Environmental Engineering Reference
In-Depth Information
Condenser
Thimble
Glass wool plug
Sample
Aluminium beaker (cup)
Hot plate
Figure 7.11 An automated Soxhlet extraction apparatus (Soxtec) (U.S. EPA, 1994)
60 min. Extraction is faster because of the rigorous contact between the boiling
solvent and the sample. In the second stage, the sample-loaded thimble is lifted
above the boiling solvent. The condensed solvent drips into the sample, extracts the
organics, and falls back into the solvent reservoir. This takes about 60 min. The third
stage is a concentration step for 10-20 min, the solvent is evaporated to 1-2 mL, as
would occur in a K-D concentrator (Chapter 6). Since the concentration step is
integrated in Soxtec, the extract is ready for clean-up and analysis.
7.3.5 Ultrasonic Extraction
A solid sample of 30-g or 2-g, depending on whether the concentration of an
individual organic component is below or above 20 mg/kg, is mixed with anhydrous
sodium sulfate (Na 2 SO 4 ), then extracted three times with one of the variety of
solvent mixtures (1:1 acetone:CH 2 Cl 2 ; 1:1 aetone:hexane). Anhydrous Na 2 SO 4 is
needed to sorb the water and form the free-flowing powder. The extraction uses an
ultrasonic disruptor horn of at least 300 watts power for agitation of the mixture to
ensure its intimate contact between solvent and matrix. The ultrasonic extraction
needs only a few minutes, but extraction efficiency is usually low. The U.S. EPA
recommends this method (3550B) for extracting nonvolatile and semivolatile
organic compounds from soils, sludges, and wastes. This method is not appropriate
for applications where high extraction efficiencies of analytes at very low
concentration are necessary. In addition, there are also concerns that the ultrasonic
energy may lead to breakdown of some organophosphorous compounds. As a result,
this extraction should not be used for some organophosphorous compounds without
an extensive validation.
 
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