Which statement about the pH adjustment of Mayer hematoxylin is correct?

• A. It is adjusted with citric acid
• B. It is adjusted with sulfuric acid
• C. It is not adjusted
• D. It is adjusted with acetic acid

Answer: (A)

The pH of Mayer hematoxylin is kept in an acidic, buffered range to promote the proper formation of the hematoxylin–mordant complex and to give crisp, uniform nuclear staining. Citric acid is a mild, buffering organic acid that provides that stable, slightly acidic environment without aggressively altering the solution or damaging tissues. This helps ensure consistent staining intensity and contrast, which is why citric acid is used for adjusting Mayer hematoxylin’s pH. If the pH weren’t adjusted, staining would vary from slide to slide; using a stronger acid could cause damage or over-staining.