Hematein formation can be promoted by exposure to which factor?

• A. Air
• B. Formaldehyde
• C. Aluminum salts
• D. Water

Answer: (A)

Hematein is the active, oxidized form of hematoxylin that binds to tissue when it forms a complex with a mordant. The oxidation step is driven by atmospheric oxygen, so exposure to air provides the necessary oxidant to convert hematoxylin into hematein. Once hematein is formed, it then coordinates with a mordant like aluminum to create the stain. Water is only a solvent, and while it keeps the solution hydr­ated, it doesn’t drive oxidation. Formaldehyde is a fixative and doesn’t promote hematoxylin oxidation. Aluminum salts act as mordants after hematein formation, not as the oxidizing agent. So, exposure to air best promotes the formation of hematein.