Semivolatile organic compound extraction from liquids

Soil vapor extraction (SVE) (also called vacuum extraction, soil venting, or in situ vaporization) is used to remove volatile organic compounds (VOCs) and some semivolatile organic compounds (SVOCs) from contaminated soil. SVE systems apply a vacuum in an extraction well to remove soil vapors. This creates a negative pressure that causes the volatilization of some chemicals in the vadose zone of the soil. The technology has also been used to extract non-aqueous-phase liquid (NAPE). Contaminant volatilization is often enhanced through the use of air injection wells to supply unsaturated air into the vadose zone of the soil. 

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. ... 

In most environmental laboratories the classical liquid-liquid extraction using the separatory funnel is still the most used technique to extract semivolatile organic compounds, pesticides, and PCBs from aqueous samples. Methylene chloride (MeCl), although a potential health hazard, is one of the most commonly used solvents. Several physical properties make it advantageous to use. These properties are listed in Table 15.5. 

The pressure in PLE is not a significant variable to optimize, because its role is simply to maintain the solvent in its liquid state. The main variables to optimize are extraction time and temperature, which considerably simplifies the experimental design. The main advantages of PLE are fastness (around 15 min), low amounts of toxic organic solvents are required (between 15 and 40 mL), and several samples can be extracted simultaneously (up to 24). However, the instrumentation is much more expensive than Soxhlet or even microwaves. EPA method 3545 uses PLE in the determination of semivolatile organic compounds from solid samples [139], which can be extended to solid devices used to trap PAHs in air monitoring. Furthermore, PLE has proven to be an efficient method to extract analytes from complex samples, with efficiencies comparable to Soxhlet extraction [140],... 

Steam injection and vacuum extraction (SIVE) is a patented, commercially available in situ technology. SIVE has been used to remove non-aqueous-phase liquids (NAPLs), diesel fuel, jet fuel, semivolatile and volatile organic compounds (SVOCs and VOCs), chlorinated solvents, acetone, and benzene, toluene, ethyl benzene, and xylenes (BTEX) from soil and ground-water. 

As discussed in this book, certain sample preparation techniques are clearly more appropriate for volatile compounds than for semivolatile and nonvolatile compounds. In this chapter we concentrate on extraction methods for semivolatile organics from liquids. Techniques for extraction of volatile organics from solids and liquids are discussed in Chapter 4. 

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. 

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