Ever wonder whether the automated Soxhlet extraction would work for your projects?

There are several EPA methods for extracting soil or solid samples for semivolatile analysis.  These include Soxhlet, Microwave, Sonication and others.

The Soxhlet extractor was invented by the German agricultural chemist Prof. Dr. Franz von Soxhlet in 1879 for the extraction of lipids from solid samples.

EPA Method 3540C involves placing the sample in an extractor and refluxing solvent through it drip-wise for 18 hrs.  The extractor collects solvent until it covers the sample and then is syphoned into the round bottom flask to continue the refluxing.  It requires a large amount of solvent for refluxing, typically 300 ml.  It also requires very large and fragile glassware that must be disassembled and cleaned between extractions.

EPA Method 3541 involves placing the sample in a small extraction beaker, covering it in solvent (about 135 ml), boiling for one hour, and evaporating down the solvent.  The entire process takes less than three hours.  The extraction beaker is cleaned between each extraction.

Both methods have been shown to acceptably recover a wide range of semivolatile compounds including PAHs and PCBs.   Neither method has an advantage based on analyte recovery.  However, method 3541 achieves a faster extraction due to the heated extraction for one hour.

The main differences lay in the amount of solvent used and the time it takes to perform the extraction (not including extract concentration).  Method 3541 is superior to 3540 in both respects.    Sonication and Microwave are even better.  Comparison between the methods is illustrated below.