Solid-phase extraction semivolatile organics from liquids

Sorption tendency is dependent on the characters of the sorbent, the liquid sample (i.e., solvent) matrix, and the analyte. Much of the driving force for extracting semivolatile organics from liquids onto a solid sorbent results from the favorable energy gains achieved when transferring between phases. 

This chapter focuses on three widely used techniques for extraction of semivolatile organics from liquids liquid-liquid extraction (LLE), solid-phase extraction (SPE), and solid-phase microextraction (SPME). Other techniques may be useful in selected circumstances, but these three techniques have become the extraction methods of choice for research and commercial analytical laboratories. A fourth, recently introduced technique, stir bar sorptive extraction (SBSE), is also discussed. 

Figure 1.2 Overview of the EPA s organics protocol. VOCs, volatile organics SVOCs, semivolatile organics OCs/PCBs, organochlorine pesticides/poly-chlorinated biphenyls HS-GC-FID, static headspace coupled to gas chromatography and flame ionization detection LLE, liquid-liquid extraction LSE, liquid-solvent extraction or solvent leaching from solid matrices GC-ECD, gas chromatography and electron-capture detection GC-MS, gas chromatography and mass spectrometry RP-SPE, reversed-phase solid-phase extraction.

Ultrasonic LSE is most applicable to the isolation of semivolatile and nonvolatile organic compounds from solid matrices such as soil, sediment, clays, sand, coal tar, and other related solid wastes. U-LSE is also very useful for the disruption of biological material such as serum or tissue. U-LSE can be coupled with solid-phase extraction (SPE) to give a very robust sample preparation method at relatively low cost in comparison to MAE and ASE approaches. The author has utilized U-LSE/SPE to isolate and recover 9,10-dimethyl-l,2-benzanthracene from animal bedding. A 89% recovery was obtained for bedding that was spiked with this polycyclic aromatic hydrocarbon (PAH) of interest to toxicologists (20). An ultrasonic horn and tip are immersed into a mixture of liquid extractant and solid sample and sonicated at some percent of full power for a finite length of time, either continuously or pulsed. 

The newly developed solid-phase microextraction (SPME) technique, first reported by Pawliszyn in 1989, is increasingly used for the gas chromatographic determination of a wide variety of volatile and semivolatile organic compounds in water or aqueous extracts of different substrates. Basically, it involves the extraction of specific organic analytes directly from aqueous samples or from the headspace of these samples in closed vials. The extraction is achieved onto a fused-silica fiber coated with a polymeric liquid phase. After equilibration, the fiber containing the absorbed or adsorbed analyte is removed and thermally desorbed in the hot injector port of a gas chromatograph or in an appropriate interface of a liquid chromatograph. ... 

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