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From:"R.Wadley" <>
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	Dear John,

	I'm not a chemist, but the answer is they are exactly the same (except one
is obviously buffered) with respect to their formaldehyde content.
However, commercial formaldehyde does contain methanol, where prepared
paraformaldehyde does not (unless you add it in when you make it).

	In the beginning:

	Formaldehyde is a gas, it is purchased as a saturated solution (gas in
water) of 40% formaldehyde gas per volume of water.  10 - 15% methanol is
added to limit the degree of polymeristation of the formaldehyde molecules.
 The formaldehyde molecule is a short chain that likes to link up with lots
& lots of its mates.  Methanol limits this.  Short chains of formaldehyde
fix tissue much better than really long ones.

	If you leave your bulk 40% formaldehyde in the back of the cupboard for
long enough it polymerises & you get all this white precipitate in the
bottom.  The white stuff is paraformaldehyde.

	Dissolving paraformaldehyde in a slightly basic warm solution of water
gives you formaldehyde at the concentration you wanted (if you followed the
method right!).

	Therefore, 10% NBF is equal to 4% paraformaldehyde, because you dilute
your 40% stock commercial formaldehyde 1:10 to get 10% NBF (if you use a
buffer) or 10% formalin if you don't use buffer.  

	Hopefully more clearly 10% of 40% = 4%.

	Hope thats clearer than mud.

	I'd be happy to help with any further questions you may have.


	Rob W.


At 11:55 02/15/2000 -0500, you wrote:
>I thought there was little or no difference between 4% paraformaldehyde and
>10% neutral buffered formalin.  Will a chemist step in and resolve my
>>Date: 11 Feb 2000 05:34:11 -0600
>>From: "Shelton, John" <>
>>Subject: FLT-1/FLK-1 ISH
>>Some suggestions:
>>#225# Paraformaldehyde instead of formalin
>>John Shelton
>>Research Scientist
>>UT Southwestern

R. Wadley, B.App.Sc. M.L.S, Grad.Dip.Sc.MM
Laboratory Manager
Cellular Analysis Facility
School of Microbiology & Immunology
UNSW, New South Wales, Australia, 2052
Ph (BH) 	+61 (2) 9385 3517
Ph (AH)	+61 (2) 9555 1239
Fax 	+61 (2) 9385 1591

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