Fresh 4% PFA for perfusions, or purchased 4% PFA?


Going to try and use affymetrix 4% PFA (in PBS) instead of preparing fresh 4% PFA for fixation. Any thoughts on whether or not this is a bad idea?


It should be fine. My understanding is that the concern with purchased PFA or formalin is that methanol is frequently added as a stabilizer. In rare cases, this may quench endogenous florescence or otherwise mess with your tissue. However, according to the description on Affymetrix website there is no methanol in this preparation so this issue wouldn’t apply. In a pinch I’ve diluted purchased formalin in PBS for fixation and it’s been fine, although my typical approach is to prepare fresh 4% PFA in large batches which I freeze in aliquots to defrost as needed.


@ShanTan I agree with @liz . Should be fine. People use Formalin all the time and it seems to get the job done.
However, regarding PFA… If the reason you don’t want to make it fresh is because it’s a pain, here are some tips.

  1. Use Granular PFA ( This is very easy to weigh out. Very little mess since it’s not powder. Less chance of it fluffing up all over.
  2. Add 1x PBS to 1 L on a hot plate in the hood. Set the heat to 60ºC and put a stir bar in. Cover with foil. Let it mix and heat until it’s fully dissolved. Usually about 1h. No need to use NaOH or pH or anything. It’s a little slower, but easy and requires little manipulation.
  3. Filter through a filter bottle with vacuum after it cools.
  4. Keep for 1-2 weeks at 4ºC (people have different feelings about this, but I haven’t noticed much difference).

I used to hate making PFA because of the pH-ing and the mess.

Good luck.