Saw your post on the Histonet - which PBS are you using? This is
nightmarish.....PFA takes *years* (OK - slight exaggeration) to go into
solution in - for example - Dulbecco's PBS. Are you making up your buffer
from scratch, or buying 10x from Gibco or someone? D-PBS has extra salts
in it which prevent PFA from going into solution - we discovered this the
hard way. Nothing wrong with the commercial PBS, just that this particular
formulation is "bad" for PFA. Which, of course, brings up the question of
which of the million PBS recipes that are out there do you use? We use the
plain old sodium phosphates/sodium chloride mix; Ca/Mg-free.

Anyway - if your PBS is pH'd to above ~6.8 before you dump in the PFA and
start heating, you should be fine. pH 10 is out of control - unless you
are using the fix at that pH.

Tamara Howard
CSHL