## 3 MIPs' Applications
### MIPs in Separation Techniques  
Molecularly Imprinted Chromatography is one of the most traditional applications of molecularly imprinted polymers [20, 33, 73] especially for Liquid Chromatography (LC) [74, 75] with MIPs usually synthesized by bulk polymerization, ground and sieved mechanically and subsequently packed in a chromatographic column [22]. However, the mechanical processing leads to irregular particles with relatively broad size distribution, resulting in packing of irreproducible quality. For this reason monolithic molecular imprinting columns have been recently prepared directly inside stainless steel columns or capillary columns [76, 77]. The monolithic MIPs have fewer nonselective sites than the conventional bulk MIPs particles, even if the polar porogen used for MIPs synthesis can give poorer enantiomeric separation. Many efforts to decrease heterogeneous size distribution have been made also by preparing spherical and monodispersed beads as HPLC stationary phases. Experimental data suggest that not always uniform MIPs particle sizes allow better chromatographic performances. For instance, precipitation polymerization was used to prepare spherical beads but with a total pore volume still lower compared to irregular particles obtained by bulk polymerization and it has been seen that the particles porosity of the beads strongly influences the chromatographic performance of these systems [78]. In fact the calculated pores volume of 0.38 mL/g obtained for beads was lower in comparison to 0.64 mL/g observed for irregular shaped MIPs prepared with similar reagents. LC has been extensively used to evaluate the recognition properties of MIPs since generally it provides a quicker and easier method for analyzing binding polymer performances. Commonly, the retention behavior (k) of the MIP column, is compared with a reference column packed with the Non-Imprinted Polymer (NIP), to evaluate the imprinting effect which is often expressed by the Imprinting Factor (I\({}_{0}\)) calculated as the ratio between the MIP column and the NIP column (k\({}_{\text{MIP}}\)/k\({}_{\text{NIP}}\)). The MIP sorbents, due to selective interactions exhibited, retain the analyte more strongly than the NIP materials [23]. MIPs were frequently used as Chiral Stationary Phases (MIP-CSPs) in High Performance Liquid Chromatography (HPLC) to obtain enantiomeric resolutions of racemic solutions of different compounds [19], such as amino acid derivatives [74, 79, 80, 81, 82, 83] and drugs [71, 84, 85]. The first studies were made by [PERSON] group that realized an MIP sorbent used as stationary phase in LC, to separate amino acid derivatives [79]. Recently, [PERSON] and co-workers prepared an acrylic polymer by non-covalent imprinting procedure for selective enantioseparation of d or l-Phenylalanine ethyl esters to evaluate the enantio and substrate-selectivity for some amino acid derivates [86]. [PERSON] and co-workers [77] reported studies on the enantioseparation of l-nateglinide by using MIP-CSPs prepared with both bulk and monolithic polymerization process in the same chromatographic conditions. The recognition performances of the monolithic molecular imprinting column showed better performance than the column packed with the polymer obtained by bulk polymerization and this is probably due to the reduction of the number of aspecific binding sites in the monolithic column [87]. However, a limiting factor of monolithic MIP formats is due to the use of porogenic polar solvents required to achieve pore structures of sufficient permeability. The solvent polarity can compete with the template-monomer interactions reducing the affinity of the polymer for the template. It is worth noting that one of the main drawbacks observed in MIPs for HPLC columns, that limit its commercial application, is the excessive peak broadening and tailing. In fact, they are often found in chromatograms for templates when MIP is used as sorbent and they are attributed to the heterogeneity of the binding sites in the MIPs [33].