Selective Sorbents for Solid-Phase Extraction Based on Molecularly Imprinted Polymers

2 Solid-phase extraction (SPE) is a technique for extracting and purifying analytes in solution. When concentrations of the target analytes decrease, the number of matrix components that can potentially interfere with quantification or identification will increase and create higher demands on the selectivity and sensitivity of an applied analytical method. Many analytical methods comprise a sample-pretreatment step followed by either separation and detection steps that can discriminate to a variable degree between the analyte and the matrix components or quantification in a competitive binding assay.1,2 The general idea is that all elements of a method should contribute to its required sensitivity and selectivity. In many instances, however, bioanalytical sample pretreatment is regarded as a step to get rid of water, salts and bulk amounts of proteins present in the samples. In trace analysis, many other compounds, some of which may have very similar structures to the analytes of interest, are also present in addition to these interferences. These compounds can also interfere with analyses. Highly selective phases that can discriminate and isolate the target analyte from the multitude of other compounds remaining in the sample are desirable. So far, the most selective phases used for SPE are based on immunoaffinity. These immunoaffinity columns strongly contribute to the selectivity of trace analytical methods, especially for identifying pollutants and drug residues.3 It is not without reason that immunoaffinity columns are used less widely for many different compounds because a selective antibody must be developed for each analyte. Developing a specific antibody is a long and arduous process that can take as long as 12 months. Furthermore, because of the costs of producing immunoaffinity columns, long-term use of those columns is necessary. Operational conditions that cause denaturation or mobilization of the antibodies bound to the column should not be used.4–6 An alternative technology, using molecularly imprinted polymers, is currently being extensively evaluated by academic and industrial research groups.7 In this “Sample Preparation Perspectives” column, we will provide relevant background information about the basic principles of molecular imprinting, the advantages and drawbacks of molecularly imprinted polymer use in method development and routine applications, and some examples that illustrate the potential of molecularly imprinted polymers for highly selective SPE.