Centrifugal filtration - Picking the right filter size! (Jan/20/2006 )

Hi guys,
I'm hoping to filter and concentrate my protein mixture using centrafugal filters. I'm not 100% how to calculate my filter size, I've been told that the MWCO given for filters isn't an effective guide of what size molecules it will filter.

My proteins of interest lie in the 50-100KD band, I need to remove and discard the proteins over 100KD and those below 50KD so I will require two seperate filters, I'll also need to recover my protein of interest from the filter membrane. Has anyone any advice as to the approximate filter sizes and types I should use.

Many Thanks
Rosie

two centricon columns are ok for your purpose.
Cut off are 100 for YM100 and 50 for YM50 columns