Environmental analysis of soil samples for Semi-Volatile Organics (SVOCs), Pesticides, Herbicides, and Polychlorinated biphenyls (PCBs) traditionally require solvent intensive methods such as sonication or Soxhlet extraction. Accelerated Solvent Extraction (ASE) is a method recently accepted by the U.S. Environmental Protection Agency (EPA) for the extraction of the test compounds from solid matrices. ASE is a fully automated system, requiring far smaller quantities of solvent than traditional methods. ASE also allows for the use of less hazardous solvents such as acetone and hexane in the place of methylene chloride.
Applicable Regulations
US-EPA SW-846 Third Edition Method 3545.

Overview of Procedure
ASE is an automated system for the extraction of environmental analytes from soils and other solid matrices. A 10 - 30 gram sample is mixed with a drying agent (sodium sulfate), placed in the extraction tube, heated, and the solvent extracted. The resulting extract is transferred to a 60 ml vial for further concentration and analysis.

Waste Minimization Procedure
The volume of waste generated is minimized by performing the extraction procedure at elevated temperature and pressure. A sonication extraction is performed by sonicating 30 grams of sample in 100 ml of methylene chloride. In order to get a thorough extraction of the target compounds, the procedure must be performed three times. This procedure results in 300 ml of total solvent for each sample. Soxhlet extraction is performed by a distillation process where 300 ml of solvent are distilled in a 500 ml boiling flask. Solvent vapors are condensed, and the condensate passes through the sample as it is returned to the boiling flask. As the condensate passes through the sample, target compounds are extracted and deposited in the boiling flask. After a 12 - 24 hour extraction, analytes of interest have been removed from the sample and are now present in the 300 ml of solvent. In order to achieve required sensitivity, the extract is concentrated to a final volume of 2 - 10 ml. Some samples are also solvent exchanged from methylene chloride to hexane.

equip.gif (22284 bytes)Because ASE extractions are performed at pres- sures greater than 1000 psi, solvents can be heated to temperatures in excess of their normal boiling point. This results in a much more efficient extraction process. The ASE200 (below) is able to completely extract samples in less than 20 minutes, and final solvent volumes are less than 50 ml.

Also, because of increased extraction efficiency, hexane can often be used for the extraction, and thus no solvent exchange is required.

Additional waste minimization occurs because the ASE200 requires less glassware and sample extract drying. Traditional sonication and Soxhlet extractions require solvent rinsing of all glassware and drying agents. Rinsing requirements result in the use, and subsequent disposal, of approximately 100 ml of methylene chloride, 50 ml of acetone, and 100 ml of hexane per sample. ASE extraction procedures require only 20 ml of solvent (hexane or methylene chloride depending on analysis) per sample for rinsing.

In summary, use of the ASE200 will result in the use of far less solvent than traditional methods. Approximately 500 ml less solvent per sample will be used, and subsequently collected for disposal.

Known Limitations
ASE200 technology is currently approved for all soil/sludge waste. Michigan Department of Environmental Quality/EPA approval is not yet available for the extraction of pesticides/PCBs from polyurethane foam (PUF) filters used in air monitoring.

Safety & Health Precautions/Personal Protective Equipment Follow all applicable safety and health protocols and regulations as established by your institution.

Benefits Benefits derived from the implementation of ASE technology should be recognized immediately. Waste solvent reduction of approximately 500 ml per sample can be expected. A reduction in the amounts of solvents that the U-M Environmental Laboratory will also be required to have stored on site will be realized.

Cost savings will be achieved in a number of ways. Less solvent will be required to be purchased. Less glassware will be required, limiting replacement costs of broken glassware. The system's automation will also reduce analyst cost. Currently, sonication or Soxhlet extractions require 30 to 40 minutes of analyst time per sample. ASE200 will only require 5 to 10 minutes per sample, resulting in increased analyst productivity. Furthermore, extraction time will be shortened, resulting in quicker sample turn around time and greater customer satisfaction.

ASE technology is a recent development in the environmental field. Its ability to perform as a laboratory workhorse and comparisons to traditional methods have not yet been determined. It appears though, with proper analyst experience and method development, ASE technology should perform as well, if not better, than the traditional extraction methods.

There are two apparent reasons why the ASE200 has not yet become commonplace in environmental laboratories. First is EPA approval. SW-846 was updated in summer 1997; this newly promulgated version is the first to include accelerated solvent extraction as an approved method. Second is setup cost. Traditionally, new technology is expensive. As systems become accepted and more laboratories purchase the ASE200, its cost should decrease. Until then, the initial price of the instrument will require a significant investment.

Project Related Costs
Initial setup costs for the ASE200: Approx. $50,000

Traditional methodology price per sample*: $16/sample

ASE200 methodology price per sample*: $5/sample

Net savings per sample*: $11/sample

*All costs are based on laboratory estimates.

Based upon the estimated net savings, a simple payback calculation may be performed. If the equipment were being used to full capacity, laboratory personnel could load 24 samples at the beginning of the shift, which would be automatically processed over the next 8 hours. At the end of the shift before leaving for the evening, laboratory personnel could load another 24 samples to be processed overnight. Given that 12 of the samples would be required for quality control purposes, the maximum sample output would be 36 samples in any given 24 hour period.

Using the calculated net savings of $11.43 per sample given above, the cost savings per day amount to $411.48. If the initial setup costs are $50,000, the simple payback period then amounts to 122 days ($50,000 $411.48/day), or approximately six months based upon a five day workweek.