Which chemical is used in the prep of Weigert's hematoxylin?

• A. Ferric chloride
• B. Ammonium aluminum sulfate
• C. Sodium hydroxide
• D. Acetic acid

Answer: (A)

Ferric chloride provides the iron mordant that forms a stable hematoxylin lake. In Weigert's hematoxylin, the iron from ferric chloride binds to hematoxylin, creating a complex that strongly adheres to nuclear material and develops the characteristic dark blue-black nuclear stain after oxidation and bluing. This mordanting step is essential for the durability and intensity of the stain. The other chemicals listed aren’t used as the mordant in this prep—aluminum salts appear in other hematoxylin formulations, while sodium hydroxide or acetic acid are more about pH adjustments or differentiation in different protocols.