[Histonet] Silly Question?

Geoff McAuliffe mcauliff <@t> umdnj.edu
Thu Dec 11 14:53:12 CST 2008

Hi Pat:

    The differences are largely in the minds of the investigators. 
Confusion comes from inexact nomenclature. One part of formaldehyde 
(37-40%) plus 9 parts of buffer makes formalin or 10% formalin which is 
about 4% formaldehyde. Yes, the 37-40% formaldehyde you buy has some 
methanol added to keep it from polymerizing but it makes no difference 
in the quality of fixation, especially given the (too) short times used 
to fix clinical specimens. Sure, you can go to the trouble to make 4% 
formaldehyde solution fresh from paraformaldehyde but for the vast 
majority of applications it just does not matter.


Pat Flannery wrote:
> Please humor me on this if it's obvious (to everyone but me):  why do 
> we use paraformaldehyde (which is so inconvenient to make up) rather 
> than buffered formalin or just diluted formaldehyde itself?
> It seems that around here, some folks prefer paraformaldehyde (either 
> 2% or 4%) and others use formalin, while some others stick to diluted 
> formaldehyde (I see all 4 on labels for specimens submitted for 
> histology).  Is it mostly a matter of personal preference or where you 
> were trained (i.e. force of habit) or is there a valid reason to use 
> each solution (basically the same chemical once in solution, merely 
> buffered or not)?  The only answer I've gotten when I've asked is, 
> "That's what we always use."
> Thanks.
> -Pat Flannery (not a "real" histologist - I just play one in the lab)
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Geoff McAuliffe, Ph.D.
Neuroscience and Cell Biology
Robert Wood Johnson Medical School
675 Hoes Lane, Piscataway, NJ 08854
voice: (732)-235-4583 
mcauliff <@t> umdnj.edu

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