Emulsifying agents: An emulsion is a biphasic liquid dosage form in which one of the liquids is broken down into minute globules each surrounded by thin layers of emulgent. The liquid broken down is called the dispersed phase and the liquid in which the globules are dispersed is called the continuous phase. They are two types i.e. o/w and w/o type.
Table of Contents
Classification of emulsifying agents:
- Natural emulgents from vegetable sources:
- Acacia
- Tragacanth
- Agar
- Chondrus
- Pectin
- Starch
- Natural emulgents from animal sources:
- Gelatin
- Egg yolk
- Wool fat
- Semi-synthetic polysaccharides:
- Methylcellulose
- Sodium carboxymethyl cellulose
- Synthetic emulgnets:
- Anionic
- Cationic
- Non-Ionic
- Inorganic emulsifying agent:
- Milk of magnesia
- Magnesium oxide
- Magnesium trisilicate
- Magnesium aluminum silicate (veegum)
- Aluminum silicate (hectorite)
- Magnesium silicate (Hectorite)
- Saponins
- Alcohols
- Cholesterol
- Carbowaxes
- Lecithin
1. Natural emulgents from vegetable sources:
They include gums and mucilagenous substances.
Acacia: Best emulgents for the preparation of emulsion for internal use.
The ratio of acacia :
For fixed oil is 1:4
For volatile oil 1:2
For mineral oil 1:3
Tragacanth: Rarely used as an emulgent because it doesn’t reduce interfacial tension. It usually produces coarse and thick emulsions and so viscosity increases to such an extent that pouring of emulsion becomes problem. A very stable emulsion is formed if acacia and tragacanth are combined.
Agar: Not a good emulgent can be used in combination with acacia.
Pectin: Acts as emulsion stabilizer.
Starch: Rarely used as emulgent.
2. Natural Emulgents from animal sources.
a) Gelatin: Gelatin emulsions are prone to bacterial growth, hence a preservative is incorporated.
b) Egg yolk: Rarely used as emulsion gets spoiled during transportation.
c) Wool Fat: Mainly used in emulsion meant for external application.
3. Semisynthetic polysaccharides:
a) Methyl Cellulose: This is a synthetic derivative of cellulose and widely used in industries as suspending, thickening and emulgent.
b) Sodium Carboxymethyl Cellulose: Not a good emulgent but can be used as emulsion stabiliser.
4. Synthetic Emulgent:
This group includes surfactants. They possess ionic charge.
eg: a) anionic b) Cationic c) non-ionic.
a) Anionic: They bear negative charge on them
eg Sodium lauryl sulphate, diocetyl sodium sulphoscuccinate.
b) Cationic: They bear positive charge on them used as germicidal agents. eg: Benzalkonium chloride, cetrimide.
c) Non-ionic: Most commonly used surfactants are glyceryl esters such as glycerylmonostearate polyoxyethylene glycol esters.
5. Inorganic Emulgents:
Several inorganic substances such as milk of magnesia, magnesium trisilicate, magnesium aluminium silicate are used in the preparation of emulsion.
6. Saponins:
Rarely used as emulgents. eg: quillaia tincture.
7. Alcohols:
a) Cholesterol: Cetyl alcohol, stearyl alcohol, glyceryl monostearate may be included in this group.
b) Carbowaxes: Acts as non-ionic emulgent.
c) Lecithin: Usually forms w/o emulsion it is rarely as it darkens in colour and gets oxidized easily.
Also read: Define emulsion, describe the preparation of emulsion