Identification Test for Emulsion: An emulsion is a liquid preparation containing two immiscible liquids, one of which is dispersed as globules (dispersed phase = internal phase) in the other liquid (continuous phase = external phase).
- Droplets ranging in diameter (0.1-100 um).
- An emulsion is thermo-dynamically unstable and stabilized by emulsifying agent (emulgent or emulsifier).
- An emulsion is no more official in L.P.
- Emulsion protects the drug which is susceptible to hydrolysis and oxidation. It also provides prolonged action of the medication.
- In the form of an o/w emulsion, ephedrine has a more prolonged effect than when used in an oily solution when applied to the nasal mucosa.
Types of Emulsion
A primary emulsion containing one internal phase, for example,
- oil-in-water emulsion (o/w)
- water-in-oil emulsion (w/o).
The secondary emulsion also called multiple-emulsion contains two internal phases, for instance,
It can be used to delay the release or to increase the stability of the active compounds.
Identification Test for Emulsion
The addition of water to a w/o emulsion and oil to o/w emulsion would crack the emulsion and lead to the separation of the phases.
When current is passed to an emulsion connected to a voltage bulb, the bulbs glow if it is an o/w emulsion since water is a good conductor of electricity. When the bulb does not glow, it is w/o emulsion because oil is a non-conductor of electricity.
- o/w = current flow
- w/o = current do not flow
- o/w = current not flow (when purified water instead of potable water is taken)
The water-soluble dye will dissolve in the aqueous phase whereas the oil-soluble dye will dissolve in the oil phase. For example, Amaranth (0/w Emulsion), Scarlet/Sudan (w/o Emulsion).
Oils give fluorescence under UV light, while water does not. Therefore, O/W emulsion shows a spotty pattern while W/O emulsion fluorescence.
Filter paper test
o/w emulsion should spread out rapidly when dropped onto filter paper, in contrast, w/o will migrate slowly.
Cobalt chloride test
filter paper soaked in cobalt chloride (COCI) solution and allowed to dry, turn blue to pink on evaporation to o/w emulsion.
Pharmaceutical applications of emulsions
- To mask the bitter taste of the drugs.
- o/w emulsion is convenient means of oral administration of water-insoluble liquids.
- o/w emulsion facilitates the absorption of water-insoluble compounds comparing to their oily solution preparations (e.g. vitamins).
- Oil-soluble drugs can be given parenterally in form of an oil-in-water emulsion. (e.g. Taxol)
- An emulsion can be used for external applications in cosmetic and therapeutic uses.
Make sure you also check our other amazing Article on : Preparation of Lotions