Simple troubleshooting tips for dealing with common issues that can delay your Soxhlet extractions.
Soxhlet extraction: a simple, user-friendly way to get the components you’re interested in out of your sample. Its clever solvent-recycling mechanism provides a cost-efficient way to get maximum extraction.
However, as with many experimental procedures, minor hiccups are common when setting up a new extraction. Rest assured that many of these are easily resolved with small changes to your setup or protocol.
In this blog, we have listed a few common issues—together with simple things you can do to keep your extractions running smoothly.
1. No solvent evaporates (or not enough)
If there is little or no evaporation from the solvent reservoir, the problem usually lies in the solvent or the heating element. Check whether the heating element is working correctly and whether it reaches the temperature you need for your extraction.
If you require faster evaporation without altering the temperature, then a change of solvent might be an option. There are several commonly used solvents for Soxhlet extraction, all with different properties and boiling points. If a solvent with a lower boiling point is suitable for your application, it might improve evaporation speed.
2. I’m not extracting the right compounds
The compounds you extract from your sample depend almost entirely on the solvent, and each commonly used solvent comes with its own benefits and drawbacks. Hexane, for example, is a popular choice, because it readily dissolves polar compounds. It is also easy to retrieve after the extraction is complete.
Ethanol, on the other hand, has the ability to dissolve both polar and nonpolar molecules due to the combination of a polar hydroxyl group and a nonpolar ‘tail’. Ethanol can also break the tough cell walls of plant samples, which helps in the extraction of intracellular compounds.
3. The solvent is not syphoning back
If after passing through the sample the solvent does not syphon back into the reservoir, a simple trick is to try heating up the syphoning tube slightly, for example by using a hairdryer. If this has no effect the most likely cause is a blockage.
To prevent sample-material blockages, make sure to use a thimble that precisely fits inside your Soxhlet extraction apparatus. Soxhlet extraction thimbles are available in a range of sizes to fit different extractors and prevent blockages.
4. I’m not sure which thimble to use
Soxhlet extraction thimbles can be made from different materials, but most scientists use high-purity cellulose or glass fiber thimbles. Both materials have broad solvent compatibility and suit many common applications of Soxhlet extraction.
To confirm solvent compatibility when using a new protocol or a new type of thimble, you can carry out a blank run with an empty thimble. Blank runs also help to check for ‘extractables,’ which are compounds released from the thimble itself that might interfere with analysis.
If extractables are a concern—even with good solvent compatibility—then prewashing the thimble is an option. Prewashing with a small amount of pure solvent is a fast way of removing potential contaminants from the thimble before starting the extraction.
At Cytiva, we provide high-quality thimbles made from pure alpha cellulose or borosilicate glass for reliable Soxhlet extractions. All our thimbles have broad solvent compatibility and very low levels of extractables—minimizing the need for prewashing.
Our team of experts is trained in troubleshooting filtration and can advise on which thimble is most suitable for your Soxhlet extraction. Contact your local Cytiva representative to discuss your needs.