What is the Difference Between Buffered Unbuffered and Neutralized Formalin?

Formalin is a common fixative used in histology and can be found in three major forms: buffered, unbuffered, and neutralized. The main differences between these forms are their pH and preservation capabilities.

1. Buffered Formalin: This is the standard and preferred formalin fixative for tissue preservation. It is typically purchased as a prepared solution and avoids the additional risks of handling needed to mix the buffered formalin solution from a stock solution. Buffered formalin is prepared by mixing one part of stock formalin with 9 parts of a buffer solution, usually sodium phosphate.
2. Unbuffered Formalin: This form is prepared by mixing one part of stock formalin with 9 parts of water, preferably distilled. Unbuffered formalin has a pH of 3-4, which can react with hemoglobin in the tissues to produce a dark brown acid, complicating histological interpretation.
3. Neutralized Formalin: This is a solution of formalin in water with a neutral pH value, typically 7.0. To adjust the pH of unbuffered formalin to a neutral value, a base such as sodium hydroxide is used. Neutralized formalin is less expensive and easier to prepare compared to buffered formalin.

In summary, the main differences between buffered, unbuffered, and neutralized formalin are their pH levels and the method of preparation. Buffered formalin is the preferred choice for tissue preservation due to its better preservation capabilities, while unbuffered and neutralized formalin show poor preservation of tissues.

Comparative Table: Buffered Unbuffered vs Neutralized Formalin

Here is a table comparing the differences between Buffered Formalin, Unbuffered Formalin, and Neutralized Formalin:

Buffered Formalin is the preferred fixative for tissue preservation due to its neutral pH and better tissue preservation properties. Unbuffered Formalin is less expensive and easier to prepare, but it shows poor preservation of tissues. Neutralized Formalin is a solution of formalin in water with a neutral pH value, but it also shows poor preservation of tissues.