Which mordant salt is used to make Hematoxylin solutions most commonly used in routine H&E?

• A. Aluminum
• B. Iron
• C. Copper
• D. Magnesium

Answer: (A)

The main idea is that hematoxylin must form a stable complex with a mordant to stain nuclei effectively. Hematoxylin is first oxidized to hematein, and the mordant serves as a bridge between hematein and the tissue, especially binding to the negatively charged components of the nucleus. Aluminum mordants are the standard choice in routine H&E because the hematoxylin-aluminum complex binds strongly to nuclear material and produces a crisp blue-to-purple nuclear stain that remains stable during processing and is compatible with the eosin counterstain. Other mordants can alter the hue or stability of the staining—for example, iron mordants tend to give brown-black tones and are used in different stain variants, while copper or magnesium mordants are not typical for standard H&E.