Kelly,

Vapour fixation, mainly with  formaldehyde and osmium fixatives is a
practice of long standing (1944?) in histology and cytology.
It has also been applied to freeze dried tissues. Probably the most famous
application was by Falck (1962) who described vapour fixation at elevated
temperatures with formaldehyde and the subsequent conversion of
catecholamines and 5-HT to fluorescent condensation products, i.e
formaldehyde-induced fluorescence.
Paraformaldehyde is a solid polymerized form of formaldehyde
(polyoxymethylene).
Under reduced pressure, and more readily with elevated temperature, it gases
off as formaldehyde.
Check 'Histochemistry: theoretical and applied' by the late A.G. Everson
Pearse. The father of histochemistry.


Bryan
----- Original Message -----
From: "Kelly D Mcqueeney" 
To: "Histonet" 
Sent: Friday, February 18, 2005 2:54 PM
Subject: [Histonet] Dry paraformaldehyde vapor


> In order to avoid tritium contamination of screens, I have been fixing
> my slides with paraformaldehyde vapor. PF powder is placed in the bottom
> of a dessicator with slides. Air is removed from the dessicator and the
> air-tight chamber exposes the tissue to paraformaldehyde overnight. Has
> anyone used this method? I am having a hard time understanding why the
> powder alone is sufficient for fixation. Liquid fixative is not an
> option because the receptor/lingand complex is washed off. The protocol
> is vaguely outlined in Biotechiques 26:432-434; Liberatore, et. al. 1999.
>
> Thanks for your input,
> Kelly
>
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