Emulsions.ppt

JSS College of Pharmacy, Mysuru
Emulsions
1

Syllabus
• Emulsions: Definition, classification,
emulsifying agents test for the identification
of type of Emulsion, Methods of preparation
& stability problems of emulsions and
methods to overcome.
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Definition
• An emulsion is a biphasic liquid preparation
containing two immiscible liquids, one of
which is dispersed as minute globules into the
other.
• The liquid Phase that is converted into minute
globules is called the Dispersed Phase and the
liquid in which the globules are dispersed is
called the Continuous Phase.
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Advantages of Emulsions
1. Mask unpleasant taste: by introducing the bitter substances in the internal
phase and masking it by the external phase.
Ex. Laxative , phenolphthalein, Vitamin A.
2. Economical: Expensive solvents (Vehicles) are required to dissolve lipids. In
emulsions, lipids can be dispersed in water.
3. Improved Bioavailability: Absorption of drugs faster and better in emulsion
dosage forms.
Ex: Corn-oil /water emulsion of Griseofulvin – otherwise erratic absorption
from tablets.
4. Emulsions provide protection against drugs which are prone to oxidation or
hydrolysis.
5. Various external preparations such as creams, lotions and foams are
formulated as emulsion dosage forms.
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Disadvantages of Emulsions
• Short shelf life
• Unstable and liquid phase separates slowly
• Being Liquid dosage forms, these are packed
in glass or plastic containers. Hence, care
should be taken in handling and storage.
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Classification of Emulsions
• Oil in water emulsion [O/W]
• Water in Oil Emulsion [W/O]
Oil in water emulsion [O/W] :
 in oil in type of emulsion, the oil is in the dispersed
phase where as water is in the continuous phase.
 The O/W type of emulsions are preferred for internal
use.
 In this emulsions, gum acacia, tragacanth, methyl
cellulose, saponins, synthetic substances and soaps
formed from monovalent basees like Na+, K+ and
NH4+ are used as an emulsifying agent.
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• Water in Oil Emulsion [W/O]
 In W/O type of emulsion, the water is in the
dispersed phase whereas oil is in the
continuous phase. The wool fat, resins,
beeswax and soaps form divalent bases like
Ca++, Mg++ and Zn++ are used as on
emulsifying agent.
 The W/O type of emulsions are mainly used
externally as lotions or creams.
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DIFFERENCE BETWEEN O/W AND W/O EMULSIONS
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Water in oil emulsion (w/o)
Oil in water emulsion (o/w)
Oil is the dispersion medium and water is the
dispersed phase
Water is the dispersion medium and oil is the
dispersed phase
They are greasy and not water washable
They are non greasy and easily removable
from the skin surface
They are used externally to prevent evaporation
of moisture from the surface of skin e.g. Cold
cream
They are used externally to provide cooling
effect e.g. vanishing cream
Oil soluble drugs are more quickly released
from w/o emulsions
Water soluble drugs are more quickly
released from o/w emulsions
They are preferred for formulations meant
for external use like creams.
They are preferred for formulations meant for
internal use as bitter taste of oils can be
masked.
W/O emulsions go not give a positive
conductivity test as oil is the external phase
which is a poor conductor of electricity.
O/W emulsions give a positive conductivity
test as water is the external phase which is a
good conductor of electricity.

Tests for identification of type of emulsion
• The following tests are done to distinguish between o/w
and w/o emulsions.
1. 1. Dilution test:
Dilution of an emulsion either with oil or water can
reveal its type
Fact: More of the continuous phase can be added to the
emulsion without causing instability.
Example: if a 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.
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• 2. 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
colourless, the emulsion is o/w type The
reverse condition occurs in w/o type emulsion
ie., the disperse globules appear colourless in
the red "ground'
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• 3. 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 phase.
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• 4. Fluorescence test 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 field
fluorescence indicates that oil is present in
continuous phase (w/o emulsion) and droplets
fluorescence indicates that oil is present in
dispense phase (o/w type emulsion)
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5. Creaming test: O/W emulsion cream upwards and
W/O emulsion cream downwards
6. Cobalt Chloride Test: Filter paper soaked in cobalt
chloride solution and allowed to dry turns blue to pink
on exposure to o/w emulsions
This may not work for unstable emulsions
7. Filter paper Test: This test is based on the fact that an
o/w emulsion will spread out rapidly when dropped
onto filter paper. In contrast a w/o emulsion will
migrate only slowly.
This method should not be used for highly viscous
emulsions (Creams)
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Emulsifying agents
• The emulsifying agents reduce the interfacial tension between two
phases; Oily phase and aqueous and make one disperse in the other
and at certain levels; act as a solubiliser.
• Emulsifying agents stabilize emulsions by preventing/ reducing
coalescence (the process of coming or growing together to form
one thing or system) of dispersed globules,. They posses certain
type of affinity to polar and non polar liquids. Consequently the
emulsion is stabilized.
• There are number of emulsifying agents which are available to form
stable emulsions. But It is difficult to develop proper emulsifying
agent for the development of stable emulsions.
• Sometimes two or more emulsifying agents are required.
• Emulsifying agent also called as emulsifier or emulgent.
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Properties of an ideal emulsifying
agent
An Ideal Emulsifying agent should posses following
properties:
1) It should be capable of reducing interfacial tension between
the two Immiscible liquids
2) It should be compatible with other ingredients of the
preparation.
3) It should be non-toxic.
4) It should be capable to produce and maintain the required
consistency of the emulsion.
5) It should be chemically stable.
6) It should be capable of keeping the globules of dispersion
liquid distributed Indefinitely throughout the dispersion
medium.
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Classification of Emulsifying agents
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Natural Semi synthetic
Polysaccharides
Synthetic Inorganic Alcohols
Vegetable
source:
Gum Acacia
Tragacanth
Agar
Pectin
Starch
Irish Moss
(Chondrou)
Methyl cellulose
Sodium carboxy-
Methyl cellulose
Anionic
Cationic
Non-ionic
Amphoteric
-Milk of
Magnesia
-Magnesium
Oxide
-Magnesium
Trisilicate
Magnesium
Aluminium
silicate
Bentonite
Carbowaxes
Cholesterol
Lecithin
Cetyl Alcohol
Stearyl Alcohol
Cetostearyl alcohol.
Animal Source:
Wool Fat
Egg Yolk
Gelatin.
Bees Wax
Synthetic Polymers
Carbomer
(acrylic acid
polymer)

• Anionic, e.g., alkali soaps (sodium or potassium oleate);
amine soaps (triethanolamine stearate); detergents
(sodium lauryl sulfate, sodium dioctyl sulfosuccinate,
sodium docusa
• Cationic surfactants are essentially quaternary
ammonia compounds with positively charged surface-
active moieties (e.g. benzalkonium, benzethonium,
methylbenzethonium, cetylpyridinium, alkyl-dimethyl
dichlorobenzene ammonium)
• An amphoteric emulsifier is a compound that contains
anionic as well as a cationic hydrophilic group.
• Non-Ionic Emulsifer is a non-anionic emulsifier and is
appreciated for accurate composition and reliable
performance. The additive is formulated using the finest
quality raw material.
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Preparation of Emulsions
On small scale preparation of emulsions the
following methods are used:
1. Dry Gum Method
2. Wet Gum Method
3. Bottle Method
4. Other methods.
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Dry Gum Method
• Widely employed method for preparing emulsions
using dry gum emulgents, like acacia
• The proportion of gum to be used depends upon the
nature of oil – Primary emulsion formula
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Nature of Oil Oil Water Gum
Fixed Oils
(Castor oil, Cod liver oil, Almond oil)
4 2 1
Mineral Oils
(Liquid Paraffin)
3 2 1
Volatile Oils
(Turpentine oil, Peppermint oil, Cinnamon oil)
2 2 1

Dry Gum Method Cont..
• A dry mortar and pestle and a dry measuring
cylinder is used
• Measured quantity of oil is thoroughly triturated
with acacia in the mortar
• Twice as much aqueous vehicle (water) as the
gum is added all at once to the contents in mortar
and rapidly triturated till a thick cream is formed
• This product known as “Primary Emulsion” and is
characterized by a clicking sound on brisk
triturating
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Dry Gum Method Cont..
• Remaining quantity of water is then added
gradually to the primary emulsion with
trifurcation
• Emulsion is then transferred to measure and the
volume is adjusted, rinsing out the mortar with
additional water
• The final product is stirred to get a uniform
product
• The product is clarified by straining through
muslin cloth or by decanting the supernatant after
allowing the impurities to settle
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Emulsion – preparation – Dry gum
method
Prepare and Dispense 100ml of arachis oil emulsion using
dry gum method:
Arachis oil -------------- 50ml
Purified water to ------200ml
Arachis oil is a fixed oil. So for primary emulsion ratio will be
Oil : Water: Gum is 4:2:1
Arachis oil ---------------50ml
Water --------------------25ml
Acacia powder ----------12.5 g
• Make primary emulsion by dry gum method, add remaining
water to make up the volume.
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Wet Gum Method
• In this method, the proportion of Oil : Water : Gum for
preparing the primary emulsion is same as discussed before.
Method:
1)Calculate oil, water and gum required for preparing the
primary emulsion.
2) Powder Gum acacia in a mortar. Add water and triturate it
with gum so as to form a mucilage.
3) Add 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.
4) Add more water in small portions to the primary emulsion
with trituration to produce required volume. Stir thoroughly
so as to form uniform emulsion.
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Bottle Method
• Bottle method is Used for preparation of emulsion of
volatile and other non-viscous oils.
• The proportion of oil : Water : Gum = 2 : 2 : 1
• Measure the required quantity of the oil and transfer into a
large bottle. Add the required quantity of powder of
powdered gum acacia.
• Shake the bottle vigorously until the oil and gum are mixed
thoroughly.
• 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 continuous
agitation to produce the required volume.
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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
extemporaneous emulsions. The homogenizers are
based on the principle that the large globules in course
emulsion are broken into smaller globules by passing
them under pressure through a narrow orifice.
• A course emulsion is prepared in a mortar which is then
transferred into hand homogenizer. The emulsion is
passed through a homogenizer many a times till an
emulsion of desired satisfaction is produced.
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Stability problems of emulsions.
• An emulsion is said to be stable if it remains as such after
its preparation i.e. the dispersed globules are uniformly
distributed in the dispersion medium during its storage.
• The emulsion should be chemically stable and there should
not be any bacterial growth during the shelf life.
Following three changes usually occur during the storage of
emulsions.
1)Cracking
2)Creaming
3)Phase Inversion
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JSS College of Pharmacy, Mysuru 27
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1.Cracking
• Separation of two layers of dispersed and continuous phase, due to
the coalescence of the dispersed phase globules which are difficult
to readily re-disperse by shaking. Cracking may occur due to
following reasons.
a)By addition of emulsifying agent of opposite type:
• Adding Divalent soap to an emulsion stabilized by monovalent soap
and vice versa can lead to cracking of emulsion.
b)By decomposition or precipitation of emulsifying agents:
• Acid added to alkali
• Soap emulsions, causes decomposition of emulsifying agent.
• In the same way adding sodium chloride to emulsion stabilized by
sodium or potassium soap, lead to precipitation of the emulsifying
agent, the soap . Therefore the cream cracks.
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1.Cracking Cont..
c) By addition of common solvent: When a solvent is added to an emulsion
which is either miscible with or dissolve the dispersed phase, emulsifying
agent and the dispersion medium, there is a formation of one phase or a
clear solution. This leads to cracking.
• For Ex. Additional of alcohol to turpentine liniment leads to the formation
of a clear solution because turpentine oil, soft soap and water are soluble in
alcohol.
d) By Micro-organisms: Micro contamination of an emulsion may lead to
destruction of the emulsifying agent and cause cracking of emulsions.
• Therefore the formula should be well designed and suitably preserved.
e) Change of Temperature: Storage at high temperature may reduce viscosity
of the emulsion and encourage creaming. At very low temperature,
continuous phase water will form ice
• The emulsion might reform after bringing back to room temperature and
shaking.
f) By creaming: An emulsion that tend to cream is more liable to crack than an
homogenous emulsion. Therefore formula should be designed to avoid
creaming
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2. Creaming
• Creaming may be defined as 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-dispersed by shaking or stirring to get an
homogenous solution. Since creaming can lead
to cracking, creaming should be avoided.
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2. Creaming Cont..
• Creaming: According to Stoke’s law
Stoke’s equation
2r2 (ρs- ρ o ) g d2 (ρ s- ρ o ) g
V= ---------------- or V = ---------------
9o 18o
Where,
V = Rate of Creaming
d = Diameter of particle
r = radius of particle
ρ s= density of disperse phase
ρ o= density of disperse media
g = acceleration due to gravity
ηo = viscosity of disperse medium in poise
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2. Creaming Cont..
• Radius of Globule: Rate of creaming is directly proportional
to the radius of the globule.
• Difference in density of dispersed phase and dispersion
medium: Grater the difference more will be the creaming.
• Viscosity of the dispersion medium: Higher the viscosity
lower will be the creaming. However the product should
have consumer and product friendly rheological properties.
Must be able to shake and mix the product if required, and
for consumers it should be pourable from the container.
• Extreme storage conditions should be avoided. Higher
temperature may lead to viscosity drop and lower
temperature may freeze the water phase and can cause
creaming when brought to room temperature.
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3. Phase Inversion
• Phase Inversion means change of one type of emulsion to
the other type. i.e. O/W changing into W/O and vice versa.
• It may be due to following reasons.
1)Addition of electrolyte
2)Changing the phase volume ratio
3)Changing temperature
4) Changing Emulsifier
• Phase inversion can be minimized by keeping concentration
of the dispersed phase between 30-60%, Storing the
emulsion in cool place and by using proper emulsifying
agent at optimum concentration.
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Differentiation between Emulsion and Suspension
Sl
No
Emulsion Suspension
1 These are biphasic liquid preparations
containing two immiscible liquids one of
which is dispersed as minute globules into
another
These are biphasic liquid dosage forms of
medicament in which finely divided solid
particles are dispersed in a liquid or
semisolid vehicle.
2 The globule size of the dispersed liquid is
in the range of 0.25 to 25 microns
The particle size of the suspended solid is
in the range of 0.5 to 5.0 micron
3 Emulsifying agent is required to make a
stable emulsion
Suspending agent is required to make a
stable suspension
4 Emulsion are of two types. O/W & W/O Suspensions are of two types flocculated
and non-flocculated
5 There are several tests to confirm the type
of emulsion
There are no tests to identify the type of
suspension
6 During storage freezing should be avoided
as it may lead to cracking of emulsion
During storage, freezing should be avoided
as it may lead to aggregation of the
suspended particles
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Thank You
2/7/2023 35

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