What is the Difference Between Formaldehyde and Paraformaldehyde?

The main difference between formaldehyde and paraformaldehyde lies in their chemical structure and usage:

• Formaldehyde is a small molecule that is a gas at normal conditions. It is the simplest aldehyde and is often used as a tissue fixative in histology and cell biology.
• Paraformaldehyde (PFA) is a polymer of formaldehyde, also known as polyoxymethylene. By itself, paraformaldehyde is not a fixing agent and needs to be broken down into its basic building block, formaldehyde, to be usable as a tissue fixative. This can be done by heating or basic conditions until it becomes solubilized. Paraformaldehyde is commonly used in research settings and can substitute 10% formalin.

Formalin is a saturated formaldehyde solution in water (37% by weight, 40% by volume) containing 10-15% methanol. Methanol is added to slow down the polymerization to formaldehyde, which reduces the fixing power of formalin. Formalin can also be made in an alcohol-free form from powdered paraformaldehyde. A protocol calling for 10% formalin is roughly equivalent to 4% formaldehyde.

In summary, formaldehyde is a gas used as a tissue fixative, while paraformaldehyde is a polymer of formaldehyde that needs to be broken down into formaldehyde to be used as a tissue fixative. Formalin is a saturated solution of formaldehyde with added methanol.

Comparative Table: Formaldehyde vs Paraformaldehyde

Formaldehyde and paraformaldehyde are both types of aldehydes used in various applications, such as cell fixation in immunohistochemistry and fluorescent protein labeling. Here is a table summarizing the differences between the two:

Paraformaldehyde is a polymer of formaldehyde and is not a fixing agent itself. When dissolved in water or a buffer, it breaks down into formaldehyde, which is the actual fixing agent. Both formaldehyde and paraformaldehyde can be used as fixation solutions for immunohistochemistry and fluorescent protein labeling.