What is the Difference Between Formalin and Formaldehyde?

Formaldehyde, formalin, and paraformaldehyde are related substances used in various applications, but they have different properties and compositions. Here are the main differences between them:

1. Formaldehyde: Formaldehyde is a small molecule that is a gas at normal conditions. It is the simplest aldehyde and is used extensively as a precursor for more complex resins, such as melamine and urea formaldehyde resins.
2. Formalin: Formalin is a ~40% saturated solution of formaldehyde. It is composed of three components: formaldehyde, methanol, and water. Formalin is widely used as a disinfectant, germicide, and for preventing cell decay. It is also the most common chemical fixative used in histopathology, providing excellent preservation of tissues' morphology. A 10% formalin solution is roughly equivalent to 4% formaldehyde.
3. Paraformaldehyde: Paraformaldehyde consists of polymers of formaldehyde and is a white crystalline powder. It can be purchased in solid form and diluted to prepare a 4% paraformaldehyde solution in PBS, which is commonly used in research settings and can substitute 10% formalin. Paraformaldehyde is often used in electron microscopy (EM) preparations.

In summary, formaldehyde is a gas that serves as the base substance for formalin and paraformaldehyde. Formalin is a saturated solution of formaldehyde containing methanol and water, while paraformaldehyde is a solid polymer of formaldehyde. All three substances have different applications and can be used as fixatives in histopathology, but they vary in composition and form.

Comparative Table: Formalin vs Formaldehyde

Here is a table summarizing the differences between formalin, formaldehyde, and paraformaldehyde:

Please note that these terms are often used interchangeably, and there can be confusion in their definitions. The table above aims to provide a clear distinction between the three terms based on their standard definitions and common usage.