Monolithic stationary pahses consist of a porous polymer block. To create the polymer, monomer and cross linker molecules as well as molecules beraing the interactive groups (e.g., an ionomer in the case of IEX) are polymerized in the presence of a porogen directly inside the column. The porogen is a good solvent for the molecules of te start mixture but a nonsolvent for the polymer. As the polyemr forms it “precipitates” into small coils, which subsequently aggregate into “nodules”. Due to the high cross linking, the nodules can be considered “non porous” from the viewpoing of biochromatography. The channels, which are formed between the aggregates, have average channel diameters between 1-5 um. Such columns are still porous enough to permit injection  and washing/regeneration by pressure. The fissured surface structure of the polymer provides a large surface area per unit volume and the capacity of such columns is comparable to that found for the conventional particle based ones. In monolith chromatography, the mobile phase can be considered to flow through the single “particle”. A monolith has more similarities to a bundle of capillaries than to a packed particle bed, and a recent treamtnet of the theory of monolith disk chromatogrpahy uses this approach to model the separations. Monolithis disks and monolithic columns have many similarities. A major difference is the lenght of the separation distance. For monolithic disks, this distance is only in the millimeter range. (UNO Q and UNO S respectively). (Ruth, “Novel approaches to the chomatography of proteins” Biotechnoly and Bioprocessing/Biotechnol. Bioprocess. 27, 2003 455-502)

A monolith is a continuous bed consisting of a single piece of a highly porous solid material where the void volume is decresased to a minimum. The most important feature of this medium is that all the mobile phase is forced to flow through the large pores of the medium. As a consequence, mass transport is enhanced by convection and has a positive effect on the seapration. Three types of monolithic supports are commercially avialble. (Urthaler (US2004/0002081).

 Specific Types:

Chromatographic monoliths have beomce commercially available in various forms. One example is the convective interaction media (CIM) disks produced by BIS d.o.o., Slowenia. These are flat (diameter in the centimeter range, thickness in the millimeter range) disks on the basis of a poly(glycidyl methacrylate-co-ethylene dimethacrylate) copolymer. Currently, the disks are available as strong and weak cation and anion exchanges. They can also be used directly to immobilize proteins and peptides in a very efficient way, since the base polymer in the underivatized state contains epoxy groups. The seoncd commercially avilalbe monolithic stationary phase is the UNO column by Bio-Rad. These monoliths have a typical column dimensions, with a lenght in the centimeter and diameter in the millimeter range. UNO columns are availabel as strong cation and anion exchangers (UNO Q and UNO S respectively). (Ruth, “Novel approaches to the chomatography of proteins” Biotechnoly and Bioprocessing/Biotechnol. Bioprocess. 27, 2003 455-502)

Silica gel based monolithic beds: are slid robs of slica monolith that have been preapred according to a sol-gel process. This process is based on the hydrolysis and polycondensation of alkoxysilanes in the present of water-soluble polmyers. The method leads to “rods” made of a single pieces of porous silica with a defined bimodal pore structure having macro (about 2 um) and mesopores (about 0.013 um) when smaller ordes intended for analytical purposes are preapred.

Polyacrlamide based monolithigc beds: are mode of swollen polyacrlamide gel compressed in the shape of columns. Their technology relies on the polymerization of advanced monomers and ionomers directly in the chromatographic column. In the presence of salt, the polymer chains form aggregates into large bundles by hydrophobic interaction, creating voids between the bundles large enough to permet a high hydrodynamic flow. (Urthaler (US2004/0002081).

Rigid organic gel based monolithic beds: These supports are preared by free radical polymerization of a mixture of a polymerizable monomer, optionally with functional groups, such as glycidyl methacrylate, ehtylene diemtacrylate, a crosslinking agent, a radical chain initaitor and porogenic solvents in barrels of an appropiate mold. (Urthaler (US2004/0002081).