Re: formalin at 4C and shelf life

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Date:Fri, 6 Aug 1999 08:44:50 -0400
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---------------------- Forwarded by Rande Kline/EMI/Merck on 08/06/99 08:42
AM ---------------------------

Rande Kline
08/05/99 08:27 AM

Subject:  Re: formalin at 4C and shelf life

Sorry,  I was editing the address when I accidentally hit send before I was
finished.  Unfortunately, you may have received the unfinished one twice.
But I have added other information.

This conversation really had me busy. This is a long one.

---------------------- Forwarded by Rande Kline/EMI/Merck on 08/04/99 12:14
PM ---------------------------

Rande Kline
08/04/99 12:14 PM

Subject:  Re: Shelf life of 4% formaldehyde solutions  (Document link not

 Formaldeyhyde has the methanol additive for stabilization which would
carry over into the 10% formalin when prepared.  This would be true even if
purchased prepared.,

We used 10% formalin fixed tissue on paraffin sections for IHC with no ill
effects unless the procedure called for a different fixation such as frozen
sectioning.  The important part here, is to not let the tissue overfix in
10% formalin.

A good recommendation for determining expiration on all chemicals would be
too look at the MSDS sheet for decomposition information.  My suggestion
would be to try to obtain an MSDS from a manufacturer who is producing 4%

Always follow the manufacturer storage recommendations.  This is important.

About freezing temperatures. Chemicals do have freezing points. Many are
not compromised if they reach the freezing points.  They just need to be
thawed.  This could be accomplished by submerging them in water above their
freezing point or  they can be thawed by room temperature.  Also, many
people do not realize that room temperature may be freezing points for some
chemicals. If chemicals are received frozen or looking cloudy, call the
manufacturer for information on thawing.  Always make sure lids are
loosened when thawing.

Information on freezing points may be found in various references such as a
Condensed Chemical Dictionary or Lange's Handbook Of Chemistry.

I do not have  any research information on NBF freezing ( I can't believe
I've never received a call on this one).   I did hold my own little forum
here. I can't see how this would be unusable.  Basically, freezing just
changes the form of things not necessarily the composition.  When water
freezes, the composition doesn't change the form does.  Thawed it goes back
to water.  I think the same pertains to NBF.  Change the temperature the
salts and the formaldehyde will  precipitate and perhaps the solution will
be cloudy.  Thaw and it's back to NBF.

I looked in various references.  The by-product of formaldehye is
paraformaldhyde which as Gayle stated is caused by polymerization
According to the Merck Index  paraformaldehyde is slowly soluble in water
and very soluble in hot water.  It's would be a good idea to avoid the hot
water part.  Too dangerous.  Salts could also change form upon freezing.
Theoretically, all should go back into solution.  How long it takes would
be explained by latent infusion which is the difference between liquid and
solid states.

I would be interested in others comments.

Rande Kline HT (ASCP)
Technical Services
EM Science

"Karen D. Larison" <> on 08/03/99 09:11:48 PM

Subject:  Re: Shelf life of 4% formaldehyde solutions


Formalin has additives such as methanol to keep the formaldehyde from
polymers and precipitating from solution.  Therefore its shelf life is
longer than
pure formaldehyde.  Most people avoid using formalin-based fixatives when
IHC, simply because additives such as methanol may have an adverse affect
on the
epitope.  Most people instead use a 4% paraformaldehyde solution made up
fresh in a
phosphate buffer.  The shelf-life on this quite short.  You'll notice
forming in this fixative in about a week, even when stored refrigerated.

Karen in Oregon

Date:          Tue, 3 Aug 1999 13:51:11 -0500
From:          "LOVE, JOHN E. (JSC-SD)" <>
Subject:       Shelf life of 4% formaldehyde solutions
To:            "''"

I understand that the shelf life of formaldehyde solutions is affected by a
variety of reactions including oxidation, methanol formation,
polymerization, and condensation.  I am interested in finding out about the
shelf life of buffered 10% formalin (4% formaldehyde) solutions stored at 4
degrees C.
Thank you for your help.

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