Affinity-based solid phase extraction

Many compounds have now been used as template molecules in molecular imprinting. Basically, imprinted polymers can be used directly as separation media. Since all separation applications cannot be described here, some studies recently reported are bsted in Table 7.1. In this chapter, only selected topics, including sensor applications, signaling polymers, molecularly imprinted sorbent assays, molecularly imprinted membranes, affinity-based solid phase extraction, in situ preparation of imprinted polymers, and molecularly imprinted catalysts are discussed. For the reader requiring information on other applications, there are many review articles dealing with these, Recent review articles and books are summarized in Table 7.1. For further development of molecular imprinting techniques, newly designed functional monomers would be desirable. Various functional monomers have been reported and many applications have been conducted. These are summarized in Table 7.2. 

Fluorous affinity separation was originally used to remove catalysts from complex reaction mixtures [6], A perfluoroalkyl moiety (generally no shorter than -C6F13) is appended to a compound of interest. Tagged molecules are then rapidly separated from other components in the mixture by either liquid-liquid extraction or liquid-solid-phase extraction. Fluorous affinity-based separation has recently been used in biomolecule purification, proteomics, and microarray experiments [15-20],... 

Solid-phase extraction (SPE) is a procedure in which an analyte, contained in a liquid phase, comes in contact with a solid phase (sorbent particles in a column or disk) and is selectively attracted to the surface of that solid phase. All other materials not adsorbed by chemical attraction or affinity remain in the liquid phase and go to waste. A wash solution is then usually passed through the sorbent bed to remove any loosely adsorbed contaminants from the sample matrix, yet retain the analyte of interest on the solid phase. Einally, an eluting solvent (usually an organic solvent such as methanol or acetonitrile that may be modified with acid or base) is added to the sorbent bed. This solvent disrupts the attraction between the analyte and solid phase that cause desorption,... 

To make effective use of fluorous biphasic systems, the fluorous phase may also be a stationary phase. Fluorous compounds or compounds carrying fluorous ponytails have high affinity for fluorous reversed-phase silica gel [Ic, 13] which has been modified by means of a fluorous silane [14]. This effect has been used to achieve convenient isolation and purification of a variety of compounds with high fluorine content, first by simple solid-phase extraction (SPE) [15] and later by chromatography with a mobile phase based on a fluorophilicity gradient [16]. 

Most methods for mycotoxins detection are based on HPLC using reversed phase colnmns followed by flnorescent detection. The methods used for purifying the sample are solid-phase extraction column (SPE) with normal phase or reversed phase absorbents. Recently, immune affinity colnmns have been used more often. 

One application example on the microfluidic LSI platform is the extraction of nucleic acids (NA) from a small amount of cells [126, 127] for cell-based assays. For the extraction of NA from a cell suspension, the cell membrane has to be destroyed first (chemical lysis of the cell). Afterwards, the NA are specifically separated from the residual cell components using a solid phase extraction method based on an NA affinity column (paramagnetic beads). This extraction protocol is completely implemented on the microfiuidic... 

Molecular imprinting for solid phase extraction has attracted increasing interest in the past few years. MIP-based SPE is now considered to be the first commercialization effort to market the imprinting technology. As in other related applications, success in this aspect largely depends on the performance of MIP adsorbents under real conditions. In addition to strive for very high binding affinity and specificity, perhaps more important issues, but not so much foreseen by many of the research... 

High-performance affinity chromatography has recently been reported with trypsin-modified avidin supported on 5 pm silica. While the separations were successful and a wide range of foods were studied, elution times were 80 minutes and ADAM post-column reactions were still required (Hayakawa et al. 2009). However, such affinity columns within a solid-phase extraction (SPE) platform make realistic choices for sample preparation, whereby the biotin can be purified and concentrated prior to reversed-phase HPLC. R-Biopharm has recently developed a commercially available antibody-based immunoaffinity column to bind biotin from aqueous extracts, providing an excellent technique to clean up complex samples. 

A new tag strategy, termed syndiesis based on affinity separation (SAS) , was developed for high throiq)ut synthesis of organic conq)oimds. In this method, the desired tagged conq)ound was separated from the reaction mixture by solid-phase extraction using specific molecular recognition. The interaction between a crown ether (32-crown-lO) and ammonium ion and the interaction between a barbituric acid derivative and its artificial receptor were used for SAS. 

Several methods have been used to separate the lanthanides chemically solvent extraction, ion exchange chromatography, HPLC using Q-hydroxyisobutyric acid and, in limited cases, selective reduction of a particular metal cation.40-43 The use of di(2-ethylhexyl)orthophosphoric acid (HDEHP) for the separation of various rare-earth elements via solvent extraction has also been reported.44 16 This separation method is based on the strong tendency of Ln3+ ions to form complexes with various anions (i.e., Cl- or N03 ) and their wide range of affinities for com-plexation to dialkyl orthophosphoric acid. When the HDEHP is attached to a solid phase resin, the lanthanides can be selected with various concentrations of acid in order of size, with the smallest ion being the most highly retained. 

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