Introduction
Microscopical and powder microscopical studies are important methods used in pharmacognosy for the identification and quality control of crude drugs. These techniques help detect adulteration, understand the structure of plant tissues and confirm the authenticity of raw plant material. When a crude drug is available as a whole plant part, microscopical study is performed on sections. When it is in powdered form, powder microscopy becomes the preferred method.
Need for Microscopical Study
- To identify crude drugs based on internal structure.
- To detect adulterants and substitutes.
- To understand arrangement of tissues such as epidermis, cortex and vascular bundles.
- To study cell contents like calcium oxalate crystals, starch grains, fibres and trichomes.
- To support pharmacognostic evaluation along with chemical and physical methods.
Microscopical Study of Crude Drugs
This involves studying thin sections of plant parts under a microscope. The aim is to observe tissues, internal arrangements and diagnostic characters.
Steps in Microscopical Examination
- Select a representative sample of the crude drug.
- Prepare thin transverse or longitudinal sections.
- Clear the section using reagents like chloral hydrate.
- Stain the section to highlight different tissues.
- Mount the sample permanently or temporarily.
- Observe under the microscope and identify diagnostic structures.
Common Staining Reagents
- Phloroglucinol + HCl: Stains lignified tissues red.
- Safranin: Stains nuclei and lignified walls.
- Iodine solution: Stains starch grains blue.
- Sudan III / IV: Stains oils and fats orange-red.
- Fast green: Counterstain for cellulose.
Tissues Commonly Examined
- Epidermis: With or without cuticle, containing trichomes and stomata.
- Cortex: Parenchyma, collenchyma, sclerenchyma.
- Vascular bundles: Arrangement of xylem, phloem and cambium.
- Medullary rays: Radiating lines between vascular bundles.
- Secretory structures: Oil glands, resin ducts.
Powder Microscopy
Powder microscopy is done when the crude drug is available in powdered form. Since macroscopic identification is not possible, we depend entirely on microscopic characters. These include fragments of tissues, special cell contents and unique diagnostic features.
Procedure for Powder Microscopy
- Take a small amount of the powder on a slide.
- Add suitable reagents such as chloral hydrate for clearing.
- Add required stains depending on the expected constituents.
- Mount with glycerin or water.
- Examine under low and high magnification.
Diagnostic Characters Studied in Powder Microscopy
1. Epidermal Cells
Presence of epidermal cells with cuticle, shape of anticlinal walls and nature of stomata help in drug identification. Stomatal type (e.g., anisocytic, paracytic, diacytic) is a stable characteristic useful for authentication.
2. Trichomes
Hair-like outgrowths from epidermis. They vary in structure and are useful for diagnosis.
- Unicellular or multicellular
- Glandular or non-glandular
- Simple, branched or stellate
3. Fibres
Lignified fibres appear long with tapering ends. They stain red with phloroglucinol. Presence of fibres is characteristic in many crude drugs like cinnamon and ginger.
4. Calcium Oxalate Crystals
Crystals appear in shapes like prisms, rosettes, needles and sandy forms. Their size and form help identify drugs and detect adulteration.
5. Starch Grains
Starch grains differ in shape, size and hilum type. They stain blue with iodine and are common in drugs like potato, ginger, and ipecac.
6. Vessels
Fragments of xylem vessels show spiral, annular, scalariform or pitted thickenings. These patterns are highly diagnostic.
7. Cork Cells
Polygonal, brownish cells found in barks and roots. They indicate the presence of bark fragments.
8. Secretory Cells
Droplets from oil glands, resin ducts or mucilage ducts help identify aromatic and resinous drugs.
Importance of Microscopical and Powder Microscopy in Crude Drug Evaluation
- Confirms identity when macroscopic features are absent.
- Helps detect mixing of inferior plant material.
- Essential for powdered market samples where adulteration is common.
- Gives permanent diagnostic characters unaffected by drying or storage.
- Supports chemical and physical testing for complete quality control.
Limitations
- Does not provide information on chemical composition.
- Requires skill and experience to interpret structures correctly.
- Powdered drugs may lose some original structures.
Detailed Notes:
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