Extraction of Alkaloids
By
Dr.Mukul Tailang
Professor
School of Studies in Pharmaceutical Sciences
JIWAJI UNIVERSITY
GWALIOR (M.P.)
Extraction of Alkaloids
Alkaloids occur in plants usually in mixtures of
related compounds together with inert
constituents, such as tannins, proteins, fats,
resins, and pigments, which generally hinder their
isolation.
Procedures adopted for isolation of alkaloids
include the major following steps:
preparation of the plant sample
liberation and extraction of the free alkaloidal
bases
purification and fractionation of the crude
extract
isolation of individual alkaloids.
Preparation of the plant sample
The collected plant material is
carefully
dried,
reduced to a suitable size and,
if necessary, defatted with petroleum ether
(e.g. in case of seeds).
Although most alkaloids are insoluble
in petroleum ether, yet the extract
should be tested before rejection.
Extraction & purification
For extraction of alkaloids, one of the following
methods are applied:
Method I:
1. The powder is treated with lime water, that liberates
the free bases if present as salts, and combines with
acids, tannins or other phenolics.
2. The alkaline extract is then shaken with a suitable
organic solvent, generally chloroform.
3. The organic layer is separated and concentrated
(containing free alkaloids and lipophilic impurities).
4. The concentrated organic extract is then shaken with
aqueous acid and allowed to separate.
5. This separates alkaloids as their salts (in the aqueous
layer) from most other impurities, which remain in the
organic layer (purification).
Extraction & purification
Method II:
1. The powdered material is extracted with
water or aqueous alcohol containing
dilute acid.
2. Alkaloids are extracted as their salts
together with accompanying soluble
impurities.
3. The acidic extract is shaken with
chloroform or other suitable organic
solvent to remove pigments and other
undesirable impurities (weak bases
may be present).
Liberation and extraction of
alkaloidal bases:
The acid extracts (alkaloidal salts)
resulting from either methods I or II
are treated with dilute alkali
generally sodium bicarbonate or
ammonia to liberate the free bases
These free bases are separated by
filtration or extraction with organic
solvents.
Separation of individual alkaloids
Separation could be carried by:
Fractional precipitation or crystallization:
This is generally performed after derivatization to
salts such as oxalates, tartrates and picrates.
Gradient pH extraction:
This method is suitable for separating alkaloids of
different basicity (weakly, moderately and strongly
basic).
The crude mixture is dissolved in 2% tartaric acid
and extracted with organic solvent.
The pH of the aqueous solution is gradually
increased to pH 9,
after each increment in pH, it is extracted with
organic solvent.
Chromatographic techniques:
These are the most suitable in case of complex
mixtures.
