Development of an Off-Line SFE-IR Method for Petroleum Hydrocarbons in Soils

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Abstract
This paper describes a procedure for the supercritical fluid extraction (SFE) of petroleum hydrocarbons from various soil samples; the extraction is performed at 340 atm and 80°C using supercritical carbon dioxide (at flow rates of 1 to 2 mL/min as liquid) as the extractant. The extracted material is collected in 3 mL of tetrachloroethene. The tetrachloroethene extracts are then cleaned with silica gel (to remove polar organic compounds) and are analyzed by infrared spectrometry. The technique is fairly simple, requiring approximately 30 min for the extraction of a 3-g soil sample and 10 min for extract cleanup and analysis by infrared spectrometry. To develop this procedure, we perform experiments to establish SFE parameters (pressure, temperature, extraction time, and collection solvent) and conditions for the infrared determination. In addition, we perform a side-by-side comparison of SFE (with carbon dioxide) and Soxhlet extraction (with Freon-113), and we evaluate, to a limited extent, the use of carbon dioxide modified with tetrachloroethene as extractant. Single laboratory evaluation of this method indicates that its performance is equivalent to the Soxhlet extraction method with Freon-113. Method accuracy is 80% or better, and method precision is ±20%. The method detection limit is 10 μg/g of sample.

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