Despite the advances that have been made in the sensitivity and selectivity of analytical instrumentation, for complex samples
encountered in environmental and food matrices, some form of sample pretreatment almost always is required to isolate the
analytes of interest. For liquid samples, the use of liquid–liquid extraction (LLE) and solid-phase extraction (SPE) have
been the most popular approaches to pretreat these samples. Many methods have been published using one or both of these techniques
to simplify complex mixtures before chromatographic or spectroscopic analysis. In some cases, LLE has given way to SPE because
there has been a trend to eliminate or reduce the consumption of organic solvents, especially chlorinated solvents. Even though
there have been many new SPE sorbents introduced that provide more selective interactions, workers still prefer to use nonselective
hydrophobic sorbents for their sample preparation needs (1). Even in sorbents considered to be more selective, such as ion
exchange SPE packings, analyte retention is often highly influenced by hydrophobic interactions with the organic portion of
the sorbent surface. When these interactions occur, coextraction of other analytes and matrix interferences generally occurs,
often a big problem when the analytes of interest are in trace concentrations. Then, additional cleanup procedures are required,
increasing the chance of analyte loss and contamination by the introduction of other chemical species.
Thus, there is a need for cleanup methods that will result in more selective extraction of the analytes of interest, hopefully
in a single step. In the past decade, there has been an increasing level of interest in the development of highly selective
sorbents based upon immunoaffinity interactions. Such sorbents involve antigen–antibody interactions that are based upon molecular
recognition and, thus, are very specific. The antibodies are immobilized onto solid supports such as silica or polymeric adsorbents
that are classified as immunosorbents (ISs). Then, these sorbents are used in a manner similar to SPE cartridges. The analyte
isolation process is termed immunoextraction or immunoaffinity extraction. Sometimes, when the experiment is performed in
a column format, it is referred to as an immunoaffinity chromatography (IAC) but the process involved is not really a chromatographic
mechanism.
There have been many papers published on the subject of ISs and immunoextraction but only recently have commercial products
become available that can be applied conveniently to real world applications. This installment of "Sample Prep Perspectives"
will be devoted to an introduction to ISs and their potential applications for small molecules that might be encountered as
pollutants in environmental and food samples. For those who would like in-depth coverage, there are a number of excellent
review articles (2–4) and most recently a textbook that has chapters devoted to immunoaffinity and other bioanalytical techniques
(5).
In earlier installments, we have covered immunoaffinity products that were designed to remove high-abundance proteins from
biological samples (6). In principle, these products are similar to those discussed here but are optimized for the immunoaffinity
interactions for large molecules. In addition, an earlier article discussed molecular imprinted polymers (MIPS) (7), that,
in principle, mimic antibodies but involve the formation of a specific molecular imprint (cavity) on the surface of the sorbent
formed by a template molecule while ISs are prepared by the immobilization of an antibody onto the surface of a solid support.
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