Which chemical oxidizes hematoxylin to hematein during preparation?

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

Answer: (A)

Hematoxylin must be converted to its active form, hematein, before it can bind properly in the stain. The oxidizing agent used to make this conversion in many hematoxylin protocols is sodium iodate. Once hematoxylin is oxidized to hematein, it forms a colored complex with the aluminum mordant (often supplied as ammonium aluminum sulfate) that binds to tissue structures, especially nuclei, producing the characteristic blue-black stain. Ferric chloride can act as a mordant in some contexts but is not the standard oxidizer for hematoxylin. Methyl green isn’t involved in this oxidation step, and ammonium aluminum sulfate serves as the mordant rather than the oxidizer.