15% Picric acid + 2% Paraformaldehide fix

If you don't remember how to prepare and dilute solution go here

Preparation:

1) Carefully heat up 15ml double filtered saturated picric acid to 60oC
2) Add 2g paraformaldehide (It will get all thick and cloudy)
3) Slowly add strong NaOH (5N) until everything is in solution.  "Clear" is when you can't see any more particles in the picric acid.  The original recipe calls for 2.52% NaOH but it does not have to be exacly 2.52%
4) Filter again and fill to 100ml with phosphate buffer and keep at 4oC in a dark bottle
5) Make sure pH is ~7.3

This fixative solution stays good almost for ever in the fridge (4oC) if kept in a dark bottle. It's ready for use. The osmolarity is ~900mOsm and good for marine animals.

Note

1) ALWAYS put the date on a freshly made solution.Also add your initials, pH and concentration

2) Label anything that touches fixative solution with the words FIX (or something like that).  Dishes or stirrers once used for fix should not be used to make non-fix solutions!!!

Copyright: STG Lab 2006
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Last Modified:March 06, 2009