Simple methods for isolation and purification of natural bioactive compounds

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2. Physical techniques are also used for separating and
purifying the plant constituents
a) Fractional crystallization
b) Fractional liberation
c) Steam distillation
e) Fractional distillation
f ) Sublimation

3. FRACTIONAL CRYSTALLIZATION
Crystallization is an old but an important method for the
purification of compounds from the mixture
Crystallization mostly depends upon the inherent
character of the compound which form the crystals at the
point of super- saturation in solvent in which it is soluble.

4. Compounds such as Sugars, Glycosides, Steroids,
Triterpenoids, Flavonoids etc., show crystalline nature
with certain exceptions

5. METHODS OF CRYSTALLIZATION
1. Concentration 2. Slow evaporation 3. Refrigeration
Based on differences in solubility of the components of
a mixture in a particular solvents .
Valuable for resolution of often otherwise intractable mixtures
Eg: Picrates of alkaloids , Osazone of sugars are isolated by
this method

6. SUBLIMATION
The method of purification by the sublimation
process consists of placing the impure compound in a
dish covering it with a piece of perforated paper and
placing an inverted funnel

7. The stem of the funnel is plugged with cotton wool and the
sides of the funnel kept cooled.
Now the dish is heated gently over a sand bath where by
the compound sublimes and gets deposited on the inner
cooled surface of the funnel , leaving non-volatile
impurities in the dish.

8. The perforated filter paper allows the vapour to go into
the funnel but checks the condensed sublimate from
falling back into the dish.

9. Applications :
1. Isolation of caffeine from tea
2. Purification of materials present in the crude drug

10. FRACTIONAL LIBERATION
Eg - a mixture of alkaloid salts in aqueous solution,
when treated with aliquots of alkali gives first the
weakest base in the free state followed by base
liberation in ascending order of basicity .

11. If the mixture is shaken with organic solvent after each
addition of aliquot of a alkali, a fractional series of bases
shall be obtained.

12. STEAM DISTILLATION
Used for the extraction of volatile oils and hydrocyanic
acid from plant material
FRACTIONAL DISTILLATION
Used for the separation of components of volatile oils

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