When a compound of low solubility such as lipid is need to be extracted from a solid mixture a Soxhlet extraction can be carried out. The technique places a specialized piece of glassware in between a flask and a condenser. The refluxing solvent repeatedly washes the solid extracting the desired compound into the flask. The Soxhlet extraction method was described by Soxhlet in 1879, in this procedure; oil and fat from solid material are extracted by repeated washing/percolation with an organic solvent usually hexane or petroleum ether, under reflux in a special glassware. Soxhlet extraction is only required where the desired compound has a limited solubility in a solvent and the impurity is insoluble in that solvent.

Lipids are a group of substances that, in general, are soluble in ether, chloroform, and other organic solvents but are relatively insoluble in water. An accurate and precise quantitative analysis of lipids in foods is important not only for nutritional labeling, but also for determining whether the food meets the standards for identity and uniformity, and for understanding the effects of fats and oils on the functional and nutritional properties of foods. The validity of the fat analysis of a food depends on many factors, including proper sampling and preservation of the sample before the analysis. Because of commercial regulations, it is important for food producers to be able to report fat content in a serving size of a food item.

Figure of Soxhlet extractor

In this method the sample is dried, ground into small particles and placed in a porous cellulose thimble. The thimble is placed in an extraction chamber, which is suspended above a flask containing the solvent and below a condenser. The whole unit is supported with the heating unit. The flask is heated and the solvent evaporates and moves up into the condenser where it is converted into a liquid that trickles into the extraction chamber containing the sample. The extraction chamber is designed so that when the solvent surrounding the sample exceeds a certain level it overflows and trickles back down into the boiling flask. At the end of the extraction process, which lasts a few hours, the flask containing the solvent and lipid is removed. In some device a funnel allows to recover the solvent at the end of the extraction after closing a stopcock between the funnel and the extraction chamber.

Safety cautions should be considered while using Soxhlet Extractor and Glass wares

• To prevent the introduction of contamination into the sample and sample extracts at any time during the sample processing and analytical operation, it is vital that all glassware and other materials coming into contact with the sample should be clean properly.
• All cleaned glassware should be stored prior to use under clean aluminum foil to prevent contamination by fallout from laboratory air, preferably in an enclosed cabinet.
• To prevent the introduction of contamination to the cleaned glassware preparation and subsequent handling, it is important that suitable gloves should be worn. Disposable polyethene or latex gloves have been found suitable, however powdered gloves are not acceptable.

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