Glyoxal is best used at which pH?

• A. pH 4
• B. pH 7
• C. pH 9
• D. pH 2

Answer: (A)

Glyoxal fixatives rely on aldehyde cross-linking of tissue proteins, and this chemistry works best under acidic conditions. At around pH 4, glyoxal remains reactive enough to form stable cross-links with amino groups on proteins, which preserves tissue morphology effectively and yields reliable staining after processing. If the pH is neutral or basic, glyoxal tends to become less reactive or polymerize, leading to weaker fixation and poorer preservation of structure. On the other hand, very strong acidity (near pH 2) can damage tissue integrity and introduce artifacts. Therefore, buffering glyoxal fixatives to about pH 4 provides the best balance for proper fixation.