Extraction of Total Petroleum Hydrocarbon Contaminants (Diesel and Waste Oil) in Soils by Accelerated Solvent Extraction

INTRODUCTION Underground storage tanks containing hydrocarbonbased fuels are found worldwide. Many of these tanks have leaks, allowing gasoline, diesel, oil, or other hydrocarbon materials to contaminate the surrounding soil. In 1992, only 2 million of the 5 million tanks in the U.S. were monitored for leaks. However, underground storage tanks represent only one of many sources of hydrocarbon contamination in soils. Obviously, the ability to determine the level of hydrocarbon contamination in soils is important. In the United States, U.S. EPA Methods 3540 (Soxhlet) and 3550 (ultrasonic) are presently used for the extraction of hydrocarbons from soils prior to the analytical determination. Similar methods are used worldwide. Soxhlet extraction is time-consuming (four or more hours) and requires 250–500 mL of solvent for 10to 30-g samples. Ultrasonic extraction requires 150– 500 mL of solvent and is a labor-intensive method requiring multiple extractions, decanting, and filtering steps for each sample. Accelerated Solvent Extraction (ASE) is an innovative sample preparation technique that combines elevated temperatures and pressures with liquid solvents to achieve fast and efficient removal of analytes of interest from various matrices. With ASE, extractions can be done in very short periods of time and with minimal amounts of solvent compared to conventional sample extraction techniques such as Soxhlet and sonication. For example, 10-g dry samples can be completely extracted in less than 15 min with less than 15 mL of solvent. ASE has been demonstrated to be equivalent to existing extraction methodologies, such as Soxhlet and automated Soxhlet, for most RCRA (Resource Conservation and Recovery Act) analytes from solid and semisolid samples. ASE meets the requirements of U.S. EPA Method 3545, Pressurized Fluid Extraction. The analytes included in Method 3545 are the semivolatiles (BNAs), organochlorine and organophosphorus pesticides (OCPs and OPPs), polychlorinated biphenyls (PCBs), polychlorinated dibenzo-pdioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and chlorinated herbicides. This application note reports on the use of ASE for the extraction of diesel range organics (DRO), waste oil organics (WOO), and total petroleum hydrocarbons (TPH, the sum of DRO and WOO) from soils.