Extraction

Extraction of crude drugs can be carried out by various processes, and the selection of process depends on the chemical properties of the drug’s active constituents.

Factors Affecting Choice of an Extraction Process

1) Nature of the Drug: The detailed pharmacognosy of the drug to be extracted helps in selecting the extraction process with optimum results. For extracting hard and tough drugs ( e.g., nux vomica), percolation method is used; while for soft and parenchymatous drugs ( e.g., gelatin), drugs which cannot be easily powdered ( e.g., squill), and for unorganised drugs ( e.g., benzoin), maceration method is preferred.

2) Therapeutic Value of the Drug: For extracting less therapeutically important drugs [e.g., flavours (lemon), bitters (gentian)], maceration method is used; while for drugs with significant therapeutic value ( e.g., belladonna), percolation method is preferred.

3) Stability of the Drug: For drugs whose constituents are thermolabile, continuous extraction method should be avoided.

4) Cost of Drug: For costly drugs (e.g., ginger), percolation method is used (as it is economical); while for cheaper drugs, maceration method is preferred.

5) Solvent: For drugs whose desired constituents require a solvent other than a simple boiling solvent or an azeotrope, reserved percolation method (and not continuous extraction) is used.

6) Concentration of the Product: Dilute products (like tinctures) can be prepared by maceration or percolation method. Percolation is used for preparing semi -concentrated products ( e.g., concentrated infusions) and concentrated products ( e.g., liquid extracts or dry extracts). In case the solvent is suitable and the desired constituents are heat-stable, a continuous extraction method is used

• Menstrum: Solvent or mixture of solvent used for extraction.

• Miscella: Solution with extracted substance.

• Rinsing: Dissolution of extractive substance out of the disintegrated cell.

• Lixative or leaching: Water is used as a solvent for extraction.

• Marc: Residue left after extracting the desired constituents.

Various extraction methods employed are:

1. Infusion

2. Decoction

3. Maceration,

4. Digestion,

5. Percolation,

6. Continuous hot extraction (Soxhlet extraction),

7. Supercritical fluid extraction,

8. Counter current extraction,

9. Microwave assisted extraction,

10. Ultrasonic assisted extraction,

11. Pressure cooker extraction,

12. Extraction by passage through a colloid mill,

13. Use of surface active agents in drug extraction, and

14. Expression and diacolation.