Flawless specimen fixation is a prerequisite for correct histological diagnosis. Tissue samples should be immersed in an optimally selected fixative immediately after sampling, as timely fixation will prevent autolysis, decay, and other unwanted cellular changes. Although there are hundreds of histological fixatives and at least dozens of formaldehyde fixatives, neutral buffered formaldehyde solutions ranging from 4% to 10% are the most commonly used fixatives, primarily because of their simple and versatile use. Fixation of tissue with a buffer solution of formaldehyde leads to the formation of cross-links, that is, it forms methylene bridges between proteins, that is, it preserves tissue components in their ratio in vivo. With proper fixation, the tissue sample perfectly withstands additional histological tissue processing and staining.

10% neutral buffered formalin, intended for
use as a fixative in the processing of biological tissues or clinical specimens. It is a ready-to-use, colorless solution with a characteristic odor. It is possible to manufacture with a bluish or pinkish tint. The addition of phosphate buffer prevents the formation of formalin pigment. PH range 6.8 - 7.4. Added methanol prevents formaldehyde polymerization