I don't think it reverts to regular formaldehyde - I'm not even sure what
that means. What does happen, though, is that dilute formaldehyde gradually
turns into formic acid. The reason to use paraformaldehyde, and to make it
up fresh in small quantities, is that then you can be sure your solution
*is* formaldehyde, rather than partly acid. Another way to ensure this is to
use 37% formaldehyde (or formalin - two words for the same thing) and dilute
it to your required concentration each time you use it. Even so, you should
replace the 37% after a year or so. Hope this helps.

Lesley Weston.


on 20/05/2002 11:52 AM, Atoska S. Gentry at gentras@vetmed.auburn.edu wrote:

> 
> Dear All, will someone please provide me information on the shelf life of
> 4%PFA/PBS?  I have a few liters of this unused fixative left over from
> various experiments.  And I'm wondering if it can be used for routine
> fixation or if I should just treat it for waste disposal?  A couple of
> years ago I heard by word of mouth that after a certain period of time the
> PFA reverts back to  regular formaldehyde.  Does anyone have a reference
> you can recommend whereby I can get my questions answered?  On the other
> hand if you know for a fact that it can be used as  either formaldehyde or
> 10% formalin please will you share this info with me?  If it can be used
> does it need to be stored at 4C?  Thanks, Atoska
> 
> 
> 
> 
> 
> 
> Atoska S. Gentry B.S., HT(ASCP)
> Research Assistant III
> Scott-Ritchey Research Center
> College of Veterinary Medicine
> Auburn University, AL  36849
> Phone# (334)844-5579  Fax# (334)844-5850
> 
>