pmsf not dissolving in buffer - (Feb/17/2008 )

hi all
i often use pmsf in ips e.tc
It dissolves in stock solutions.
I have a problem
I have tried many times but pmsf does not seem to dissolve in buffers
as soon as i add ; it forms 'flake' like structures that float on the surface and which
break into smaller sized particles upon pipeting.
if i see my buffer by keeping it near a ligh sourse i can see these particles floating and scattering light
they dont go no matter how long i pipete.
i use 1-2mM conc of pmsf.

i have tried making stock in isopropanol and in methanl as well
but the problem persists

What I usually do is, dissolve 100mM PMSF in isopropanol and store under -20°C. When I have to add them into solution, I will briefly warm them at 37°C since usually PMSF is precipitated under low temperature. Then I add the "dissolved" PMSF into solution.

That's what I do too, except for the part at -20 C. 100mM in isopropanol works well for me.

you could make PMSF stock solution in 100% ethanol.