What is an advantage of buffered picric acid-formaldehyde fixation (PAF, Zamboni's)?

• A. Specimens may remain in the fixative indefinitely.
• B. It provides the best lipid preservation.
• C. It prevents lipid extraction.
• D. It is incompatible with light microscopy.

Answer: (A)

The main idea here is that this buffered fixative creates a stable environment that can preserve tissue for a long time. Zamboni’s solution combines picric acid and formaldehyde in a buffered medium, so the pH stays near neutral and the tissue is rapidly fixed by crosslinking of proteins. This combination inhibits decay and autolysis enough that specimens may be left in the fixative for extended periods—indeed, indefinitely in practical terms—without losing morphology. That long-term stability is especially useful when processing needs to be delayed or when samples arrive in batches, because you can fix them and store them safely until you’re ready to proceed.

Lipid preservation is not the standout advantage of this fixative; picric acid-containing fixatives can actually alter or extract lipids, so that isn’t why this method is favored. And this fixative is compatible with light microscopy, so the claim that it isn’t is not correct either.