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What Is a Soxhlet Extractor?

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  • Written By: Mary McMahon
  • Edited By: Shereen Skola
  • Last Modified Date: 17 September 2014
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A Soxhlet extractor is lab equipment designed for processing certain kinds of solids. These devices allow for continuous treatment of a sample with a solvent over a period of hours or days to extract compounds of interest. They are used by chemists in a variety of fields in sample testing, analysis, quality control, and related applications. Suppliers of lab equipment may carry them in a range of sizes, along with accessories.

Early versions of a similar device were in use for thousands of years before a German chemist in the late 1800s lent his name to the invention. The Soxhlet extractor includes a sample suspended inside a larger flask, with a condenser above. To use it, a chemist heats the solvent, which evaporates and travels up into the condenser. Drops of the solvent drip down and into the sample, dissolving the compound.

Once the level inside the sample chamber rises enough, a small tube routes the solvent back to the bottom of the flask, where it can evaporate again and repeat the process. Multiple washings can flush the chemicals of interest from the solid sample into the solvent, where they can be collected for study. The leftover solid is typically discarded, unless a chemist has a specific use for it. Using a Soxhlet extractor can increase the efficiency of the extraction process and allows for a high level of control over the sample being studied.

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Like other laboratory glassware, the Soxhlet extractor has some special features. Manufacturers of scientific equipment use glass specifically designed for this purpose so it will resist cracking and shattering, even in high heat and when exposed to corrosives. Very narrow manufacturing tolerances ensure consistency in lab equipment, right down to the slope of the glass and the bends in the tubing. These are critical to make sure equipment performs reliably, which allows experiments to be tested and repeated.

Between uses, a Soxhlet extractor can be carefully washed and allowed to dry completely, removing all traces of the materials it contained so they don’t interfere with the next experiment. The lab may have a standard protocol for cleaning and drying, also used for consistency reasons. No matter who cleans glassware, the same steps will be followed. In peer reviews of scientific studies, researchers look to determine if every possible variable was controlled, and want to see evidence of protocols for keeping the environment clean to ensure pure results.

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