Molecular Imprinted Polymers for Chiral Separations

Molecular imprinted polymers (MIPs) attracted significant attention in the last decade as chiral stationary phases targeted for the separation of selected compounds used as templates during the synthesis of packing material [88]. 

In the previous sections of this chapter we mainly discussed the properties of HPLC packing materials (adsorbents) and the influence of their physical and chemical properties on HPLC retention. In the following sections we will concentrate primarily on the properties of HPLC column itself. 

A modern HPLC column is either stainless steel or plastic tube filled with packing material (adsorbent) and arranged with end-fittings designed to provide sealed connection with the eluent inlet and outlet lines and to retain packing material inside while allowing liquid to pass through. 

A column is essentially a device that holds a stationary phase in place, allowing the mobile phase to carry an injected sample through and allowing analytes to interact with available surface. As we discussed in Section 3.2, the efficiency is mainly dependent on the column type (packed, monolithic, or capillary) and particle size for packed columns, or through-pore diameter for monolithic columns. 

Comparison of the porous structure of different columns was discussed in Section 3.2 here we emphasize that with a packed column the ratio of particle size to the average interparticle pores (space) is on the level of 3-3.5 while with monolithic columns trough-pores are on the level of 6000 A and silica material is only about 1 u thick, which makes this ratio 0.5-0.2 or about 10 times smaller, thus significantly decreasing the time needed for analyte molecules to diffuse into the mesoporous space for the interaction with main surface. This allows for much faster flow rates without the loss of the dynamic equilibrium conditions (otherwise known as the slow mass transfer term (C) in the Van Deemter equation). 

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