4% Paraformaldehide solution

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

Preparation:

- Prepare 4 volumes of 0.1 M sodium phosphate dibasic (Na₂HPO₄), i.e. 800ml for 1 lt solution
- Prepare 1 volume of 0.1 M sodium phosphate monobasic (NaH₂PO₄), i.e. 200 ml
- Warm the dibasic phosphate solution to 60ºC
- Weigh the paraformaldehide (i.e. 40g for a 1 lt solution, 4g for a 100 ml solution)
- Add to the warm dibasic phosphate stirring constantly (do not exceed 70ºC; if you do, then start again)
- When paraformaldehide has disolved (should take ~ 5min) add the monobasic phosphate solution
- The pH should be about right, but check it. If not correct, then add NaOH or HCl to 7.4
- If the solution has been heated for too long white flakes may appear floating. If too many, start again. If only a few, filter the     solution. Filter also if too dirty.
- Add 400mM sucrose (this is to adjust the osmolarity of the solution to something close to the saline's)

Troubleshooting:

1) Paraformaldehide (the powder) reacts readily with oxigen and oxidizes to a less active form. Thus, in order to preserve it in      the best possible condition it should be weighed in aliquots (2 or 4 grams, for example), packed tightly to eliminate as much air      as possible (ideally in a N₂ atmosphere), sealed in small container and stored frozen.

2) Paraformaldehide solutions go bad rapidly.  Thus, ALWAYS put the date on a freshly made solution, and throw the solution         away after 1-2 days.

3) 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