[Histonet] PFA preparation: Does dissolution also mean that the PFA has depolymerized?

[Merced Leiker]

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 ejschmid <@t> ucalgary.ca 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
>> <AnthonyH <@t> chw.edu.au> 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: histonet-bounces <@t> lists.utsouthwestern.edu
>>> [mailto:histonet-bounces <@t> lists.utsouthwestern.edu] On Behalf Of
>>> ejschmid <@t> ucalgary.ca
>>> Sent: Sunday, 7 December 2008 7:30 AM
>>> To: histonet <@t> 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
>> 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
>>
>>
>>
>
>
>



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