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How to identify the type of emulsion?

Identification of Emulsion type.


Basically, emulsions are of two types : o/w and w/o.


Following tests are conducted in order to identify the type of emulsion.

1. Cobalt chloride test:
Filter paper soaked in cobalt chloride solution and dried, changes colour from blue to pink when exposed to the o/w (oil in water) emulsion.

2. Dilution test:
This test is based on the miscibility of continuous phase in the oil or water. For example, if water is added with stirring in o/w emulsion, it will easily disperse in added phase (water) but w/o emulsion will not get dispersed.
This method causes phase inversion of emulsions upon dilution.

3. Conductivity test:
An emulsion with water as a continuous phase (o/w emulsion) passes the electric current, whereas the w/o emulsion is not able to do so.

4. Direction of creaming:
When densities of the water and oil phases are known, direction of creaming test identifies emulsion type. 
Creaming in:
o/w emulsion: upward creaming (density of oil is less than water)
w/o emulsion: downward creaming

5. Dye test:
When amaranth, a water soluble dye is mixed with oil-in-water(o/w) emulsion, upon microscopic study continuous phase (water) is coloured.
When Sudan red III is mixed with an emulsion and microscopically it shows colored continuous phase, the emulsion must be water-in-oil type (w/o).
The reason behind it is the Sudan red III is an oil soluble dye.

6. Filter paper test:
When this test is applied to test the type of emulsion, a drop of Emulsion is added on filter paper.
If emulsion is o/w type, the water spreads rapidly on the paper.
If emulsion is w/o, the continuous phase oil spreads relatively slower on the paper.
This test is not carried out for the viscous creams.

7. Fluorescence test:
In this method, a drop of emulsion is exposed to the ultraviolet light and observed under the microscope.
Many oils show fluorescence upon exposure to ultraviolet light.
If the emulsion is o/w, only suspended globules will show fluorescence and in w/o emulsion, continuous fluorescence will be seen.



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