Evaluation of Emulsions – Pharmaceutics – I B. Pharma 1st Semester

Evaluation of Emulsions

Learning Objectives

At the end of this
lecture, student will be able to

• Identify instabilities in emulsions and suggest suitable
remedial measures

• Explain the various methods used for evaluation of

Instabilities in Emulsions

Instabilities seen in emulsion can be grouped as:

1. Cracking

2. Creaming

3. Phase inversion

1. Creaming

• Separation of an emulsion into 2 regions

• One region is richer in the disperse phase than the other

• Not a serious instability

• Uniform dispersion on shaking

• But creaming can lead to cracking

Types of Creaming

1. Upward creaming

2. Downward creaming

1. Upward creaming

– If the disperse phase is less dense than the continuous

– The velocity of sedimentation becomes negative

– Seen in O/W emulsions

2. Downward creaming

– If the internal or disperse (aqueous) phase is heavier
than the external or continuous (oil) phase

– The globules settle

– Seen in W/O emulsions

Factors governing

Stoke’s law is used to express the velocity of sedimentation

where,           V =
velocity in cm/sec {rate of creaming}

r = radius of the globules

d = diameter of the globules in cm

Ps = density of dispersed phase

Po = density of dispersion medium

g = gravitational constant

n= viscosity of the dispersion medium

Causes of Creaming

• Increase in the diameter of the globules.

• Decrease in the viscosity of the external or continuous

• Increase in density differences between the disperse phase
and dispersion medium.

• Variations in storage temperature

Can the emulsion be

• The emulsion will reform on shaking.

• Reversible process

• But creaming can lead to cracking

Prevention of

• Decreasing the diameter of the oil globules —

• Increasing the viscosity of the external / continuous
phase — addition of a thickening agent.

• Reduction in density differences between the 2 phases—
using phases which have similar density

•Storage in a cool place

2. Cracking

• Globules of the disperse phase coalesce and separate into
a different layer

• Redispersion cannot be achieved by shaking

• The preparation is no longer an emulsion.

Causes of Cracking

1. Addition of emulsifying agents of the opposite type:

Soaps of monovalent
metals – O/W emulsions and soaps of divalent metals – W/O emulsions.

2. Gums, proteins – gelatin & casein are insoluble in
alcohol – if alcohol is added, the emulgent is precipitated – cracking occurs.

3. Decomposition of the emulsifying agent due to microbial

4. Addition of common solvent

5. Oil is Rancid

6. Change of storage temperature

Can the emulsion be

• The emulsion will not reform on shaking

• It is an irreversible process.

Prevention of

• Choose the correct emulsifying agent

• Avoid use of common solvent

• Use of preservatives

• Maintain constant temperature conditions for storage

• Use fresh oil for preparation


3. Phase

• Oil-in-water emulsion changes to a water-in-oil emulsion


• Water-in-oil emulsion changes to oil-in-water emulsion.

Causes of Phase

• Addition of the wrong emulsifying agent

E.g. If calcium chloride is added to an O/W emulsion
stabilized by sodium soap, phase reversal may occur resulting in W/O emulsion.

• Increase in concentration of disperse phase beyond 60%

Can the emulsion be

• The emulsion will not reform on shaking

• It is an irreversible process

Prevention of Phase

• Using the proper emulsifying agent in adequate

• Maintaining the concentration of dispersed phase between
30 to 60 %

• Storing the emulsion in a cool place.

of Emulsions

1. Macroscopic
Calculating the volume of the creamed or separated part of the
emulsion to the total volume.

2. Globule size
By microscopic examination / electronic particle counting devices
such as coulter counter / by Laser diffraction.

3. Viscosity changes:
Brookefield’s Viscometer.

of Emulsions

1) Preservation from
Use suitable preservatives

2) Preservation from
Use anti- oxidants

for Emulsions



1) Instabilities in

– Creaming:
Separation of an emulsion into 2 regions and one region is richer in the
disperse phase than the other

– Cracking:
Separation on an emulsion into two separate layers

– Phase Inversion:
Conversion of O/W emulsion into W/O emulsion and vice versa

2) Preservation of
Using preservatives

3) Labeling of
Shake Well Before Use

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