My SLC NSH convention workshop recommended

NBF, 10% aq
4% paraformaldehyde
10% NBF
formal saline

ZN formalin works for ISH.

Fix fresh tissues 8 hours to 3 days.
Rationale:  Cross linking fixatives keep DNA in place

Avoid:  Bouins, 2% gluteraldehyde, Zenker, B-5, acetone/alcohol,
Rationale:  any heavy metal or picric acid destroys DNA., Glut is a
crosslinker,
but the PCR reagents cannot penetrate.

Great workshop by two gals who REALLY knew their RT-PCR!

Gayle Callis