Formaldehyde pH for Northerns?

Henk Veldman H.Veldman at
Thu Apr 6 03:52:22 EST 2000

pathos schreef:

> In article <8cgd09$si$1 at>, "Gys de
> Jongh" <GysdeJongh at> wrote:


> > The formaldehyde will be converted to formic acid by air oxigen.
> I do not think this is true either.  I am no organic chemist but I believe
> that Formaldehyde which is a gas (bp -21C)  at room temperature can be
> dissolved into water to form a solution.  The solution that I and others
> buy is a 37% aqueous solution that is often called formalin.  In the
> solution of Formalin, Formaldehyde reacts with water via a hydration
> reaction to form Methanediol not to be confused with Methanoic acid
> (formic acid).  It is one of the few carbonyl compounds that exsist almost
> exclusively as a hydrate in solution.
> The reason that the running buffers pH will drop has more to do with
> elctrochemistry.  I personally have never found formaldehyde to be the
> culprit of poor quality RNA but maybe I have not done enough Northerns yet
> --
> Peter Pediaditakis
> University of Pittsburgh
> Dept. of Pathology

Straight formalin (35 - 37 % formaldehyde solution) will turn *bad* on prolonged
storage. Two formaldehyde molecules will react to form methanol and formic acid.
This reaction can be retarded by adding methanol (some commercial preparations have
about 10 % methanol added), or the acid can be captured (other commercial
preparations have a slurry of some acid-binding substance on the bottom). Storing in
the cold might slow the breakdown of the formaldehyde, it will also increase the
polymerization to paraformaldehyde, especially when the solution is acid.
Usually formalin is diluted into some buffer before use, which will take care of pH.
However, for very critical applications it is still best to prepare a fresh solution
from paraformaldehyde.

Regards, Henk

H. Veldman
Laboratory for Experimental Neurology (NMZ)
Room G 02.320
University Medical Center Utrecht (AZU)
P.O. Box 85500
The Netherlands
Tel: +31 30 2507565
Fax: +31 30 2542100
E-mail: H.Veldman at

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