An emulsion is a biphasic liquid preparation containing two
immiscible liquids, one of which is dispersed as minute
globules into the other.
The liquid which is converted into minute globules is called the
dispersed phase' and the liquid in which the globules are dispersed
is called the continuous phase.
The globule size in emulsion varies from 0.25 to 25 um diameter
3. TYPES OF EMULSIONS
The emulsions are of two types:
Oil in water type (o/w)
Water in oil type (w/o)
In oil-in-water type emulsion, the oil is in dispersed phase whereas
water is in the continuous phase.
The o/w type emulsions are preferred for internal use.
In these emulsions, gum acacia, tragacanth, methyl cellulose,
saponins, synthetic substances and soaps formed from monovalent
bases like Na+, K+ and NH₂ are used as an emulsifying agents.
4. In water-in-oil type emulsion, the water is in the dispersed phase
whereas oil is in the continuous phase.
The wool fat, resins, beeswax and soaps from divalent bases like Ca,
Mg and Zinc are used as an emulsifying agents.
The w/o type emulsions are mainly used externally as lotions or creams.
5. Dilution test
The emulsion is diluted with water. In case the emulsion remains
stable after its dilution, it is o/w emulsion. The w/o emulsion breaks on
its dilution with water but remains stable when diluted with oil.
TESTS FOR IDENTIFICATION OF TYPE OF EMULSION
6. DYE TEST
The scarlet red dye is mixed with the emulsion. Place a drop of the
emulsion on a microscopic slide, cover it with a cover-slip, and examine it
under a microscope. If the disperse globules appear red and the ground
colorless, the emulsion is o/w type. The reverse condition occurs in w/o
type emulsion i.e., the disperse globules appear colorless in the red
Certain fixed oils possess the physical property of fluorescing in the
presence of ultraviolet radiation. On microscopic observation of emulsion
under ultraviolet radiation, the whole fluorescence indicates that oil is
present in continuous phase (w/o emulsion) ant droplets fluorescence
indicates that oil is present in dispersed phase (o/w type emulsion).
7. CONDUCTIVITY TEST
Water is a good conductor of electricity, whereas oil is non-conductor
of electricity. The conductivity test can be performed by dipping a pair
of electrodes connected through a low voltage bulb in the emulsion. If
the bulb glows on passing the electric current, the emulsion is o/w
type, because water is in the continuous phase. In case the bulb does
not glow, the emulsion is w/o type, because oil is in the continuous
8. Classification of emulsions in accordance to the type of emulsifying agent
used in the preparation of an emulsion
Emulsion containing natural gum: e.g gum acacia, tragacanth and mucilage of Irish moss.
Emulsion containing gum substitute e.g., cellulose and its derivatives and salts of alginic
Emulsion containing various soaps.
Emulsion containing saponins.
Emulsion containing starch.
Emulsion containing natural waxes e.g., wool fat and beeswax.
Emulsion containing synthetic waxes e.g., emulsifying wax and cetomacrogol emulsifying
Emulsion containing other emulsifying agent such as gelatin and lecithins. pectin, egg
CLASSIFICATION OF EMULSION
9. Classification of emulsions in accordance to their mode of
Emulsions for oral administration: e.g., castor oil, olive oil, almond oil,
cod-liver oil and liquid paraffin.
Emulsions for external use:
Emulsions for parenteral use: vitamins such as A, D, E and oil soluble
Emulsions for rectal use: e.g. Pectin, egg yolk, gelatin and lecithin
10. Emulsifying Agents
Preservation of Emulsions
The emulsifying agents reduce the interfacial tension between two
phases i.e. oily phase and aqueous phase and thus make them
miscible with each other and form a stable emulsion.
Emulsifying agents are also known as emulgents or emulsifiers.
FORMULATION OF EMULSION
11. HLB METHOD
Griffin devised a useful method for calculating balanced mixtures of
emulsifying agents to provide a particular type of emulsion. It is
called the Hydrophilic Lipophilic balance or HLB method.
Every emulsifying agent is given a number on HLB scale, which is
divided into 18 units.
Emulgents with higher numbers (8-18) indicates hydrophilic
properties and produces o/w type emulsions.
Emulgents with lower numbers (3-6) represents lipophilic properties
and produces w/o type emulsions.
12. The following table indicates the HLB values and applications of
13. An ideal emulsifying agent should possess the following
It should be capable of reducing the interfacial tension between the
two immiscible liquids.
It should be compatible with other ingredients of the preparation.
It should be non-toxic.
It should be capable to produce and maintain the required
consistency of the emulsion.
It should be chemically stable.
It should be capable of keeping the globules of dispersion liquid
15. Natural emulsifying agents from vegetable sources:
These are carbohydrates which includes gums and mucilaginous
substances. They are anionic in nature and produce o/w type
Acacia: Acacia is considered to be the best emulsifying agent for
the preparation of emulsion for internal use.
Name of the oil oil Gum
Fixed oil 4 1
Volatile oil 2 1
Mineral oil 3 1
16. Tragacanth: Tragacanth alone is rarely used as an emulsifying
agent because it produces very coarse and thick emulsion.
Agar: It is not a good emulsifying agent, as it forms a very coarse
and viscous emulsion.
Starch: Starch mucilage is rarely used because it forms very coarse
emulsions. It is generally used to prepare enemas.
Natural emulsifying agents from animal sources:
Wool fat: It is generally used in emulsion which are meant for
external use. It produces o/w type emulsions.
Egg yolk: It is mainly used in extemporaneous preparations meant
for internal use
17. Semi-synthetic polysaccharides:
Methyl cellulose: It is a synthetic derivative cellulose.
It is widely used as suspending, thickening and emulsifying agent.
Sodium carboxy methyl cellulose: It is used as an emulsion
stabilizer in the concentration of 0.5 to 1%.
Synthetic emulsifying agents:
Anionic: Various alkali soaps, metallic soaps, sulphated alcohol and
sulphonates are used as anionic emulsifying agents. Soap emulsion
are used for external application.
18. Cationic: The quaternary ammonium compounds, such as
benzalkonium chloride, benzethonium chloride, cetrimide are used as
cationic emulsifying agents.
Non-ionic: The glyceryl esters, such as glyceryl monostearate sorbitan
fatty acid esters such as sorbitan monopalmitate are commonly used
non-ionic surface active agents.
Inorganic emulsifying agents: Several inorganic substances such as,
milk of magnesium (10-20%), magnesium oxide (5-10%) and
magnesium aluminium silicate (1%) are used to prepare coarse o/w
emulsion. Bentonite (5%) is used to prepare o/w or w/o emulsions.
Carbowaxes: These are mainly used in the preparation of ointments and
Cholesterol: In this category, cetyl alcohol, stearyl alcohol. cholesterol and
glyceryl monostearate are used to stabilize the emulsion.
Lecithins: Lecithins which forms w/o emulsion, is rarely used as an
PRESERVATION OF EMULSIONS
Emulsions which are prepared by using emulsifying agent, such as
carbohydrates, proteins, sterol and non-ionic surfactants may lead to
the growth of bacteria, fungi and moulds in the presence of water.
During storage of emulsions, the fats (obtained from vegetable and
animal sources) and emulsifying agents (such as wool fat, wool
alcohol) undergo oxidation by atmospheric oxygen. This can be
avoided by using antioxidant, such as, tocopherol, gallic acid, propyl
gallate and ascorbic acid.
Vanillin is a good flavouring agent for liquid paraffin emulsion.
Benzaldehyde is generally used as a flavouring agent for cod-liver
22. DRY GUM METHOD
Measure the required quantity of oil in a dry measure and
transfer it into a dry mortar.
Add the calculated quantity of gum acacia into it and triturate
rapidly so as to form a uniform mixture.
Add required quantity of water and triturate vigorously till a
clicking sound is produced and the product becomes white or
nearly white due to the total internal reflection of light. The
emulsion produced at this stage is known as primary emulsion.
Add more of water to produce required volume.
23. Example 7.1 Prepare and dispense 100 ml of arachis oil emulsion
using dry gum method.
Arachis oil 50.0 ml
Purified water add to 200.0 ml
Make an emulsion.
Method: Measure the required quantity of arachis oil in a dry measure
and transfer it into a dry mortar. gum acacia powder and triturate
rapidly to form a uniform mixture. Add required quantity of water and
triturate vigorously till a clicking sound is produced and product
becomes white. Add remaining water to produce the required volume.
Transfer the emulsion into a bottle, label and dispense. Prepare and
dispense the following emulsion.
24. WET GUM METHOD
Calculate the quantity of oil, water and gum required for preparing the
Powder the gum acacia in a mortar. Add water and triturate it with
gum so as to form a mucilage.
Add the required quantity of oil in small portions with rapid trituration
until a clicking sound is produced and the product becomes white or
nearly white. At this stage the emulsion is known as primary emulsion.
Add more of water in small portions to the primary emulsion with
trituration to produce the required volume. Stir thoroughly so as to
form a uniform emulsion.
Transfer the emulsion to a bottle, cork, label and dispense.
Castor oil 8 ml
Water add upto 30 ml
Make an emulsion.
Method: Powder the gum acacia tears in a mortar. Add water and
triturate to form a mucilage. Add the required quantity of castor oil
in small portions with rapid trituration until a clicking sound is
produced and the product became white or nearly white. Add more
of water in small portions to the primary emulsion with trituration to
produce the required volume. Transfer the emulsion to a bottle, label
26. BOTTLE METHOD
Bottle method is used for the preparation of emulsions of volatile
and other non-viscous oils. The proportion of oil:water:gum is 2:2.1
Measure the required quantity of the oil and transfer into a large
bottle. Add the required quantity of powdered gum acacia.
Shake the bottle vigorously, until the oil and gum are mixed
Add the calculated amount of water all at once.
Shake the mixture vigorously to form a primary emulsion.
Add more of water in small portions with constant agitation to
produce the required volume.
27. OTHER METHODS
Various blenders and homogenizers are used for preparing
emulsions. Hand homogenizer, Silverson mixer homogenizer and
colloidal mill are some of the homogenizers which are used for the
preparation of emulsions.
28. STABILITY OF EMULSIONS
An emulsion is said to be stable if it remains as such after it’s
preparation, i.e., the dispersed globules are uniformly distributed
through out the dispersion medium during its storage. The emulsion
should be chemically stable and there should not be any bacterial
growth during its shelf life.
Cracking means the separation of two layers of disperse and
continuous phase, due to the coalescence of disperse phase globules
which are difficult to redisperse by shaking.
Cracking may occurs due to the following reasons:
By addition of emulsifying agent of opposite type:
Soaps of monovalent metals produce o/w type emulsions whereas
soaps of divalent metals produce w/o type emulsions. But the
addition of monovalent soap to a divalent soap emulsion or a
divalent soap to a monovalent soap emulsion leads to cracking of
30. By decomposition or precipitation of emulsifying agents:
When an acid is added to an alkali soap emulsion (turpentine
liniment), it causes the decomposition of an emulsifying agent and
thus leads to cracking of an emulsion.
By addition of a common solvent:
When a solvent is added to an emulsion which is either miscible
with or dissolve the dispersed phase, the emulsifying agent and
continuous phase, there is formation of one phase or a clear solution.
This leads to cracking of an emulsion.
For example, addition of alcohol to turpentine liniment leads to the
formation of clear solution because turpentine oil, soft soap and
water are soluble in alcohol.
31. By microorganisms:
If emulsions are not stored properly, they may develop bacterial and
mould growth. This may lead to destruction of emulsifying agent
and cause cracking of emulsion.
Changes in temperature:
When emulsions are stored for a long time, an increase in
temperature may reduce the viscosity of the emulsion and encourage
creaming. When emulsions are stored at a very low temperature,
freezing of its water content into ice and subsequent melting of the
ice and shaking may reform the emulsion.
Creaming may be defined as the upward movement of dispersed
globules to form a thick layer at the surface of the emulsion.
Creaming is a temporary phase because it can be re-distributed by
mild shaking or stirring to get again a homogenous emulsion.
Radius of globules:
The rate of creaming is directly proportional to the radius of the
globules. Larger the size of the globules, the more will be creaming
and smaller the size of the globules, lesser will be creaming. The
small globules will rise less quickly than large globules. Hence,
creaming can be reduced by reducing the size of globules by passing
the emulsion through a homogeniser.
33. Viscosity of the dispersion medium:
The rate of creaming is inversely proportional to the viscosity of the
dispersion medium. The viscosity can be increased by adding
tragacanth and methyl cellulose. But too much viscosity is
undesirable because it may become difficult to re-disperse the
material which have settled at the bottom.
The emulsion should be stored in a cool place because the rise in
temperature reduces the viscosity which may lead to creaming. The
freezing should be avoided because it may lead to cracking.
34. Phase inversion:
Phase inversion means the change of one type of emulsion into the
other type i.e., oil in water emulsion changes into water in oil type
and vice versa.
It may be due to following reasons:
By the addition of an electrolyte
By changing the phase-volume ratio
By temperature change
By changing the emulsifying agent.
35. DIFFERENTIATION BETWEEN EMULSION AND
These are biphasic liquid
preparations containing two
immiscible liquids one of which
is dispersed as minute globules
into the other.
The globule size of the dispersed
liquid is in the range of 0.25 to 25
The emulsifying agent is required
to make a stable emulsion.
These are biphasic liquid dosage
form of medicament in which
finely divided solid particles are
dispersed in a liquid or semi-
The particle size of the
suspended solid is in the range of
0.5 to 5.0 micron.
The suspending agent is required
to make a stable suspension.
36. Emulsions are of two types i.e.,
oil-in-water type and water-in-oil
There are several tests to confirm
the type of emulsion.
During storage, freezing should
be avoided as it may lead to
cracking of emulsion.
Suspensions are of two types i.e.
flocculated and non-flocculated.
There is no test to identify the
type of suspension.
During storage, freezing should
be avoided as it may lead to
aggregation of the suspended