11. EXTRACTION

Extraction is one of the most important unit operations in pharmaceutics and pharmacognosy.
It is the process used to separate active constituents (such as alkaloids, glycosides, flavonoids, or oils) from crude drugs or natural sources using suitable solvents.

Extraction helps in isolating therapeutically active compounds while removing unwanted or inert materials, ensuring a pure, potent, and stable pharmaceutical preparation.

Definition

Extraction is the process of isolating active ingredients from raw materials of plant or animal origin (or directly from natural sources) using selective solvents called menstruum.

ORIGINAL NOTES:

Objectives of Extraction

• To obtain desired active constituents in pure form.
• To remove impurities or inert materials from crude drugs.
• To obtain standardized extracts for formulation of various dosage forms.
• To ensure maximum yield of bioactive compounds with minimal degradation.
• To produce extracts that are safe, stable, and therapeutically effective.

Classification of Extraction

Extraction processes are generally classified based on the physical state of material and method used, as follows:

1. Liquid–Liquid Extraction (Solvent Extraction)

• Used when both feed and solvent are in liquid phase.
• The solute is transferred from one liquid (feed) to another immiscible solvent based on its distribution coefficient.
• Commonly used to extract aromatic or bioactive compounds from plant extracts.
• Example: Extraction of caffeine from tea or coffee.

2. Solid–Liquid Extraction (Leaching)

• In this process, soluble constituents are removed from a solid using a liquid solvent.
• The solvent dissolves the desired components, leaving behind the insoluble residue (marc).
• Example: Extraction of glycosides from plant roots and barks.

3. Solid Phase Extraction (SPE)

• Used mainly in analytical and purification processes.
• Involves adsorption of solutes from a liquid onto a solid phase, followed by elution.
• Common in pharmaceutical quality control laboratories for purification and sample concentration.

Methods of Extraction

Several techniques are used to extract active ingredients from natural materials. The choice of method depends on solvent type, nature of the plant, temperature, and desired product.

1. Maceration

• Crude drug is soaked in a closed vessel with solvent at room temperature for 3 days with occasional stirring.
• The mixture is filtered, and the liquid extract (menstruum) is collected.
• Example: Preparation of tinctures and extracts.

2. Percolation

• The most commonly used method for large-scale extraction.
• Drug is packed in a percolator, moistened with solvent, and allowed to stand for 24 hours.
• Solvent is then added continuously to obtain the extract by slow percolation.
• Used in the preparation of fluid extracts and tinctures.

3. Decoction

• Involves boiling the crude drug in water for a fixed time and then filtering it.
• Suitable for heat-stable, water-soluble compounds found in hard plant parts like roots and barks.
• Example: Herbal decoctions in traditional systems of medicine.

4. Digestion

• A modified maceration process carried out with gentle heat to enhance solvent penetration.
• Used for extraction of constituents requiring moderate heating.

5. Infusion

• A simple and quick method where the crude drug is soaked in cold or boiling water for a short period.
• Produces dilute extracts known as infusions.
• Example: Herbal teas or medicinal infusions.

6. Soxhlet Extraction (Hot Continuous Extraction)

• Commonly used for lipid and plant compound extraction.
• The sample is placed in a thimble inside a Soxhlet apparatus, and the solvent is repeatedly vaporized, condensed, and siphoned.
• Ensures complete extraction with minimal solvent usage.

7. Microwave-Assisted Extraction (MAE)

• Uses microwave energy to heat the solvent and plant material.
• Microwaves disrupt cell walls and improve mass transfer, resulting in fast and efficient extraction.

8. Sonication Extraction

• Uses ultrasound waves (20–2000 kHz) to create cavitation, improving solvent penetration and extraction rate.
• Simple, energy-efficient, and suitable for both small and large-scale processes.

9. Accelerated Solvent Extraction (ASE)

• Automated, high-pressure, and high-temperature extraction technique.
• Uses less solvent and time compared to traditional methods.
• Common in pharmaceutical and food analysis.

10. Supercritical Fluid Extraction (SFE)

• Uses supercritical CO₂ (above 31.1 °C and 73.8 bar) as the solvent.
• Efficient for non-polar compounds; addition of small polar solvents improves polarity range.
• Produces pure, solvent-free extracts ideal for pharmaceuticals and nutraceuticals.

Applications of Extraction

1. Isolation of active constituents like alkaloids, glycosides, tannins, and essential oils.
2. Production of standardized herbal extracts for medicines and cosmetics.
3. Separation and purification of proteins, enzymes, and antibiotics.
4. Recovery of high-boiling or sensitive compounds from complex mixtures.
5. Used in chemical and food industries for flavor and fragrance extraction.
6. Extraction of fixed oils and essential oils from plant seeds and flowers.
7. Isolation of hormones and biological products such as insulin and gelatin.