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Pharmacopoeial standards applicable
to crude drugs
• Pharmacopoeial standards are set to evaluate
crude drugs in raw or powdered form. The
evaluation means determination of quality and
• Evaluation is done by comparing unknown
samples with known monographs written in
• It includes:
1. Organoleptic Evaluation
The organoleptic evaluation means the study of crude drugs
with sense organs which includes its external morphology,
colour, taste, odour, etc. Basically there are two organoleptic
It includes organised and unorganised portion of the plant.
Organised parts includes stem, roots, fruits, flowers, seeds,
leaves, herbs, etc. Unorganised parts includes resin, gums, latex,
Colour, odour and taste are sensory characters of the drugs.
e.g: clove and cinnamom gives characteristic odour
ginger and capsicum gives pungent taste
glycyrrhiza and honey are sweet
2. Microscopical Evaluation
• The crude drugs are evaluated microscopically by
their known histological characters. The shape,
size, relative position of cells and tissues,
chemical nature of cell wall and cell content are
determined. Basically following constants are
used in microscopical measurements:
a) Stomatal Number
The average number of stomata per square mm
of the epidermis is known as stomatal number.
b) Stomatal Index
The percentage proportion of the number of stomata to
the number of epidermal cells of a leaf is known as
Stomatal Index = S × 100
S= No. of stomata per unit area
E= No. of epidermal cells in the same area
c) Vein-islet number is defined as the number of vein islets
per sq. mm of the leaf surface between midrib and the
d) Vein termination number is defined as the number of
veinlet terminations per sq. mm of the leaf surface
between midrib and margin.
e) Palisade ratio is defined as the average number of
palisade cells beneath each epidermal cell.
Stomatal Number 77-115 (Lower Epidermis)
Stomatal Index 20.2-23 (Lower Epidermis)
Vein Termination Number 6.3-10.3
Palisade ratio 6-10
Vein Islet Number 2-5.5
Palisade ratio 3.7-4.2
3. Physical Evaluation
The physical parameters are determined for the
evaluation of crude drugs. It includes:
a) Moisture content
The moisture content will be determined by
heating a drug at 105°C in an oven to a constant
[Note: The excessive moisture content will
deteriorate the quality of drug by activating
enzymes and growth of micro-organisms.]
e.g: starch should contain NMT 15% moisture
b) Ash Content
The residue remaining after the incineration of
drug is the ash content of the drug.
Total ash value is determined at around 450°C
which may contain carbonates, phosphates,
oxides, silicates and silica.
Sulphated ash is determined by treating drug with
dilute sulphuric acid at around 600°C.
Acid insoluble ash is determined by treating total
ash with dilute hydrochloric acid.
e.g: Drug Total Ash % w/w
Acid insoluble ash %
Clove 7 0.75
Cannabis 15 5
c) Rf Value
Rf means the flow ratio and it is defined as the
ratio of distance covered by the solute to the
distance covered by the solvent in
d) Refractive index
Refractive index is the ratio of velocity of light
in vacuum to velocity of light in the substance.
Refractive Index = Velocity of light in vacuum
Velocity of light in substance
The value of R.I. is constant and very useful
for the standardization of Volatile and fixed
oils. It is measured by refractometer.
e.g: clove oil has refractive index 1.530-1.531
e) Optical rotation
It is the degree of rotation of plane polarized light
when it passes through an optically active
If the rotation of plane polarized light is towards
If the rotation of plane polarized light is towards
Optical rotation is determined with the help of
e.g: clove oil has optical rotation 0° to -1.5°
Dextrose (+52.7°) - Dextrorotatory
Levulose (Fructose) (-92°) - Levorotatory
f) Foreign organic matter
The parts other than the drug are known as
foreign organic matters. Its maximum limit is
given in the monographs of particular drug.
g) Extractive Value
Extract is obtained from crude drugs by
maceration or continuous extraction by soxhlet
extractor. The solvent used for the extraction
dissolves the phytochemicals present in crude
drugs like alkaloids, glycosides, tannins, resins,
etc. Solvents like alchohol, water, ether, etc are
used for extraction.
h) Volatile oil content
Volatile oil is obtained from crude drugs using
clevenger apparatus in the laboratory. Ether is used
as solvent for obtaining volatile oils.
i) Melting Point
It is the temperature required to melt down the drug.
Melting points are sharp and constant in pure
chemicals and phytochemicals.
It is the property of a liquid to resist its flow. It is
measured by using Ostwald viscometer.
4. Chemical Evaluation
Chemical evaluation of crude drugs involves
isolation, purification, identification, chemical
tests and chemical assays.
Phytochemical screening is the qualitative
chemical evaluation. It includes test for
phytochemicals like carbohydrate, protein,
alkaloids, glycosides, tannins, etc. Quantitative
chemical tests includes acid value, saponification
value, ester value, etc
e.g: Tannic acid test for alkaloids
Borntrager’s test for glycosides
5. Biological Evaluation
Biological evaluation is done to determine effect
& potency of drug in living organisms, animal
preparations or isolated living tissue. It is also
known as bioassay. It can evaluate both
pharmacological activity and toxicological activity
of a drug.
Biological evaluation is done to confirm the test
after physical and chemical test.
Biological evaluation can be:
i) Pre-clinical testing: Testing in laboratory animals
like mouse, rat, pig, dog, etc.
ii) Clinical testing: Testing in human volunteers.