2.1.3—Emulsion test for lipids

The emulsion test is a qualitative test for lipids. Lipids do not dissolve in water, but they dissolve in ethanol; adding the ethanol-containing sample to water produces a milky emulsion when lipid is present.

1. Add ethanol to the sample and shake to dissolve any lipid present.
2. Add the ethanol–sample mixture to water and mix.
3. Observe the final mixture: a cloudy or milky emulsion indicates lipid; a clear mixture is a negative result.

Ethanol acts as the solvent that carries dissolved lipid into the water. Lipid does not remain dissolved when water is added, so it forms many small droplets that scatter light and make the mixture appear milky.

The emulsion test indicates that lipid is present; it is not an exact concentration assay. Keep sample volume, ethanol volume, water volume and mixing/observation conditions consistent when comparing samples, and do not add water before the sample has been mixed with ethanol.