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Toluidine Blue O

Toluidine Blue O

Class: Thiazin
Ionisation: Basic

Chemical structure of Toluidine Blue O

Common Name: Toluidine blue
Suggested Name: Toluidine blue O
Other Names:

Tolonium chloride

C.I. Number: 52040
C.I. Name: Basic blue 17
Color: Blue
Solubility Aqueous: 3.82%
Solubility Ethanol: 3.82%
Absorption Maximum: 620-622 (Conn) 632 (Gurr) 640.4 (Merck) 626 (Aldrich)
Empirical Formula: C15H16N3SCl
Formula Weight: 305.8


Toluidine blue O is a metachromatic dye, and is frequently employed in that capacity. It is a blue nuclear counterstain, and can be used to demonstrate Nissl substance. It is useful for staining mast cell granules, both in metachromatic and orthochromatic techniques. Compare its formula to other methylene blue homologues.


  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.
  4. Susan Budavari, Editor,
    The Merck Index, Ed. 12
    Merck & Co., Inc., Whitehouse Station, NJ, USA