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Emulsion | Definition, classification, advantage, disadvantage, preparation, testing | imdip

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The emulsion is a widely used biphasic liquid dosage form. There is a lot of application of emulsion in the pharmaceutical, cosmetics, paint industries.

Emulsion | Definition, classification, advantage, disadvantage, Formulation, testing

Emulsion | Definition, classification, advantage, disadvantage, preparation, testing

Definition of Emulsion:

An emulsion is a biphasic liquid dosage form. An emulsion is a mixture of two or more liquids that are normally immiscible to each other but using emulsifying agents one liquid is dispersed into other liquid as droplets.

So, there are two phases in an emulsion. One is the dispersed phase and another is the continuous phase. The concept is a dispersed phase (liquid), which is dispersed or spread in the other phase(continuous phase). You can see the picture given below to easily understand.

Examples of emulsions: Milk (fat in water), Butter (water in oil), Liquid paraffin (paraffin in water), etc.

Learn: Suspension | Definition, classification, advantage, disadvantage, preparation methods 

Oil in water emulsion, water in oil emulsion

Uses of Emulsion:

  • Pharmaceutical Application: Due to the high bioavailability and absorption rate, it used in the pharmaceutical industry. Mostly it used for topical preparations like creams, lotions, etc.
  • Cosmetic industry: There is a huge application of emulsion in the cosmetic industry. Example: creams, lotions, hair conditioners, etc.
  • Food industry: Food products like milk, peanut butter, ice cream, etc. are some examples of emulsion. So you can easily understand the application of emulsion in this industry.
  • Paint industry: Examples like emulsion paints and inks.

Advantages of Emulsion:

1.Cover up the unpleasant taste.
2.Increase the bioavailability of the dose.
3.Sustained release medication.
4.Very cost-effective

Disadvantages of Emulsion:

1.Problem of creaming and sedimentation
2.Phase inversion
3.problem of handling

Classification of Emulsion:

Basically, there are three types of emulsions-

Types of emulsion

1. Simple Emulsion: 
Oil in Water (O/W) Emulsion
Water in Oil (W/O)Emulsion

2. Multiple Emulsions:
Water-in-Oil-in-Water (W/O/W) Emulsion
Oil-in-Water-in-Oil (O/W/O) Emulsion

3. Micro Emulsions: Size of droplets 10- 200nm
Oil-in-Water Micro Emulsions
Water-in-Oil Micro Emulsions

Difference between Oil in water emulsion(O/W) and Water in oil emulsion(W/O):

 Oil in water emulsion(O/W) Water in oil emulsion(W/O)
For O/W emulsion-water is the continuous phase and oil is the dispersed phase For O/W emulsion-water is the continuous phase and oil is the dispersed phase
Less viscous and easily washable from the skin by water More Viscous than O/W and not easily washable from the skin by water
Example- Vanishing cream Example- Cold cream

Multiple Emulsions: In the case of multiple emulsions, the dispersed phase contains smaller droplets of the continuous phase.

Definition of Emulsifying Agent (Emulsifier):

The emulsifying agent is a surface-active substance to make an emulsion, which is both fat and water-soluble. It helps the dispersed phase to uniformly dispersed in the continuous phase.

Examples of Emulsifying agent(Emulsifier):

Natural Emulsifying Agents: Acacia, Tragacanth, etc.

Synthetic Emulsifying Agents: Polysorbate 20, Polysorbate 80, Sodium lauryl sulfate(SLS), Sorbitan laurate, Sorbitan stearate, etc.

Classification of Emulsifying Agent:

1. Natural emulsifying agents:
  • Vegetable sources- Agar, Tragacanth, Gum acacia, etc.
  • Animal sources- Wool fat, Gelatin, etc.

2. Semi-synthetic emulsifying agents: Methylcellulose, Sodium CMC, etc.

3. Synthetic emulsifying agents:
  • Anionic emulsifying agents: Sodium lauryl sulfate(SLS)
  • Cationic emulsifying agents: Benzalkonium Chloride
  • Non-ionic emulsifying agents: Glyceryl ester
  • Inorganic emulsifying agents: Milk of magnesia

Classification of emulsifying agents

Formulation or Preparation of Emulsion:

Method of preparation of emulsion:

1. Trituration Method:

(i) Dry Gum Method
(ii) Wet Gum Method

2. Bottle or Forbes Bottle Method

3. Auxiliary Method

4. Nascent Method or In Situ Soup Method

5. Beaker Method

Emulsion testing parameters and methods:

  • Dilution test: This test is important to know the solubility of the continuous phase of the emulsion. For example- In O/W emulsion, a dilution test is done to know it's diluted with water or not.
  • Conductivity Test: This test is important to know, which is a good conductor of electricity to find out the continuous phase. For example- In O/W emulsion, water is a continuous phase. Because water is a good conductor of electricity than oil.
  • Dye-Solubility Test: This test is done by mixing the emulsion with water or an oil-soluble dye, and checked under a microscope to know which is in a continuous phase or dispersed phase.
  • Fluorescence test: Oils have the property of fluorescence under UV light, while water doesn’t. Therefore, O/W emulsion shows a spotty pattern while W/O emulsion fluoresces.

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