Sudan IV is a lysochrome (fat-soluble dye) diazo dye used for the staining of lipids, triglycerides and lipoproteins on frozen paraffin sections. It has the appearance of reddish brown crystals with melting point 199 °C and maximum absorption at 520(357) nm.
Sudan IV is lipophilic diazo dye, very similar to Sudan III. It is primarily used in Sudan IV staining method or in Churukian's variety of Lillie-Ashburn method in which it replaces Oil Red O. Those methods are used for staining lipids, triglycerides and lipoproteins on frozen histology sections.
The Sudan IV test will test positive for lipids. The test procedure involves adding a few drops of Sudan IV to the test solution. Sudan IV is a dye that will stain lipids. If no lipids are present then the dye will sink to the bottom of the test tube.
Sudan Black B is a diazo dye used for staining of neutral triglycerides and lipids on frozen sections and some lipoproteins on paraffin sections. It has the appearance of a dark brown to black powder with maximum absorption at 596-605 nm and melting point 120-124 °C. It stains blue-black
SUDAN IV FOR MICROSCOPY