4% PFA is a very good fixative. The difference between 4% and 10% is 
that the PFA is made fresh each time and has no impurities added ex: 
methanols. The formalin content in both comes out to about the same. It 
is a standard fixative for many research labs. You can drop fix with PFA 
or perfuse and then drop fix for additional time for very good fixation 
and excellent results. I have used it for my mouse brain tissue for over 
6 years with very nice results.

Colleen Forster
U of Mn


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