Physical Separation Method

Fractional Methods in Pharmacognosy

1. Fractional Crystallization

• Principle: Separation based on different solubilities of compounds at different temperatures.

  • Less soluble compounds crystallize first when cooling.

  • Can be repeated to increase purity.

• Use: Purifies compounds from plant extracts (e.g., isolating crystalline natural products).

2. Fractional Distillation

• Principle: Separation based on different boiling points.

  • In a fractionating column → vaporization & condensation happen repeatedly.

  • Compounds with lower boiling points come out first.

• Use: Isolates volatile compounds like essential oils; separates liquids with close boiling points.

3. Fractional Liberation

• Principle: Separation based on alkaloid basicity (pH control method).

  • Step 1: Acidify → alkaloids become salts (water-soluble).

  • Step 2: Extract weak alkaloids with organic solvent.

  • Step 3: Slowly add base (like ammonia) → alkaloids precipitate step by step according to their basicity.

  • Step 4: Collect fractions → separates alkaloids one by one.

• Use: Special method for separating alkaloids from plant mixtures.

👉 Memory Trick:

• Crystallization = Solubility (cold makes crystals form)

• Distillation = Boiling points (heat & vapor)

• Liberation = pH stepwise release (alkaloids)