At 19:57 22/01/01 -0500, vous avez écrit:
>On Tue, 23 Jan 2001, Jane Radford wrote:
>
> > Can Periodate lysine paraformaldehyde fixative be frozen?
>
>You should not freeze any solution containing formaldehyde.
>Low temperatures (even without freezing) accelerate
>polymerization and a white precipitate of paraformaldehyde
>forms in the bottle. This lowers the concentration of
>dissolved formaldehyde (which may not matter much) and
>gets insoluble paraformaldehyde onto and sometimes also
>within the specimen. This remains there and can make for
>difficult sectioning.
>
>Two of the ingredients of PLP (lysine and formaldehyde)
>react chemically when mixed, so the working fixative
>solution should be made immediately before use. You
>can make concentrated stock solutions (lysine, sodium
>periodate, phosphate-buffered formaldehyde) and mix these
>when needed. There is no advantage in keeping the stock
>solutions cold (except possibly the lysine, which might
>get infected).

Hi,

I obviously agree with John Kiernan on the paraformaldehyde and storing 
formaldehyde solutions in the cold. We use PLP fixative a lot, and we store=20
the lysine-phosphate buffer frozen for cell cultures. For perfusion 
fixation, we always make up the buffer fresh, given the amounts needed. We=20
noticed that after about 3-4 days in the fridge, precipitates start to 
appear in this lysine-phosphate buffer. The frozen lysine buffer on the 
other hand has never failed us.

We prepare the fixative immediately before use by mixing 3 vol lysine 
phosphate buffer and 1 vol 8 or 16 % formaldehyde (depending on the desired=20
final concentration of formaldehyde). The periodate is also added as a 
powder just before use, but needs some vigorous stirring to dissolve. We've=20
had some problems with a 200 mM periodate stock solution, thus we went back=20
to the powdered form.

Storing the lysine-phosphate buffer frozen appears to be the most 
convenient, because in the preparation of PLP fixative it's the preparation=20
of this buffer that is the most time-consuming. Stocks of formaldehyde are=20
usually at hand and weighing the appropriate amount of periodate does not 
require much time (unless you have to start by cleaning the balance left 
... untidy by some coworkers :o/ )

Paul
                                                                         -=3D-
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==========================3D=====oOo==(_)==OOo=============3D================
Paul Klosen, PhD
CNRS UMR 7518 Neurobiologie des Fonctions Rythmiques et Saisonnieres
Universite Louis Pasteur  12, rue de l'Universite
F-67000 Strasbourg, FRANCE
Tel. 03.88.35.85.04  Fax. 03.88.24.04.61
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