Immunoaffinity sorbents

Immunosorbents The lack of selective sorbents to trap organic analytes in water is certainly the most important weakness of the SPE technique. Selective interactions are involved with immunoaffinity sorbents. 

A recent approach to producing highly selective sorbents for SPE is based on molecular recognition technology and utilizes antibodies immobilized by covalent reaction onto solid supports such as silica (Figure 2.30). Preparation of immunoaffinity sorbents for SPE was reviewed by Stevenson [101] and Stevenson et al. [102], Using immunosorbents, efficient cleanup is achieved from complex biological and environmental samples. 

In a particular case, fluorescein-labelled biotin was used as the solute to be accumulated and anti-biotin -IgG support was the immunoaffinity sorbent the running buffer used was 5 mA/Tris pH 8 at 10 kV (the currents resulting from this arrange-... 

Immunoaffinity sorbents (ISs) are more selective compared to ODS sorbents. The first commercial ISs were introduced for the cleanup of samples for the determination of aflatox-ins (Groopman and Donahue, 1988). ISs have been synthesized for a limited number of pesticides and pesticide classes. Immunosorbents arc formed by covalently bonding antibodies to an appropriate sorbent. Immunosorbent is packed into a solid phase extraction cartridge or precolumn as a classical extraction sorbent (Bouzige and Pichon, 1998). There is much interest in developing ISs for single analytes, which are particularly difficult to analyze at the trace level because of a lack of available extraction methods,. such as acephate and methamidophs. 

In the present context, immunoaffinity chromatography and application of the principle to SPE are more important than IMAC. A comprehensive review (Delaunay-Bertoncini 2004) describes the principles of the immunoaffinity SPE approach for pharmaceutical and biomedical analysis, including its coupling with HPLC and LC/MS as well as examples of other apphcations, e.g., to environmental analysis. An immunoaffinity sorbent contains antibodies that are specific to the target analytes and are immobihzed on a sohd support. An excellent free-access source for detailed information on ah aspects of modern biology (Kimball 2006) includes informative descriptions of antibodies, particularly monoclonal antibodies (see below). 

Prisyazhnoy, V.S.,M. Fusek, andY.B. Alakhov (1988). Synthesis of high-capacity immunoaffinity sorbents with oriented immobilized immunoglobulins or their Fab fragments for isolation of proteins. /. Chromatogr. 424 243-253. 

The low selectivity of the SPE columns currently in use can be increased with more selective sorbents such as the immunosorbents, which have been quite extensively used in SPE-LC (72). Immunoaffinity-based solid-phase extraction (lASPE) sorbents have also been used in coupled gas chromatography for determining... 

Another subset of SPE is immunoaffinity extraction, in which an antibody specific to the analyte is incorporated into the SPE sorbent. This technique is very selective to the analyte and would be very effective in separating the marker residue from tissue-related matrix components. Disadvantages of immunoaffinity extraction are the need to develop a specific antibody-based SPE for each analyte. This approach holds promise for the future as the development of antibody-based methods becomes more commonplace. 

While the above-described sorbents are essentially nonspecific and designed to allow extraction of a wide range of analytes, there are also sorbent phases that are selective toward individual analytes, or at least classes of analytes. These are immunoaffinity (IA) sorbents and molecularly imprinted polymers (MIPs). In the first case, antibodies are immobilized on the solid support used for extraction, and the selective (in the ideal case specific) biochemical interactions allow an antigen to bind selectively to the antibody, whereas the other sample constituents are not retained and... 

New phases will continue to be introduced to take full advantage of specific interactions. The commercialization of immunoaffinity SPE will no doubt occur, especially for compounds that are polar and difficult to recover by the available sorbents of today. Polymers will be refined to enhance the recovery of polar compounds and more new phases will be introduced. Finally, other uses of SPE will be developed and optimized, such as derivatization on disks, and products will no doubt be introduced that make this process routine. At last sampling handling and solid-phase extraction will reach the level of sophistication that its relatives in liquid chromatography have reached, and perhaps go beyond. 

Fig. 7 Chromatograms obtained for water sample a-c) and standard mixture of MC d) in HPLC system with UV detection at 238 mm. Chromatograms for water obtained using extraction with different sorbents a) SPE with Waters Oasis HLB (50 x concentrated), b) with Sepharose-based immunoaffinity column (10 X concentrated), and c) with silica-based immunoaffinity column (10 x concentrated).

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