An impeccable sample fixation is a prerequisite for a correct histological diagnosis. Tissue samples must be immersed in an optimally chosen fixative immediately after sampling because a timely fixation will prevent autolysis, putrefaction and other unwanted cellular changes. Although there are hundreds of histological fixatives and at least tens of formaldehyde-based fixatives, formaldehyde solutions with a concentration range from 4% to 10% are the most commonly used fixatives, primarily because of their simple and universal application. Tissue fixation using a formaldehyde solution results in forming cross-links, i.e. it forms methylene bridges between proteins, that is, it results in keeping tissue components in their in vivo relation. If fixated properly, the tissue sample can withstand additional histological tissue processing and staining.
The 4% formaldehyde solution is 10% formalin, which is the most commonly used fixative. It is suitable for fixating bioptic materials, smaller tissue samples and long-term fixated samples storing. It is a colorless solution with a characteristic odor, ready for applying. Added methanol prevents formaldehyde polymerization. It is a primary tissue fixative, and samples may be fixated and/or stored for a longer period of time without severe hardening of the tissue. It is suitable for usage in all automated devices for tissue processing, as well as for manual histological techniques. It is conveniently packaged in 1 liter bottles, 5, 10 and 20 liter canisters.