Paraformaldehyde shelf-life?

Terence P. Ma tpm at anat.UMSMED.EDU
Sat Oct 23 17:38:27 EST 1993

In article 656 at, anon1167 at (M) writes:
>I was recently told that, when using paraformaldehyde for 
>perfusion, the P must be made immediately prior to perfusion.
>I have been doing perfusions for years with para made up
>to several days prior to the perfusion.  The people who 
>have told me this don't seem to have a good reason _why_ you
>need to make the stuff up right away.  Does para have a 
>short shelf life?  Does "old" para react differently with tissue? 
>(In this case, neural tissue?)  A

I'm neither chemist nor theorist. I generally think of paraformaldehyde
as high grade formaldehyde. It breaks down into formic acid and water
over time (I think). Thus, the concentration is not as good.

Personal experience, for best results:

For general neural tissue for Nissl or fiber staining (Weil or
Gallyas), I use 10% buffered formalin (purchased in solution form and
in bulk from Sigma).

If I want to do something fancier, like cytochrome oxidase stain, I use
4% paraformaldehyde, 0.1% glutaraldehyde in 0.1 M phosphate buffer. I
will use other combinations for various tracers or

I try to always use glutaraldehyde for E.M. material (E.M. grade
glutaraldehyde not necessary if the bottle if biological grade 50% glut
is fresh).

Anytime I make up paraformaldehyde fixes, they just don't seem as good
if they've sat for more than 24-48 hours. The results are similar to
having taken the paraformaldehyde above 60 deg C when making it up.

So, in sum, if you must use paraformaldehyde (which should only be
handled inside a vented hood), then use it ASAP.

Terence P. Ma, Ph.D.            Department of Anatomy
VOICE:     601-984-1654         University of Mississippi Med. Ctr.
FAX:       601-984-1655         2500 North State Street
INTERNET:  tpm at anat.UMSMED.EDU  Jackson, MS 39216-4505

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