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An emulsion is a biphasic liquid preparation
containing two immiscible liquid , one of
which is dispersed as a minute globule into
the others. The liquid which is converted
into minute globules is called dispersed
phase and liquid in which the globules are
dispersed is called the continuous phase
The emulsions are of two types :-
1. Oil in water type (o/w)
2. Water in oil type (w/o)
In oil-in-water type emulsion,the oil is in
dispersed phase where as water is in continuous
phase. The o/w type emulsions are preferred for
In water-in-oil type emulsion,the water is in the
dispersed phase whereas oil is in continuous
1. Dilution test
2. Dye test
3. Conductivity test
4. Fluorescence test
A. Classification of emulsions in accordance to the
type of emulsifying agents used in the
preparation of an emulsion :-
1. Emulsion containing natural gum e.g:- gum acacia,
2. Emulsion containing gum substitute e.g:- Cellulose
3. Emulsion containing saponins
4. Emulsion containing starch
5. Emulsion containing natural waxes e.g :- woolfat and
6. Emulsion containing synthetic wax e.g:-emulsifying
7. Emulsion containing other emulsifying agents such as
Emulsions for oral administration :- These are
usually o/w type of emulsions.
E.g:- cod liver oil
Emulsions for external use:- These may be either
o/w type or w/o type.
E.g:- oily calamine lotion
Emulsions for parenteral use:-These are used to
administer fat soluble vitamins such as A,D,E and oil soluble
sex hormones ,because there absorption in this form is very
Emulsions for rectal use:-These are used in
the form of enema for the evacuation of bowl.
starch mucilage is generally used in the
preparation of enema.
E.g:- Micralex citrato
The emulsifying agents reduce the interfacial
tensions between two phase i.e, oil phase and
aqueous phase and then make them miscible
with each other and form stable emulsion .
Emulsifying agents are also known as
emulgents or emulsifier
No. of the emulsifying agents are :
2. Polysorbate 20
3. Polysorbate 60
4. Polysorbate 80
SEMI-SYNTHETIC SYNTHETIC INORGANIC ALCOHOLICS
B. Preservation of emulsions:- Emulsions which
are prepared by using emulsifying agents such as
carbohydrates, proteins may lead to the growth of
bacteria, fungi in the presence of water.
In order to preserve emulsion properly:-
Benzoic acid (0.1-0.2%)
Methyl paraben and propyl paraben (0.1-0.2%)
c. Antioxidants :- During storage of emulsions the
fats and emulsifying agents under go oxidation by
atmospheric oxygen. This can be avoided by using
antioxidants such as
Gallic acid and
D. Flavours :- vanillin is a good flavouring agent for
liquid paraffin emulsions.
Benzaldehyde is generally used as a flavouring agent
for cod liver oil emulsions.
Stability of emulsions
An emulsion remain to be sable if it remains as such
after its preparation.
An emulsion is a heterogeneous system consisting of
at least one immiscible liquid dispersed in another in
the form of droplets. Emulsions are widely used in
such as the pharmaceutical, agricultural, cosmetic,
paint and food industries.
A second corollary of the positive free energy
change of emulsions is that most emulsions are
thermodynamically unstable. In order to prepare
emulsions with shelf life stability required for a
pharmaceutical product is about 1-3 years, it
depends upon the correct choice of emulsifiers be
made, polymeric stabilizers must be added.
The most common emulsifiers and emulsion
stabilizers are amphiphilic molecule with a pollar
group attached to an non-pollar group they may be
anionic cationic or non-ionic
Modernist thickeners and gelling ingredients can
make emulsions more stable. Besides giving
emulsions more texture, thickeners also help to
slow down the rate at which emulsions separate.
As the liquid is more viscous, the suspended
droplets can't move around so easily to
eventually combine in a specific area. This is
important for everything from a sauce, which
needs to stay emulsified for as long as it would
take a diner to eat it, to ice cream, which needs
to stay emulsified to prevent the growth or ice
Agar, gellan, gelatin, guar gum, sodium
alginate and xanthan gum can all be used as emulsion
stabilizers. You can learn more about each of these
ingredients in our Hydrocolloid Guide.
Suspensions are the biphasic liquid dosage form of
medicament in which the finely divided solids
particles ranging from 0.5 to 5.0 micron are
dispersed in a liquid or semisolid vehicles.
The particle size of disperse phase is very important
in the formulation of suspensions.
Qualities of a Good suspension
1. It should settle slowly and should be readily re-dispersed
on gentle shaking of the container
2. It should be chemically inert.
3. The suspension particle should not make a cake
4. The suspension should pour readily and evenly from its
Classification of suspensions
Suspensions are classified into four main parts
according to there pharmaceutical use:-
1. Oral Suspensions e.g :- Tetracycline HCL
2. Parenteral Suspensions e.g:- procaine pencilline G
3. Ophthalmic Suspensions e.g:- 2-amino butanol
4. Suspensions for external use e.g;- calamine lotion
Formulation of suspension :-
Flocculating agents:- In suspensions the solids
particles are well dispersed medium i.e vehicle. The
dispersion can be improved by adding a surfactant
or protective collides which acts as flocculating
agents . The flocculating agents acts by reducing
the surface tensions and thereby improving the
dispersions of solids and minimise flocculation
E.g:- sodium lauryl sulphate, tweens, spans etc.
Thickening agents:- These are hydrophilic
colloids which form colloidal dispersions with water
and increase the viscosity of the continuous phase,
so that the solid particle remains suspended in it
for a sufficient long time to measure a uniform
The thickening agents used to stabilise suspensions
are classified into three major groups
B. Inorganic agents
C. Synthetic compounds
Wetting agents:- These are the substances which
reduce the interfacial tensions between the solid
particles and liquid medium, thus producing a
suspension of required quality. This may be
achieved by adding a suitable wetting agent which
is absorbed at solid or liquid interface in such a
way that the affinity of the particles for the
surrounding medium is increased and the
interparticular forces are decreased
Preservative:- A suitable preservative is needed to
preserve suspensions against bacterial growth.
Preservative selected should be effective against a
wide range of microorganism.
Benzoic acid, sodium benzoate, methyl paraben
Organoleptic additives:- Colouring agents,
sweetening agents and flavouring agents are
generally incorporated in oral suspensions.
Some theoretic consideration are :-
1. Particle size control
4. Brownian movement
5. Electro kinetics or zeta potential
Evaluation of the stability of suspensions
Sedimentation method :- The measurement of
sedimentation volume is the most important
parameter in the evaluation of the stability of
suspensions. The suspension formulation (50ml)
was made separately into 100ml measuring cylinder
and sedimentation volume was read after At weakly
intervals for 12 weeks
Rheological methods :- It provides information
about settling behaviour. The arrangement of the
vehicle and the particle structural features.
Electro kinetic methods:- Measurement of Zeta
potential using micro electrophoresis apparatus and
zetaplus it shows the stability of dispersed system.
Micrometric method:- The stability of suspension
depends on the particle size of the dispersed phase
change in the particle size with reference to time
will provide useful information regarding the
stability of a suspensions