There has been a lot of discusion re formalin versus paraformaldehyde ad concentrations.
In most cases it will not make a lot of difference whether PFA or formlin are used.
I am concerned that in the rush to use paraformaldehyde instead of formalin because of purity concerns  may result in more accidents when heating the solution to make the paraformaldehyde go into solution.
If you are concerned with the purity of formalin then purchase the closed vials of formalin that are available from several manufacturers and that can be stored for a reasonable long time.
First however I would run tests to determine whether  the formalin that you are using is really unsuitable. Standardization is important.
Similarly I believe that the concern for a ensuring that frormalin used be within very narrow concentration limits is also somewhat of an overreaction. The fixation process relies on availability of formalin and time of fixation etc.  Concentration within  few percentage points is not that important.
Barry

________________________________

From: histonet-bounces@lists.utsouthwestern.edu on behalf of K.R. Vinod
Sent: Wed 8/9/2006 10:54 PM
To: histonet@lists.utsouthwestern.edu
Subject: [Histonet] PFA v. formalin



 Hello Melissa

Usually, tissues are fixed in 4% PFA (Paraformaldehyde) for 3 to 4 hours at
4 °C.  10% formalin in PBS can also be used.
Tissues fixed for long time in formalin may not give good result. However,
it depends on what type of tissue you are using.

K.R. Vinod, Ph.D.
Glenmark Research Centre, New Bombay.
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