Pharmacognosy · Short notes

Crude Drug Evaluation: Short Notes & Cheat Sheet

Organoleptic, microscopic, physical, chemical and biological evaluation of crude drugs, quantitative microscopy and adulteration.

Short notes

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In practice several methods are combined; identity is usually settled by microscopy and chemical tests.

Evaluation confirms identity, checks quality and purity, and detects adulteration.
Organoleptic evaluation uses the senses: colour, odour, taste, size, shape and fracture.
Microscopic evaluation looks at cell types, stomata, trichomes and calcium oxalate crystals.
Chemical evaluation uses identification tests and assays (TLC fingerprinting, HPLC). Biological evaluation (bioassay) is used when chemical methods are inadequate.

Stomatal types: anomocytic (irregular cells), anisocytic (three unequal subsidiary cells), diacytic (two cells at right angles; mint) and paracytic (cells parallel to the pore; senna).
Calcium oxalate crystals: rosettes (clusters), prisms (senna), raphides (needle bundles in squill and ipecac) and microsphenoidal sandy crystals (belladonna).
Stomatal index = S / (E + S) × 100, where S is the number of stomata and E the number of epidermal cells in the same area.
Other leaf constants: stomatal number, palisade ratio, vein-islet number and vein termination number.
The lycopodium spore method measures the proportion of a powdered drug quantitatively.

Moisture content is found by loss on drying, or by toluene distillation for drugs containing volatile oil.
Total ash shows inorganic matter. Acid-insoluble ash shows sand and silica (earthy contamination). Water-soluble ash is also measured.
Extractive values (water- or alcohol-soluble) help detect exhausted drugs.
Other values: swelling index (ispaghula), foaming index (saponins), bitterness value, volatile oil content (Clevenger apparatus) and fluorescence under UV.

Types: substitution with inferior or exhausted drug, artificial imitations, adding worthless material, and deterioration from poor storage.
Examples: papaya seeds mixed with black pepper, safflower or corn silk with saffron, and exhausted clove or ginger (oil already removed).
Pharmacopoeias usually limit foreign organic matter to about 2%.

High-yield facts in one place. Cover the right-hand column and test yourself.

Feature	Example drug
Paracytic stomata	Senna, coca
Diacytic stomata	Peppermint (Lamiaceae)
Anisocytic stomata	Belladonna, Datura (with anomocytic)
Raphides	Squill, ipecacuanha
Prisms	Senna
Microsphenoidal crystals	Belladonna

Value	Detects
Acid-insoluble ash	Sand, earth, silica
Extractive value	Exhausted or poor-quality drug
Moisture content	Risk of mould and hydrolysis
Swelling index	Quality of mucilage drugs
Foaming index	Saponin content
Vein-islet number	Distinguishes related leaves

Acid-insoluble ash = Sand: Silica and sand do not dissolve in acid, so this value shows earthy contamination.

Toluene distillation, not simple loss on drying, is used for moisture in drugs with volatile oil.
The stomatal index is more constant for a species than the stomatal number.
Senna has paracytic stomata; peppermint has diacytic stomata.
Exhausted drugs look normal but have low extractive values.

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