To overcome this lack of selectivity highly selective sorbents such as immunosorbents (ISs) (1,2) and molecularly imprinted polymers (MIPs) (3) were developed. They allow extraction, concentration and clean-up in a single step. ISs provide a high degree of molecular recognition because of the high affinity and the high selectivity of the antigen–antibody interactions. Nevertheless, their synthesis involves the production of antibodies which is a time-consuming, tedious and expensive process. An alternative technology that uses MIPs was proposed by chemists; it represents an attractive approach to mimic highly specific antibody binding-sites (4). It involves the copolymerization of functional monomers and cross-linking agents in the presence of an imprint molecule (template), which leads to the formation of a rigid polymer.

The removal of the template results in well-defined cavities within the polymer whose structure and arrangement of functional groups are complementary to the template. However, the template removal is usually uncompleted. This problem is common to all MIP formats; its consequences depend on the final use of the sorbent. In the situation of trace analysis, the template molecules' bleeding gives rise to erroneous results, thus an exhaustive washing of the polymer with a range of solvents should be performed before use to extract the entire amount of the template molecules

Table I: Comparison of the different polymerization methods. Adapted from reference 48 and reprinted with permission

Principle of MIP–SPE

Figure 1