Monolithic rods

FIGURE 13.7 Scanning electron micrograph showing flow-through channels in silica-based monolithic rods. 

Other fields using short monolithic units are solid phase synthesis and combinatorial chemistry. Hird et al. [102] predicted that having a single polymer particulate block of porous polymer or monolith would allow the optimization of automation in the field of solid phase (combinatorial) synthesis. They have developed a method for the preparation of monolithic rods, which were then cut into discs of 1.0 to 2.5 mm thickness and used for solid phase synthesis. They... 

In contrast, monolithic materials are easily amenable to any format. This has been demonstrated by using short monolithic rods prepared by copolymerization of divinylbenzene and 2-hydroxyethyl methacrylate in the presence of specifically selected porogens [93]. Table 2 compares recoveries of substituted phenols from both the copolymer and poly(divinylbenzene) cartridges and clearly confirms the positive effect of the polar comonomer. 

In general the preparation of a polymer monolithic rod is performed as a multi-step procedure (Figure 11). Generally, the stages involved are pre-treatment and preparation of the monolithic matrix by polymerization and derivatization or functionalization. Pre-treatment of the bare capillary is sometimes needed in order to obtain good physical stability. Most columns are therefore polymerized in silanized columns. The capillary column is first washed with a strong alkaline solution such as 1.0 M sodium hydroxide so that the siloxane groups at... 

Because of the fact that organic polymers are known to suffer from swelling or shrinkage on changing the solvent [73,74], the inner wall of the column housings (fused silica capillaries or borosilicate columns) has—prior to polymerization—to be derivatized in order to provide chemical attachment of the monolith rod to the wall. 

FIGURE 1.4 Morphology and porosity of a typical monolithic rod, prepared by copolymerization of silane precursors, (a) SEM micrograph of the fractured surface of a monolithic silica gel rod. (b) Pore size distribution of a representative monolithic silica rod. (Reprinted from Guiochon, G., J. Chromatogr. A, 1168, 101, 2007. Copyright 2007, with permission from Elsevier.)... 

Mesoporous materials were originally synthesized in irregular bulk or powder forms, which could limit their applications in separation, optics, electronics, and so on. Thus, it is highly desirable to produce mesoporous materials with controllable macroscopic forms. So far, mesoporous materials have been synthesized in a variety of forms including thin films, spheres, fibers, monoliths, rods, single crystals, and nanoparticles. The acidic synthetic route (S+X I+) developed by Huo etal. appears to be the most appropriate for the morphological control of mesostmctures. 

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. 

Q, S, and E) Fractoflow, Chromolith Merck (Germany) Hollow fibers, monolithic rods Polyamide, silica lEX, RP... 

CIM disk BIA (Slovenia) Monolithic rods, disks, mbes Polyglycidyl lEX, RP, AF... 

Petro M, Svec F, Gitsov I, and Frechet JMJ. Molded monolithic rod of macroporous poly(styrene-co-divinylbenzene) as a separation medium for HPLC of synthetic polymers. Anal. Chem. 1996 68 315-321. 

Bones, J. et al., Using coupled monolithic rods for ultra-high peak capacity LC and LC-MS under normal LC operating pressures, Analyst, 133(2), 180, 2008. 

A small, 20 X 1 mm ID, monolithic rod, obtained by the polymerization of 80% tec/i-DVB in a mixture of dodecanol and toluene, was employed for the solid-phase extraction of polar organic compounds from aqueous solutions [415]. It was demonstrated again that by maintaining constant dilution of the monomer and changing only the weight percent ratio of toluene to dodecanol from 2 58 to 10 50, it is possible to increase the surface area of the sorbent from 188 to 348m /g and to reduce the mean pore diameter... 

MiHuStUe Structures Contiauous porous structures are the other popular type of alternatives to padced beds. They can be formed in many different forms, such as flat disks or as long rods or as anything in between. Flat disks have occasionally been called membranes and have been compared to stacked membranes (21). Monolithic rods have been compared to chromatographic columns (22). They are typically prepared in situ (although this is not a necessity) in the cavity that will also form the containment for use. 

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]. 

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