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Sirius Red 4B

Sirius Red 4B

Class: Azo
Ionisation: Acid

Chemical structure of Sirius Red 4B

Common Name: Sirius red 4B
Suggested Name: Sirius red 4B
Other Names:

Chlorantine fast red 5B

C.I. Number: 28160
C.I. Name: Direct red 81
Color: Red
Solubility Aqueous: Moderate
Solubility Ethanol: Moderate
Absorption Maximum: 508 (Aldrich), 502 (Gurr)
Empirical Formula: C29H19N5O8S2Na2
Formula Weight: 675.62


Sirius red 4B has been recommended as the plasma stain in some trichrome staining methods, or as a substitute for acid fuchsin in the van Gieson.

It is sometimes confused with the similarly named dye, sirius red F3B, which may be used for demonstrating amyloid. Sirius red 4B is not used for that purpose and is not a substitute for congo red.


  1. R. D. Lillie.
    Conn’s Biological Stains
    Williams & Wilkins, Baltimore, MD., U.S.A.
  2. Aldrich chemical catalogue, 1992
    Aldrich Chemical Company, Milwaukee, WI, USA.
  3. Edward Gurr, 1971
    Synthetic dyes in biology, medicine and chemistry
    Academic Press, London, England.