formalinen

Formalin is an aqueous solution of formaldehyde, typically containing about 37% formaldehyde by weight in water and stabilized with small amounts of methanol to slow polymerization. The term is commonly used to refer to this solution, though it can also describe related formaldehyde solutions used for preservation and disinfection.

Formaldehyde, also called methanal, is a colorless gas at room temperature that is highly soluble in water. In water it exists mainly as methylene glycol and can form various polymeric species. In practice, stability and handling concerns lead to the use of stabilized solutions rather than pure formaldehyde gas.

Common variants include neutral buffered formalin, where formalin is adjusted to near-neutral pH with phosphate buffers. A widely used preparation is 10% neutral buffered formalin, which contains about 3.7–4% formaldehyde and is standard for tissue fixation in histology and pathology.

Uses of formalin are broad. It is the primary fixative for preserving biological tissues, enabling subsequent microscopic examination. It is also used in disinfection and sterilization, embalming, and in certain industrial processes such as the production of resins and textiles. Because formaldehyde can cross-link proteins, tissues fixed in formalin retain structural details but may require special processing for molecular analyses.

Safety and regulation are important considerations. Formaldehyde is toxic and is classified by many authorities as a human carcinogen. Exposure can irritate the eyes, nose, and throat, and long-term exposure is associated with cancer risk. Work with formalin is conducted in well-ventilated areas or fume hoods, with appropriate protective equipment and strict handling and disposal procedures in accordance with local regulations. Storage requires tightly closed containers and protection from heat and incompatible materials.