacrylamide-co-V,V -methylene-(>w-acrylamide monolithic rods using alcohols with different carbon chain lengths (from methanol to decanol) as poreforming agents [150]. 

Monohthic CEC columns are formed from both organic polymers and silica and the first appUcation involved a swollen hydrophilic polyacrylamide gel, similar to that used in capillary gd dectrophoresis [71]. Polymeric monoliths based on acrylamide, methacrylate and styrene, etc., are prepared in a mold by thermally or UV-initiated polymerization of the monomers, and new developments regarding their preparation have been reported in recent years [25]. 

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