A positive reaction in a Sudan IV test is indicated by the appearance of a red or pink color in the layer containing the sample. This test is primarily used to detect the presence of lipids, which are fats and oils, in a substance.
When Sudan IV, a fat-soluble dye, is mixed with a sample that contains lipids, it binds to the lipid molecules. The dye has an affinity for lipid structures, and as it interacts with them, it demonstrates a distinct coloration. This is due to the formation of a complex between the dye and the lipids, which is visualized as a change in color.
In practical terms, you would mix the sample with Sudan IV and allow it to settle. If the sample has lipids, you’ll see a clear red-colored layer separated from the rest. No color change indicates a negative result, suggesting that the sample does not contain lipids.