Polymethanal (paraformaldehyde)

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Polymethanal is a common fixative in biology. It is used to reduce degradation in cells, tissue and entire organisms before further experiments, e.g. antibody staining.

Too many names

There's plenty of confusion regarding this chemical because too many synonyms exist. Paraformaldyhde is probably still the most common term among biologist, but it ignores attempts to introduce meaningful and systematic names in chemistry. Polymethanal is clearer: poly - polymer, meth - single carbon, -al - aldehyde group.

Here's a list of equivalent terms: polymethanal, polyoxymethylene, polyformaldehyde, paraformaldehyde, paraform, polytrioxane,.. (regards from Babel)

CAS number = 30525-89-4

Comparison with methanal

Polymethanal is often preferred over methanal which is also used in fixation of live material. This is because polymethanal is a solid which makes it easier to transport and a little safer to use. The chemistry of fixation is similar due to the partial depolymerisation of polymethanal in the buffer making process (basic hydrolysis).

Chemistry of fixation

The aldehyde group, especially of methanal, is very reactive. It readily combines with amino groups to amides or with alcohol groups to esters. These reactions are mostly irreversible. Unreacted molecules have to be removed prior to subsequent experiments since they easily damage proteins like antibodies.

Recipes for polymethanal buffers

4% PFA

Polymethanal safety data sheets