Soxhlet

Soxhlet is a laboratory extraction apparatus designed for the continuous extraction of lipophilic compounds from solid material. It uses a refluxing solvent that repeatedly passes through the sample, enabling efficient extraction with relatively little solvent.

The device was invented by Franz von Soxhlet in 1879 for fat determination in solids. A Soxhlet extractor typically comprises a boiling flask containing solvent, a thimble housing for the solid sample, a condenser at the top, and a siphon tube that returns the dissolved extract to the boiling flask after each cycle. The solvent vaporizes, condenses in the condenser, drips into the sample chamber, dissolves target compounds, and is siphoned back to the reservoir, where the cycle repeats.

In operation, solvent is heated to reflux in the boiling flask. Vapors condense in the condenser and drip into the thimble containing the sample; the soluble constituents dissolve in the solvent. When the liquid in the thimble reaches the level of the siphon, it is drawn back into the boiling flask, and the cycle continues. This arrangement allows continuous extraction with a fixed amount of solvent over extended periods, typically several hours.

Soxhlet extraction is widely used to recover lipids, essential oils, dyes, and other natural products from plant materials, soils, foods, and environmental samples. Common solvents include nonpolar options such as hexane or petroleum ether, though other solvents may be used depending on the target compounds. Modern variants include accelerated solvent extraction and automated Soxhlet systems, which shorten extraction times while preserving the basic principle. Limitations include long extraction times, solvent consumption, and potential thermal degradation of heat-sensitive compounds.