Selective Extractions by Molecularly Imprinted Polymers (MIPs)

Sample preparation is often the rate-limiting step in analytical methods and its effectiveness has a critical impact on accuracy, quantification and, ultimately, the precision of any measurement. Traditionally, liquid–liquid extraction methods are frequently used for the extraction of organic analytes from aqueous samples. To overcome some of the disadvantages of liquid–liquid extraction (e.g., its tediousness) solid-phase extraction (SPE) was developed. SPE techniques consume much less solvent, are less labour intensive, reduce exposure to organic solvents and can provide more reproducible results. Traditionally, SPE materials are inorganic (e.g., silica) or organic resin (e.g., styrene-divinylbenzene) based solid sorbents. Silica sorbents can be varied in adsorption character by bonding a wide variety of functional groups to the silica surface. The functionalities can be non-polar, polar, ionic or mixed-mode (e.g., non-polar and ion exchange groups). The surfaces of polymeric resins can also be modified, most commonly by introducing hydrophobic, polar, acidic or basic functional groups. The resulting phases can then operate via both hydrophobic and ion exchange retention mechanisms, as mixed-mode sorbents. Even though hydrophobic, ionic and polar sorbents are widely used for the extraction of trace levels of analytes from complex matrices, the selectivity of such traditional SPE sorbents is often not high, requiring extensive and timeconsuming sample preparation procedures with limited throughput. One solution to the selectivity problem is provided by “immunosorbents” (antibodies or other binding proteins such as “affibodies” immobilized onto a support material), which are widely used in many laboratories for chromatographic separations and analysis of trace compounds in food or biological samples. The limitation in the use of protein-based adsorbents for many small molecule extraction or separation problems is their limited stability in different solvent (e.g., organic) systems and their (often) high cost. The transition to stable, low-cost “selective phases” will be, we believe, the choice of the future for demanding separations. One such group of selective phases is based on the principle of molecular imprinting.