Vaccuum dialysis?

Dr E. Buxbaum EB15 at
Thu Jul 30 13:19:39 EST 1998

Ian McFarlane wrote:
> Once upon a time somebody mentioned that there was some trick with
> dialysis tubing and vaccuum that could be performed to concentrate
> proteins (flash dialysis?). Does anyone know how to do this or is my
> memory failing me?

You will recall the classical school experiment of Pfeffer's cell, were
water flows across a semipermeable membrane into a solution of higher
solute concentration, until there is an equilibrium between the osmotic
pressure difference between the two solutions and the difference in
hydrostatic pressure. Changing the hydrostatic pressure on either side
of the membrane will change the equilibrium, an effect used to desalt
water (reversed osmosis).

Applying vacuum to the dialysis buffer, with the dialysis bag open to
atmospheric pressure uses the same effect. It is a bit fiddely to set up
such an experiment, and without specialised equipment it may be easier
to add polyethyleneglycol (MW 8000) to the dialysis buffer. If no change
in ionic composition of the dialysate is required, you can simply
sprincle the dialysis bag with PEG8000 powder. But watch the sample
carefully, that it does not dry out completely. 

For larger amounts of sample or regular use a stirred pressurised cell
(Amicon) is more convenient, however.

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