The analysis of contaminated soil and sludge samples for semi-volatile organic compounds (SVOC) has traditionally been performed using gas chromatography/mass spectrometry (GC/MS) (EPA SW-846, Method 8270). This method relies on the extraction of contaminants from the samples utilizing a variety of organic and chlorinated solvents. Pressurized fluid extraction (EPA SW-846, Method 3545) has been shown to efficiently extract SVOC contaminants from soil using methylene chloride as the extraction solvent. This technique minimizes the use of organic solvents but still requires a lengthy evaporation step.
The major areas of concern regarding traditional extraction techniques are: 1.) laboratory contamination resulting from the presence of organic solvents; 2.) health and environmental impact from the use of organic solvents; and 3.) extended processing times due to the need to evaporate the solvent to concentrate the extract for analysis.
In response to these concerns and limitations, we report preliminary studies utilizing pressurized fluid extraction on a Dionex Accelerated Solvent Extractor 200 (ASE) with methanol/water as the extraction solvent for recovery of SVOC from soil samples. The soil samples were spiked with the SVOC listed in EPA SW-846, Method 8270 at the 167ppb level. The compounds in the aqueous extracts were then acidified and reconcentrated using Stir Bar Sorptive Extraction with PDMS-coated stir bars prior to analysis by thermal desorption GC/MS. The presence of polar solvents such as methanol, ethanol, or acetonitrile is compatible with partitioning of the SVOC into the stir bar PDMS phase, thus enabling the use of solvent blends with water to optimize extraction efficiency.
Extracting in the ASE with 20% methanol in water under moderate conditions (100C, 1500psi), compounds from phenol to benzo(g,h,I)perylene were recovered from the spiked soil. Generally, the lowest boiling 40 compounds (fluorene and below) showed the best recovery (>90% in the first extraction). The middle 15 compounds (fluorene to chrysene) showed recoveries of >75% in the first extraction. The highest boiling 7 compounds showed approximately equal recovery in two sequential ASE extractions. This suggests the extraction conditions should be optimized further. Detection limits in the mid ppt (pg/g) range appear to be attainable for most compounds.
