Factors affecting extraction, Pharmacognosy, crude drugs extraction factors, Factors affecting choice of Extraction Process Factors considered when selecting a solvent

1. Factors affecting choice of Extraction Process
Factors considered when selecting a solvent
Extraction
By,
M. S. Divya Sree,
Assistant Professor,
Department of Pharmacognosy

2. Factors affecting choice of Extraction Process
1. Character of drug:-
 The knowledge of pharmacognosy of the drug is essential to
select the right method of extraction process.
 The maceration process is used when the drug is soft,
unorganised, unpowderable and to avoid powdering of it.
 The percolation process is used when the drug is hard and
tough.

3. 2. Therapeutic value of the drug:-
o When the drug has considerable therapeutic value, the
maximum extraction is required.
o So the percolation process is used e.g . Belladonna.
o In case the drug has little therapeutic value, the
efficiency of extraction is unimportant and maceration
process can be used to extract the drug.

4. 3. Cost of drug:-
 The costly drugs are extracted by using the percolation
process, whereas cheap drugs are extracted by maceration
process.
4. Stability of drug:-
 Continuous hot extraction process should be avoided when
the constituents of the drug are thermolabile in nature.
In that case maceration or percolation process may be used
to extract the active constituents of the drug.

5. 5. Solvent:-
 If water is used as a solvent the maceration process should
be recommended.
The percolation process should be preferred if non-aqueous
solvents used for extraction.
If the desired active constituents of drug demand a solvent
other than a pure boiling solvent or an azeotrope, continuous
hot extraction process should be avoided and percolation
process may be used.

6. 6. Concentration of product:-
 The dilute products such as tinctures can be made by
using maceration or percolation process.
 For semi-concentrated preparations, such as concentrated
infusions, double or triple maceration process can be used.
 The liquid extracts or dry extracts which are concentrated
preparations are prepared by using percolation process.

7. Factors considered when selecting a solvent
1) Solvent power (selectivity).
Only the active, desired constituents should be extracted
from the plant material, which means that a high
selectivity is required.
2) Boiling temperature.
The boiling point of the solvent should be as low as
possible in order to facilitate removal of the solvent from
the product.

8. 3) Reactivity.
The solvent should not react chemically with the extract,
nor should it readily decompose.
4) Viscosity.
A low viscosity of the solvent leads to low pressure drop
and good heat and mass transfer.
5) Safety.
The solvent should be non-flammable and non-corrosive,
and should not present a toxic hazard; its disposal should not
imperil the environment.

9. 6) Cost.
The solvent should be readily available at low cost.
7) Vapor pressure.
To prevent loss of solvent by evaporation, a
low vapor pressure at operating temperature is required.
8) Recovery.
The solvent has to be separated easily from the
extract to produce a solvent-free extract.