Table of Contents
Advantages of Soxhlet extraction
Disadvantages of Soxhlet extraction
Automated Soxhlet Extraction
Comparison of different Soxhlet extraction modifications
Modern Day Applications
Extraction is a process in which a substance is removed from a solid, a liquid or a gas using
an extractant. The extraction material is the material from which the substance is to be
removed. At the end of the extraction, we get the desired substance and the raffinate from
which the substance was removed.
The extractant cannot be any arbitrary solvent. It should only remove the desired material in
significant amount from the extraction material and must not chemically react with other
materials contained in the extraction material. So The polarity of the solvent should be similar
to that of the target analytes. This condition provides sufficient contact with analytes, which
governs extraction recovery.
Extraction is often used as a purification method when distillation or rectification cannot be
Soxhlet extraction process is also an extraction process that can remove sparingly soluble
substances from solids by means of a solvent. Originally, this method was introduced by
Franz von Soxhlet in 1879 for determining the fat content in foods.
Parts of Apparatus
1. Stirrer bar
2. Still pot
3. Distillation path
6. Siphon top
7. Siphon exit
8. Expansion adapter
10. Cooling water in
11. Cooling water out
In this method the solvent is placed in a flask and is heated to boiling
point. Then, solvent vapours rise in the entire apparatus and
condense at a coil condenser. From here, the solvent drips onto a
cellulose extraction thimble that sits in the Soxhlet extractor and
which is filled with the extraction material. The extractant thus drips
directly onto the extraction material and collects in the Soxhlet
When a critical liquid level is reached, the Soxhlet extractor abruptly
drains into the flask. This process is also called siphoning and is
driven by way of a suction lifting effect. In the flask, the solvent has
now been distilled from the extract and can thus remove new extract
from the extraction material.
Standard Operating Procedures (SOP)
The drug to be extracted is packed in a paper cylinder made from a filter paper and it is
placed in the body of soxhlet extractor.
The solvent is placed in the flask and the apparatus is fitted.
A condenser unit is attached with the extraction tube.
The flask containing solvent is heated and it starts to evaporate
These vapour enters into the condenser through side tube to get condensed into a hot
liquid which falls on the column of the drug.
When extractor gets filled with solvent, the level of syphon tube also raises upto its top.
The solvent containing active constituent of the drug in the syphon tube, syphon over
flow and run into the flask, thus emptying the body of the extractor.
The soluble active constituent of the drug remain in the flask while the solvent is
repeatedly volatilised.This process of filling and emptying of extractor is repeated until the
drug is exhausted , almost for 15 times for complete exhaustion of drug.
Discontinue the process and clean the extraction tube and thimble.
Advantages of Soxhlet extraction:
Conventional Soxhlet extraction has some very important advantages:
the transfer equilibrium is readily displaced because of the repeated contact between the
sample and fresh portions of solvent.
the heating of the distillation flask provides a relatively high temperature during the whole
the methodology is simple – very little specialized training is required.
no filtration is required after leaching.
the apparatus is simple and inexpensive.
simultaneous extraction in parallel is possible, sample throughput can be increased.
extraction of analytes can be performed from a larger sample mass in comparison with the
other techniques for extraction of solid samples.
a wide range of compounds can be extracted from different solid matrices.
many current official analytical methods are based on this standard technique.
Disadvantages of Soxhlet extraction:
However, Soxhlet extraction also has some significant drawbacks:
the extraction time is long (up to 48 hours).
large amounts of solvent are used, so there is the problem of proper waste disposal.
analytes may decompose thermally during the long extraction process.
an evaporation/concentration step is required after extraction.
selectivity of extraction is limited to solvent selectivity.
Despite these many disadvantages, however, Soxhlet extraction is still a benchmark technique
with which the performance of other leaching techniques is compared. That is why much effort
has been expended to overcome these difficulties.
Automated Soxhlet Extraction - the
• In the early 1970s, Randall developed an accelerated
extraction technique, sometimes called the submersion
technique, which was a milestone in this field. Randall’s
approach has led to a significant reduction in leaching
time. Moreover, it is fully compatible with classical Soxhlet
extraction, and precision is much better in comparison
with the traditional approach.
• Unlike classical Soxhlet extraction, the sample is totally
immersed in boiling solvent. This simple modification
provided the opportunity to shorten the extraction time,
because analytes are more soluble in hot solvent than in
the cold-to-warm (not boiling) solvent used in the
classical Soxhlet method.
• Randall’s procedure consists of three stages: boiling,
rinsing and evaporation/solvent recovery
Diagram of the Randall extractor (left)
compared with the conventional Soxhlet
The main applications concerning the extraction of soluble matter from different kinds of samples
by means of automated systems are:
• cereals and cereal products;
• milk and dairy products;
• meat products;
• chocolate and cocoa products;
• oil and oilseed products;
• fat in food;
• lipids in eggs and egg products;
• pesticides, phenols, PCBs, dioxins, PAHs,
• coating of fertilizers,
• colorants on textile fibers;
• paper pulp;
• softeners and additives in plastics and