Sudan IV (C₂₄H₂₀N₄O) is a lysochrome (fat-soluble dye) diazo dye used for the

staining Staining is a technique used to enhance contrast in samples, generally at the microscopic level. Stains and dyes are frequently used in histology (microscopic study of biological tissues), in cytology (microscopic study of cells), and in the ...

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 one of the dyes used for Sudan staining. Similar dyes include Oil Red O, Sudan III, and

Sudan Black B Solvent Black 3 is an azo dye. It is a non-fluorescent, relatively thermostable lysochrome (fat-soluble dye) diazo dye used for staining of neutral triglycerides and lipids on frozen sections and some lipoproteins on paraffin sections. It has the a ...

. Staining is an important biochemical technique, offering the ability to visually qualify the presence of the fatty compound of interest without isolating it. For staining purposes, Sudan IV can be made up in propylene glycol. Alternatively, authors have reported using the dye saturated in isopropyl alcohol, 95% ethanol, or 0.05% by weight in acetone:ethanol:water (50:35:15). The idea is to use a moderately apolar solvent to solubilize the dye allowing it to partition into the highly apolar fat without the solvent solubilizing the fat to be stained.

Sudan I Sudan I (also commonly known as CI Solvent Yellow 14 and Solvent Orange R), is an organic compound, typically classified as an azo dye. It is an intensely orange-red solid that is added to colourise waxes, oils, petrol, solvents, and polishes. Suda ...

, Sudan III, and Sudan IV have been classified as category 3 carcinogen by the International Agency for Research on Cancer. In its purified form it is called Biebrich scarlet R, which should not be confused with the water-soluble Biebrich scarlet. In industry, it is used to color nonpolar substances like oils, fats, waxes, greases, various hydrocarbon products, and acrylic emulsions. Sudan IV is also used in United Kingdom as a fuel dye to dye lower-taxed

heating oil Heating oil is any petroleum product or other oil used for heating; a fuel oil. Most commonly, it refers to low viscosity grades of fuel oil used for furnaces or boilers use for home heating and in other buildings. Home heating oil is often a ...

; because of that it is also known as Oil Tax Red. As a food dye, Sudan IV is considered an illegal dye, mainly because of its harmful effect over a long period of time, as it is a carcinogen. It was ruled unsafe in the 1995 food safety regulations report.

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Stains File
entry {{Stains Azo dyes Staining dyes Sudan dyes Fuel dyes IARC Group 3 carcinogens 2-Naphthols