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

[ejschmid <@t> ucalgary.ca]

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
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