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Soxhlet Extraction/Continuous Hot Percolation Process:
This extraction process is more suitable where menstrum have less penetration into the cellular tissue.
Active constituent are not readily extracted with solvent.
The quantity of solvent for extraction of the active constituents is very less.
Soxhlet extraction is preferable in above mentioned conditions.
Here the hot menstrum cycle is passed again and again over the crude drug and solubilize its active ingredient until the drug become exhausted.
The apparatus consist of three important parts:
(a) A round bottom flask (RBF) which contain menstrum.
(b) Extraction chamber in which drug is kept in thimble.
(c) Condenser.
The size reduction of the crude drug was performed and packed the size reduced drug was into the thimble (made of filter paper or cellulose) which is helpful to prevent choking of the extractor.
Place the solvent in the round bottom flask (RBF) and boiled it by heating mantle.
The vapour of the solvent goes to the condenser via side tube.
The condenser condenses the vapour of solvent and this solvent penetrates the packed drug.
It percolates the crude drug and extracted the active ingredient.
The level of menstrum is increased in the extractor until it reaches to maximum point from where it is siphoned into the round bottom flask.
This menstrum is again heated in RBF where active constituent remains in RBF and vaporized solvent again pass through the side tube and condenser which penetrates the drug present in the extractor.
The process will continue till the drug become exhausted.
Some drug-like resin, opium, gum blocks the Soxhlet apparatus so this is not a suitable method for these drugs.
Thermolabile drugs and constituents are not suitably extracted by this method because the active ingredient can be destroyed.
Pure solvent or only those solvent mixtures which have constant boiling temperature can be used for extraction purposes.
This process has the following limitations:
1) It is not suitable for drugs having thermolabile active constituents, e.g., enzymes, alkaloids, anthraquinone derivatives, esters, etc., because this extraction process requires a high temperature and also the extract in the flask is maintained in hot conditions during the entire process.
2) It is suitable only for pure solvents, constant boiling mixtures (like alcohol- water), or solvent mixture forming azeotropes.
3) If the menstruum is an ordinary binary mixture, the vapour composition and the liquid composition will be different.
4) It is not used if the drug to be extracted is of such physical nature that it would block the Soxhlet apparatus, e.g., opium, gum, resin, orange peel, etc.
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