Fw: Dialysis speed

Deanne Bell dbell at qnis.net
Fri Mar 16 12:37:08 EST 2001

For this question, the concentration gradient of importance is the water.  

A molecule in a water suspension/solution (7M Urea) will move from the area
of lowest diluent (7M Urea) to highest diluent (pure water) more quickly
than it will move into an area that has less diluent (20X SSC).

This is simple diffusion problem with dialysis membrane blocking molecules
of certain sizes right?  You need to realize that the water molecules will
also be moving across the membrane.  The 20X SSC solution *may* end up
concentrating the Urea on the wrong side of the membrane because the WATER
from the 7M urea solution may diffuse into the 20X SSC.  (I don't know what
20X SSC is so I can't say for sure).

D. Bell

> From: Ole Hartvig Mortensen <ohm at NOSPAMnerd.dk>
> To: methods at hgmp.mrc.ac.uk
> Subject: Re: Dialysis speed
> Date: Friday, March 16, 2001 3:25 AM
> > :Here is the question:
> > :Would the dialysis speed of 7M Urea into pure water be slower than,
> to
> > :or faster than into a 20X SSC solution?
> >
> > OK, I think it is simple. Higher than water viscosity of SSC
> > will make dialysis against SSC slower.
> >
> Dialysis of UREA against something that has a higher salt concentration
> water would
> as far as I know be slower (if the dialysis gradient is dependent on salt
> concentrations of
> other salts besides UREA - this might not be the case, anyone knows ?)


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