Yes, we would say that heating is not necessary to depolymerize PFA. Only
the high pH is.
After 30-60 minutes of stirring we obtain a crystal clear solution with
only a few particles of undissolved PFA swimming around at the bottom
(which is why we filter).
--On Monday, December 08, 2008 9:19 AM -0700 [EMAIL PROTECTED] wrote:
Hi Merced,
Thanks for your reply. So then you manipulate pH rather than temperature
to ensure the dissolution of PFA. Does dissolution also mean that the PFA
has depolymerized? Are you saying heating to 60 degrees C is not required,
or that it is not recommended? I've been told that heating 'degrades' the
PFA and one wants to avoid this. But according to other sources, the
heating step is required to ensure that the PFA does in indeed degrade,
degrade into formaldehyde.
Eric
University of Calgary
Medical Sciences
We routinely add paraformaldehyde to alkaline water at room temperature
while stirring and wait only about 30-60 mintues for it to dissolve.
Then we add a concentrated amount of PBS up to the total required volume
(so that the buffer is 1x in the final volume). Then we add acid to
bring the pH back down to 7. Then we filter it since not all of the PFA
has dissolved (though most of it has).
Merced
--On Monday, December 08, 2008 9:11 AM +1100 Tony Henwood
<[EMAIL PROTECTED]> wrote:
My experience is that when you add paraformaldehyde to water all it
forms is a colloidal solution (ie on standing, the paraformaldehyde
settles with very little going into solution (personal experience,
waited one week, then gave up).
Has your experience been different?
Regards
Tony Henwood JP, MSc, BAppSc, GradDipSysAnalys, CT(ASC)
Laboratory Manager & Senior Scientist
Tel: 612 9845 3306
Fax: 612 9845 3318
the children's hospital at westmead
Cnr Hawkesbury Road and Hainsworth Street, Westmead
Locked Bag 4001, Westmead NSW 2145, AUSTRALIA
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
[EMAIL PROTECTED]
Sent: Sunday, 7 December 2008 7:30 AM
To: histonet@lists.utsouthwestern.edu
Subject: [Histonet] PFA preparation
Hi,
So then what is the best way to prepare formaldehyde fixative from
PFA?
The way I have been taught, which differs from what I have read, is
to dissolve 4% into ddH2O at room temperature. After that one could add
PBS or buffer.
I've also been taught that too much heat during preparation
"degrades" PFA, and that PFA (or formaldehyde solution, rather) stored
too long will lose freshness because it "degrades."
What I read is different. Texts suggest to dissolve the PFA in warm
water, and that aging of the fix is due to repolymerization, not
through
degradation.
What should i do?
Eric Schmidt
University of Calgary
Medical Sciences
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Merced M Leiker
Research Technician II
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School of Medicine and Biomedical Sciences
State University of New York at Buffalo
3435 Main St, Buffalo, NY 14214
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"Without my flaws I'm really very boring."
- random internet blog commentator
Merced M Leiker
Research Technician II
354 BRB (pkgs) / 140 Farber Hall (letters)
School of Medicine and Biomedical Sciences
State University of New York at Buffalo
3435 Main St, Buffalo, NY 14214
Ph: (716) 829-6033
Fx: (716) 829-2725
"Without my flaws I'm really very boring."
- random internet blog commentator
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