Paraformaldehyde shelf-life?

[Francisco Javier H Blazquez]

In article 656 at mnemosyne.cs.edu, anon1167 at nyx.cs.du.edu (M) wrote:

>
>I was recently told that, when using paraformaldehyde for
>perfusion, the P must be made immediately prior to perfusion. 


	
In fact, when the paraformaldehyde powder is heated to 60 oC, a gas is
liberated from the polymerizated form. This gas is the formaldehyde which
dissolves in the hot water. Without the methanol as a stabilizer, the gas is
lost and the concentration drops.
	We usually dissolve the paraformaldehyde in the alkaline form of the
	Sorensen's phosphate buffer and this solutions is stored as a 20% stock 
	solution at 37% to prevent precipitation.
	     Small aliquots can then be taken and dissolved to a 4% solution in 
	the acid form of the phosphate buffer.
	      Some references about this subject may be mailed.
	
	
	Francisco J. Hernandez-Blazquez.....Department of Histology
	                                    Instituto de Ciencias Biomedicas
	                                    Universidade de Sao Paulo
	                                    Av. Prof. Lineu prestes, 1524
	                                    05508-900 - Sao Paulo (Brazil)
	INTERNET..........................fjhblazq at fox.cce.usp.br