[Histonet] RE: pfa vs. formalin

[Bryan Hewlett]

Melissa,

There is NO such thing as a solution of paraformaldehyde.
As has been stated many times, paraformaldehyde is a solid polymerized form 
of formaldehyde.
When paraformaldehyde is dissolved in water, it de-polymerizes to form 
formaldehyde.
The formaldehyde in turn hydrates to become methylene glycol.
10% NBF is, for all practical purposes, the same whether made from 
commercial formalin (37-40% formaldehdye) or from solid paraformaldehyde.

Bryan

----- Original Message ----- 
From: "Melissa Gonzalez" <Melissa.Gonzalez <@t> cellgenesys.com>
To: <jdr43 <@t> omega.med.yale.edu>
Cc: <histonet <@t> lists.utsouthwestern.edu>
Sent: Friday, August 04, 2006 2:03 PM
Subject: [Histonet] RE: pfa vs. formalin


Hi Jason,
I was taught by histotechs that 10%Neutral Buffered Formalin is the gold 
standard vs paraformaldehyde, because it is optimally buffered to exchange 
with tissue fluids during the fixation process, and that unbuffered 
fixatives can result in artifacts which you may find microscopically in the 
tissue slices after stainings. How major/minor this detail turns out overall 
in the grand scheme of things, I don't really know. I've never seen the 
direct compare and contrast, for example in H&E sections comparing both 
fixatives.
I have found a supplier of 10% Buffered Paraformaldehyde, from Newcomer 
Supply, which I use routinely for immunofluorescence of perfused, and 
cryoprotected samples.
So then I would like to know, is there a technical difference between 10% 
NBF (formalin) vs 10% NBP (paraformaldehyde)?

thanks
Melissa
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