Which statement is true about buffering formaldehyde solutions with monobasic and dibasic sodium phosphates?

• A. They help maintain pH during fixation
• B. They accelerate fixation dramatically
• C. They sterilize the solution
• D. They change the color of the tissue

Answer: (A)

Maintaining pH during fixation is essential when formaldehyde solutions are buffered with monobasic and dibasic sodium phosphates. The phosphate buffer holds the solution near neutral pH, which prevents acidification that can occur as formaldehyde reacts and forms formic acid. A stable, near-neutral pH helps ensure consistent crosslinking of proteins, preserving tissue morphology and making staining and interpretation more reliable. Buffering does not dramatically speed fixation, does not sterilize the solution, and does not change tissue color, so the statement about maintaining pH best fits the purpose of using these phosphates.