RE: [Histonet] formalin nomenclature

From:"Barry R Rittman"

While formalin solutions contain methanol, it is usually present in
around 5% concentration. It is there to act as a reducing agent so that
formalin does not become oxidized to formic acid. Once 10% formalin
solution is made from the stock formalin solution, the concentration of
the methanol is negligible and I do not believe would interfere with the
fixing effect of the formalin.  The use of phosphate buffering solution
essentially eliminates the effects of any formic acid.
As Freida has pointed out it is a pain to have to make solution up from
scratch, dealing with paraformaldehyde powder etc. If expense is a
secondary consideration, and especially for electron microscopy, some
companies (I believe Ladd) sell ampoules of pure formalin that is sealed
under nitrogen and you merely have to break open the vial and dilute.

-----Original Message-----
[] On Behalf Of
Sent: Wednesday, July 21, 2004 8:41 AM
Subject: Re: [Histonet] formalin nomenclature

The primary difference is that commercial 37-40% formaldehyde solutions 
contain some methanol; whereas, the paraformaldehyde solutions do not.
This has 
been considered an important difference especially for electron
microscopy, and 
possibly some other applications.  Formalin solutions prepared from 
paraformaldehyde are purer solutions, but unless you need the purity,
they are much more 
difficult to prepare.

Freida Carson
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