Macroporous monoliths, for chromatographic separations

Almost all stationary phases used in chromatography have a bimodal pore size distribution. The first mode corresponds to the macropores or throughpores that allow the percolation of the column by the stream of mobile phase. The second distribution corresponds to the mesopores that combine to give the conventional internal porosity distribution described in the previous section. The mesopores are responsible for most of the specific surface area necessary to provide the retention and the saturation capacity that are needed to permit the retention of the mixture components in a good solvent, a condition for chromatographic separation. Nonporous particles have been used with only moderate success because very weak solvents must be used to achieve sufficient retention, which often causes solubility problems, and the saturation capacity of these particles is small. The terms of macro- and meso-pores apply as well to columns made of packed particles and to monolithic columns. 

The first monolithic materials initially emerged in the 1960s, but it is during the last 20 years that monoliths have been intensively developed in a variety of fields and particularly in analytical chemistry for separation techniques. Nowadays, these macroporous materials are widely used and have found numerous applications in different chromatographic modes such as liquid chromatography (LC) or CEC, as indicated by several reviews [150, 151]. Less commonly, monolithic materials can also be applied, for example, to solid-phase extraction, combinatorial synthesis and for enzyme immobilisation. 

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