Identification of emulsion is done by following methods

;

1. Dye Solubility test:

• Water-soluble dye -Amaranth and Methylene blue-form uniform tint in O/W emulsion.
• Sudan III & Scarlet Red (oil-soluble dye)-form uniform tint in W/O emulsion.

2. Dilution test

• When a dispersion medium (i.E. External/continuous phase) is added to an emulsion, NO phase separation occurs.
  • When water is added to O/W  emulsion-  no phase separation; if the oil is added to O/W  emulsion-  phase separation takes place.
  • When the oil is added to W/O  emulsion-  no phase separation occurs; if the water is added to O/W  emulsion-  phase separation takes place.

3. Conductivity test

This test is based on the ability of water to conduct electricity. If water is the continuous phase (i.e. O/W), then the emulsion conduct electricity.  if oil is the continuous phase (i.e W/O emulsion), the emulsion fails to conduct electricity.

4. Creaming test

• (direction of creaming upward or downward)
• W/O emulsion: normally cream downwards as well is usually less dense than water
• O/W emulsion: normally cream upwards

5. Other tests: 

• Cobalt chloride test filter paper test (blue to pink, indicating that the emulsion is o/w type.) &
• Fluorescence test (fluorescence under microscope, then it is w/o type and if it shows only spotty fluorescence, then it is o/w type)

Also, Read…

Introduction to Emulsion

Type of Pharmaceutical Emulsion

Formulation of Emulsion

Physical Instability of Emulsion