Heterogeneous imprinting

These examples demonstrate the versatility of MIP in LC. Although broad peaks caused by the heterogeneity of imprint qualities are often observed for the imprinted species, MIP most certainly present an interesting alternative to traditional stationary phases in LC. 

On the negative side, there is excessive broadening of the elution band caused by a number of features including the heterogeneity of the imprint as noted earlier. 

Figure 15.2 Depiction of the binding site heterogeneity of a molecular imprinted polymer.

Figure 15.3 T3fpical heterogeneous distribution of binding site affinities found in molecular imprinted polymers compared with the homogenous distribution of a typical monoclonal antibody. Reprinted from Umpleby et al. (2001). Copyright 2001 American Chemical Society.

Rampey AM, Umpleby RJ, Rushton GT, Iseman JC, Shah RN, Shimizu KD. Characterization of the imprint effect and the influence of imprinting conditions on affinity, capacity, and heterogeneity in molecularly imprinted polymers using the Freundlich isotherm-affinity distribution analysis. Anal Chem 2004 76 1123-1133. 

Most MIPs show a heterogeneous distribution of binding sites and can be considered as polyclonal in their nature. In non-covalent imprinting, the amorphous material contains binding sites which are not identical because they may have different cross-linking density or accessibility. Moreover, the monomer (M) and the template molecule (A) may form complexes of different stoichiometry (MnA) in the pre-polymerization mixture [5]... 

Most MIP-ILAs are based on a heterogeneous format, as the MIP-bound analyte is separated from the free form before measurement. However, the introduction of soluble imprinted polymers or MIPs that yield stable suspensions has allowed the development of homogeneous ILAs [28, 29]. 

While technically simpler than the covalent approach, the self-assembly approach creates more heterogeneous sites and also requires templates with specific functional groups.8 Since sol-gel chemistry is aqueous based, H-bonding interactions are significantly weaker compared to the conventional organic polymerization methods. Often, hydrophobic effects and ionic interactions are utilized. A number of other examples of the noncovalent approach to imprinting in sol-gel-derived materials are provided in recent reviews.5 17 In the sections below, the focus will be on some of the newer aspects of small molecule imprinting in silica that involve the use of chiral templates... 

The canine community often observes, with disdain, that there is no such thing as waste at an explosive manufacturing plant whatever is left over from one batch almost always ends up in the next. This introduces impurities and heterogeneity into the explosives, something which is welcomed by the trace analyst in the forensic laboratory but despised by experienced trainers wishing to imprint the optimum range of explosive odors on the dogs. 

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