Dear John,
I've just finished trialling Conc. Formalin, a new variant from Orica
Chemical (Formerly ICI) which has a lowered methanol content and uses a
patented anti-polymerisation agent. We stored this at 4C for 8 months in a
coolroom and no turbitiy was detected, assay by w/v revealed was still at
40.3%. They are now trying to find a way of introducing the process into
their plants for mass production.
On the issue of 4% Neutral buffered material (Using sorensen salts as in
Bancroft and Stevens, Carleton etc.) I have assayed material at one and two
years @ 4C and found there to be no detectable polymerization and the conc.
of Formaldehyde still within specs viz. 4.0+-.02%.(Using Peroxide/ Hydroxide
Titre). At RT stored solutions I have found no deterioration at five years,
although solutions kept in sunlight for 2 yrs did show decolorisation of any
indicators present (we only tried Bromothymol Blue and Bromocresyl Purple)
even though the pH was still 7.0=- 0.1 and the formaldehyde assay was fine.
You should note that the situation is of course different for actual tissues
stored in such solutions- to alert lab staff to early pH changes in stored
specimens, we have for the last 15 years or so only used NBF with
Bromothymol Blue Indicator in it, so that as soon as a slight yellow colour
change is detected the solution is replaced. My experience is that the time
this will take to happen for various tissie types also varies until the
material is fully fixed, eg. Blood filled tisses such as spleen, liver,
placenta etc, may have to be replaced several times in the first week,
whereas knee joint cartilage is fine even after two years in the dark.
PS. I have no interest in Orica, they merely asked us to trial the material
because of our large turnover of Formaldehyde ie. 1500-2000 litres/month. If
you use an indicator system, we have found no adverse effects on IPX either.
Hope this helps in some way.
Regards Mike Rentsch (Downunder)
-----Original Message-----
From: LOVE, JOHN E. (JSC-SD) <john.e.love1@jsc.nasa.gov>
To: 'histonet@pathology.swmed.edu' <histonet@pathology.swmed.edu>
Date: Wednesday, 4 August 1999 7:23
Subject: Shelf life of 4% formaldehyde solutions


>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.
>                                    John
>
>