Why do we use Sudan III to identify lipids?
Sudan III, 1-(4-(phenyldiazenyl)phenyl) azonaphthalen-2-ol, is a member of Sudan dyes that are used for lipid testing. Basically this dye is used to color non polar organic substances such as oils, fats, waxes and other long chain hydrocarbon molecules.
In biochemistry laboratory, Sudan III is used for lipid determination. Sudan III solution has a red-brown color. For lipid testing, the Sudan III solution is added in the aqueous solution of lipids. It should create two layers; the aqueous layer at the bottom and the Sudan III solution on top. The test will be positive when the red (sometimes red-orange) solution of the Sudan Red will decolorize the aqueous solution. It only means that the lipid particles in the aqueous layer will dissolve the Sudan III dye. It will show negative test when the two layers will not change even when the mixtures are shaken.