The two main ways to test for lipids in a sample substance is through the Sudan Red test and the Grease Spot test. Sudan Red is a dye that is lipid soluble. Therefore, when Sudan Red is added to a sample that contains lipids, the dye will colour the lipids red. The Grease Spot test can also be used identify the presence of lipids in a sample. Lipids make unglazed paper, such as the outside of a paper bag, translucent.
Use a cotton swab to apply a few drops of the sample to the paper bag.
Allow the sample to dry on the bag for several minutes.
Hold the paper bag up to a light after the sample has dried completely. If a grease spot remains, the sample contains lipids.
Measure 2ml of oil and 2ml of water.
Add the oil and water to the test tube.
Add 3 drops of Sudan Red.
Shake the test tube and observe. The Sudan Red will colour any lipids in the sample.
During the Grease Spot test, make sure to allow all spots to dry thoroughly. Otherwise, you may think that a wet spot is really a grease spot.
Be careful with the Sudan Red, because it can stain clothing.