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can I re-freeze the 4% paraformaldehyde for longer storage? - leave cells in 4% paraformaldehyde 4 FACS? (Aug/28/2005 )

Hi, everyone:

Regarding to the fixative 4% paraformaldehyde for FACS analysis, I have two questions:

1. Some said that after i made 4% paraformaldehyde, aliquot them into small volumes, then i can store them into -20 degree C. before use, thaw a certain amount of 4% paraformaldehyde and after use put them into 4 degree C and it can be usable in 5 days. My question is after thawed, can I re-freeze them into
-20 degree C freezer for longer storage?

2. after i incubate the cells into 4% paraformaldehyde, can I directly leave the cells in 4% paraformaldehyde overnight or longer until i run the cells onto the FACS machine?

Thanks for any comments and advices!


I leave my cells in 1% PFA in PBS for flow cytometry and run my samples up to 1 week later. You should know that you do get shrinkage of cells from fixation but as long as you adjust your voltages you should be fine.


I also make a batch of 4% paraformaldehyde which is aliquoted and stored in the minus20 (my last batch has already been there a year and still using it). I usually thaw an aliquot at 4degreesC and discard what I don't use within a week.



Hi, guys, thanks for the information! Very helpful!