Identification Test for Emulsion

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,

  • o/w/o
  • w/o/w.

It can be used to delay the release or to increase the stability of the active compounds.

Identification Test for Emulsion

Dilution test

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.

Dilution test
Fig: Dilution test

Conductivity test

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)
Conductivity test
Fig: Conductivity test

Dye test

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).

Dye test
Fig: Dye test

Fluorescent test

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.
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