Emulsions

Question 1

What is an Emulsion

Answer 1

An emulsion is a liquid preparation containing a mixture of oil and water that is rendered homogeneous by the addition of an emulsifying agent.

Question 2

O/W (Oil in Water)

Answer 2

The emulsifying agent ensures that the oil phase is finely dispersed throughout the water as minute globules (droplets). This type of emulsion is termed an ‘o/w’ emulsion.

Question 3

O/W

Answer 3

The oily phase (disperse/internal phase) is dispersed through the aqueous phase (continuous/external phase).

Question 4

W/O

Answer 4

The water phase (disperse/internal phase) is dispersed through the oily phase (continuous/external phase).

Question 5

Stability of Emulsions

Answer 5

Emulsions can break down in the following ways: ■ cracking ■ creaming ■ phase inversion.

Question 6

Cracking

Answer 6

This is the term applied when the disperse phase coalesces and forms a separate layer. Redispersion cannot be achieved by shaking and the preparation is no longer an emulsion. Cracking can occur if the oil turns rancid during storage. The acid formed denatures the emulsifying agent, causing the two phases to separate.

Question 7

Creaming

Answer 7

In creaming, the oil separates out, forming a layer on top of the emulsion, but it usually remains in globules so that it can be redispersed on shaking (e.g. the cream on the top of a pint of milk). This is undesirable as the product appearance is poor and if the product is not adequately shaken there is a risk of the patient obtaining an incorrect dose. Creaming is less likely to occur if the viscosity of the continuous phase is increased.

Question 8

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Answer 8

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Question 9

Summary of problems caused encountered by emulsions; Creaming

Answer 9

Separation of the emulsion into two regions, one containing more of the disperse phase. Possible reasons for problem ■■ lack of stability of the system ■■ product not homogeneous. Can the emulsion be saved? The emulsion will reform on shaking.

Question 10

Summary of problems caused encountered by emulsions; Cracking

Answer 10

Cracking The globules of the disperse phase coalesce and there is separation of the disperse phase into a separate layer. Possible reasons for problem: ■■ incompatible emulsifying agent ■■ decomposition of the emulsifying agent ■■ change of storage temperature. Can the emulsion be saved? The emulsion will not reform on shaking.

Question 11

ags

Answer 11

Phase inversion From oil-in-water to water-in-oil or from water-in-oil to oil-in-water. Possible reason for problem ■■ amount of disperse phase greater than 74%. Can the emulsion be saved? The emulsion will not reform on shaking.