Protein stability in acetonitrile - storage conditions? - (Oct/28/2007 )

Hi all,
does anyone have any practical experience with storing protein sample (fractions from reverse phase chromatography) in acetonitrile (20-80%) with 0.06% TFA - how long it can be stored at 4C and -20C and -80C?
I stored my samples one week at -20C and samples with high concentration of acetonitrile were not completely frozen, so I am a little bit worry whether proteins can be partially degraded?

Thanks in advance,
vic

Even if the soluiton is not frozen, I think the proteins in it should still be stable.