In Harris' Hematoxylin, which component acts as the mordant?

• A. Ammonium aluminum sulfate
• B. Ferric Chloride
• C. Mercuric Oxide
• D. Sodium iodate

Answer: (A)

In hematoxylin staining, the mordant is the metal salt that forms a stable dye-tissue complex (a lake) so the stain stays fixed in the tissue. For Harris’ hematoxylin, the mordant is the aluminum salt provided by ammonium aluminum sulfate. This aluminum ions bind with the oxidized form of hematoxylin (hematein) to create a lake that adheres well to nuclear material, producing the characteristic crisp, blue-black nuclear stain.

The other reagents in the mix mainly serve as oxidizing agents or aids in color development rather than forming the dye-tissue lake themselves. Sodium iodate and mercuric oxide act as oxidizers to convert hematoxylin to hematein, enabling the lake to form, while ferric chloride is used in different hematoxylin formulations (such as iron-based variants) as mordant or oxidizer depending on the protocol, but not the component acting as the mordant in Harris’ formulation.