What chemical changes hematoxylin to hematein in staining procedures?

• A. Sodium iodate
• B. Ammonium aluminum sulfate
• C. Ferric chloride
• D. Sodium chloride

Answer: (A)

The activating step is oxidation: hematoxylin must be converted to hematein to become the active form that forms a colored complex with a mordant and binds in nuclei. Sodium iodate serves as the mild oxidizing agent that turns hematoxylin into hematein in the staining solution. Once hematein is formed, it chelates with a metal mordant such as aluminum or iron to create the intensely colored nuclear stain. The other substances listed act as mordants (aluminum or iron) or are simply unrelated salts (sodium chloride) and do not convert hematoxylin to hematein.