Soxhlet extractor - Definition and Overview

A Soxhlet extractor is a type of laboratory glassware. It was originally designed for the extraction of lipid from a solid test material, but can be used whenever it is difficult to extract any compound from a solid.

Typically, dry test material is placed inside a "thimble" made from filter paper, which is loaded into the Soxhlet extractor. The extractor is attached to a flask containing a solvent (commonly ether or petroleum ether) and a condenser. The solvent is heated, causing it to evaporate. The hot solvent vapor travels up to the condenser, where it cools and drips down onto the test material. The chamber containing the test material slowly fills with warm solvent until, when it is almost full, it is emptied by siphon action, back down to the flask. This cycle may be allowed to repeat many times. During each cycle, a portion of the lipid dissolves in the solvent. However, once the lipid reaches the solvent heating flask, it stays there. It does not participate in the extraction cycle any further. This is the key advantage of this type of extraction; only clean warm solvent is used to extract the solid in the thimble. This increases the efficiency of the extraction when compared with simply heating up the solid in a flask with the solvent.

At the end of an extraction, the excess solvent may be removed using a rotary evaporator, leaving behind only the extracted lipid.