TO study the working and the principles of Soxhlet apparatus in the extraction of crude Drugs.

This is a experiment-2 of pharmacognosy and phytochemistry-2, B.pharm, 5th sem.


TO study the working and the principles of Soxhlet apparatus in the extraction of crude Drugs.


DR. Chakraborty Anup K, “A practical textbook of pharmacognosy and Phytochemistry-2”, edition-2019, P.V Publications, pages no 166-173


Soxhlet Apparatus


Extraction is a process in which the physical separation of soluble phytoconstituents takes place which is available in a non-soluble plant matrix. This process of solubilization takes place with the help of water or with the help of polar to non-polar organic solvents. This solvent is known as menstruum whereas the solution containing the extracted phytoconstituents is known as miscella.

Types of Extraction:

  • (1) Solid Extraction: The term ‘solid extraction’ refers to the extraction of solid from solid by using the appropriate solvent. This type of extraction needs to be performed before any further separation or processing.
  • (2) Solvent Extraction: The term ‘solvent extraction’ refers to a process in which phytoconstituents that are extracted by the solid extraction process are partitioned between any two immiscible solvents. Ideally, this process needs to be carried out after the solid extraction process and it is considered a purification process. On a laboratory scale solvent extraction is carried out in a separating funnel.

Mechanism of Extraction

Solid extraction by using the appropriate solvent, is the most preferred method for the extraction of phytoconstituents from the plant material. In this case, initially solvent penetrates the solid matrix, then the solubilization of solutes in the solvent takes place. Later on, the solute diffuses out of the solid matrix and finally extracted solutes are separated by solvent evaporation.

The following factors are responsible for the extraction efficiency of the solvent:

  • (1) the nature of extracting solvent
  • (2) particle size of the raw material
  • (3) ratio of solvent to plant material
  • (4) temperature at which extraction is carried out and
  • (5) duration of extraction

Soxhlet Apparatus

A Soxhlet extractor is a laboratory apparatus that was invented in 1879 by Franz von Soxhlet. It was originally designed for the extraction of a lipid from a solid material. This procedure is used typically with pure organic solvents. A typical soxhlet apparatus is shown below. 

Soxhlet apparatus
Soxhlet apparatus

Working of Soxhlet Apparatus

The material to be extracted is first coarsely powdered and then placed inside the thimble. The drug may be suitably packed in filter paper or kept as such. In the latter case, a thin layer of cotton should be placed at the bottom of the thimble to avoid the entry of drug particles into the siphon tube. The top layer of the drug is also covered with a thin layer of cotton to avoid the disturbance of the drug when added from the top. A portion of the apparatus forming together with a side tube, thimble, and siphon tube is called a soxhlet extractor. Once the drug is filled into the extraction thimble, the soxhlet extractor is placed onto the round bottom flask. From the top of the extractor, the extraction solvent (menstruum) is added slowly with the aid of a glass rod. Once the solvent reaches the top of the siphon tube, it gets siphoned back to the round bottom flask. The volume of solvent used is generally 3 to 4 times the volume of a thimble. Once the complete solvent is

transferred to the round bottom flask, the condenser is fixed as shown in the figure along with the water inlet and outlet. The cold water tap is opened and is allowed to circulate in the condenser. The whole assembly is set on the heating mantle and the mantle is switched on.

Once the solvent begins to boil, the solvent vapor travels to the condenser and falls into the thimble in the form of a hot liquid. The thimble containing the drug slowly begins to fill with hot extracting solvent thereby initiating the process of extraction. When the thimble is almost full, it gets emptied into the round bottom flask through the siphon tube. This cycle is repeated several times until all the desired phytoconstituents are extracted. During each cycle, pure hot solvent dissolved some of the phytoconstituents and siphoned back to the round bottom flask.

During each cycle, a portion of the non-volatile compound dissolves in the solvent. After cycles, the desired compound is concentrated in the distillation flask.

Advantages of Soxhlet Extraction

  • 1. The process is automatic and continuous.
  • 2. This system uses the same portion of solvent repeatedly which is being passed through the sample every time. Thus, the process saves solvent by recycling it over the sample.
  • 3. Process is time-saving. To prepare the extract of about 500 g of drug, the duration required is less than 24 hrs.
  • 4. Process is useful for exhaustive extraction of plant material with specific solvent, for example, defatting of plant material is done by using petroleum ether as a solvent.
  • 5. To prepare a series of exhaustive extracts with solvents of increasing polarity (e.g. petroleum ether, chloroform, and ethanol), this is the best suitable method.

Disadvantages of Soxhlet Extraction

  • 1. In this process, the extracted phytoconstituents in the round bottom flask are continuously boiled along with the solvent. This may produce a detrimental effect on thermo labile phytoconstituents.
  • 2. The total amount of certain substances extracted will exceed their solubility in that particular solvent. Because of this, such types of constituents may precipitate out in the lower container and will require a higher volume of solvent for subsequent dissolution.
  • 3. Method is not suitable for solvents with a high boiling point like water, since the whole apparatus below the condenser needs to be at this temperature for effective movement of solvent vapor.
  • 4. Method can be used either with pure organic solvents or with azeotropic mixtures and cannot be used for extraction with any solvent mixture, for example, hexane: dichloromethane (1:1).  


The working and principal of the Soxhlet apparatus in the extraction of crude Drugs were studied.

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