Sorbents in SPE

Appropriate SPE sorbent selection is critical to obtaining efficient SPE recovery of semivolatile organics from liquids. Henry notes that an SPE sorbent ‘‘must be able to sorb rapidly and reproducibly, defined quantities of sample components of interest.’’ Fritz states that ‘‘successful SPE has two major requirements: (1) a high, reproducible percentage of the analytical solutes must be taken up by the solid extractant; and (2) the solutes must then be easily and completely eluted from the solid particles.’’ The sorption process must be reversible. In addition to reversible sorption, SPE sorbents should be porous with large surface areas, be free of leachable impurities, exhibit stability toward the sample matrix and the elution solvents, and have good surface contact with the sample solution.

Obviously, knowledge of the chemistry and character of commonly used SPE sorbents is important to achieving successful extractions. Liska describes developments from the late 1960s until the early 1980s as the ‘‘age of searching’’ for a universal SPE sorbent that culminated in the introduction of polymeric materials and bonded silicas. These sorbents have proven useful for a wide variety of applications. However, the realization that no single optimal sorbent for all purposes exists prompts current efforts to

optimize a sorbent for a particular application, that is, for a specific analyte in a specific matrix. Poole et al. categorize the SPE sorbents available today as either general purpose, class specific, or compound specific. This discussion covers polar, polymeric, bonded silica, and graphitized carbon sorbents of general applicability as well as functionalized polymeric resins, ion-exchange sorbents, controlled-access sorbents, immunoaffinity sorbents, and molecularly imprinted polymers designed for more specific purposes.