Here is the summary I promised and MANY THANKS to all who responded. I
think that you have solved my problems.
Tony Sanchez (tsanchez at eye1.eye.ufl.edu) suggests:
Use of collodian bag with an accelerator -- cumbersome but gives good
Laura K. Moen (LKM100F at oduvm.cc.odu.edu) suggests:
Dialysis against Ficoll or PEG (some may get into sample) If this is
unacceptable dialyze against Sephadex
Use of pressurized cells like Amicon units
Use of centricons -- performance is variable
Bind sample to small volume of strong ion-exchanger and elute with small
Note: success fo concentration depends on protein, buffer & final volume
and concentration one desires
John Kuszewski (johnk at spasm.niddk.nih.gov) suggests:
Use of micro-concentration/dialysis machine from Spectrum. It dialyzes up
to 200 mL against 5L buffer while concentrating to O.5 mL -- "works like a
charm" but filters are not resistant to GdnHCl.