Conventional techniques for environmental organic sample preparation for priority pollutants, such as extractions by shakers, Sohxlet, or sonication, are time-consuming and generate large volumes of solvent waste. In addition, workers are exposed for extended periods to toxic organic solvents. Pressurized solvent extraction uses les solvent, but can only process six samples per hour and is limited in sample size. Microwave-assisted solvent extraction is a time-proven technique that is fast, uses significantly less solvent than traditional techniques, and is cost-effective. It is also an approved procedure for the extraction of semi-volatile organic compounds of interest from soils, sediments, clays, sludges, and solid waste as listed in USEPA Method 3546. ASTM has also approved the microwave method for Total Petroleum Hydrocarbons (TPH) in addition to semi-volatile compounds.

The MARS 6 Microwave Sample Preparation System is ideal for USEPA 3546, as well as other solid-liquid extractions. Up to 40 vessels may be processed simultaneously, providing the highest throughput available for busy labs. Utilizing an industry-leading 1800 watts of microwave energy, the MARS 6 offers unprecedented power and control with CEM’s patented PowerMAX™ Technology. The system also features preprogrammed One Touch™ Methods, including USEPA 3546, which can be accessed via the large, full-color touchscreen interface. Using One Touch Methods, the MARS 6 automatically recognizes the vessel type, counts the number of vessels, and determines the optimum parameters for a fast, efficient extraction.

Utilizing a 40-place MARSXpress turntable, 20 g of EPA Priority Pollutant CLP soil was weighed into each 75-mL vessel and 25-mL of acetone:hexane 1:1 (v/v) was added. The easy-to-use, 3-part vessels were assembled, loaded onto the turntable and placed in the MARS 6. The One Touch Method for USEPA 3546 was selected and the run started.

Following the prescribed method for USEPA 3546 requiring temperature and pressure conditions of 100 – 115 oC and 50 – 175 psi, the power was set to 100% at 1800 watts with a Ramp Time of 15 minutes and a Hold Time of 10 minutes. The MARS 6 is unique in its ability to measure and control the temperature of all 40 vessels. As it regulates the run based on the most reactive vessel and can switch control rapidly from one vessel to another, the system ensures that the proper extraction conditions are met for each sample in the batch. This information can be conveniently printed out in a bar graph for documentation (Figure 1). Due to advanced vessel architecture and the high performance design of the airflow system, vessels cool quickly in the MARS 6 without the need for external blowers or water baths.

As observed in the Chlorinated Pesticide Residue Recovery data in the chart, the MARS 6 offers better results than conventional methods. In addition, 500 extractions may be performed in the MARS 6 with the same amount of solvent needed for 32 Soxhlet extractions. The ability to batch up to 40 samples provides laboratories with the lowest cost per test available.