From: Henryk Eisenberg <BPEISENB@WEIZMANN.WEIZMANN.AC.IL>
  To  : RASMB Group <rasmb@bbri.org>
  Date: Thu, 06 May 99 10:18:57 +0300

Partial volume

Dear Carlos:
The problem you raise has recently come up a number of times.
It is an old problem solved long time ago, however it seems that
many of the current generation aficiniados are not aware of it.
When doing equilibrium sedimentation in a mixed multicomponent
system you cannot used a calculated partial specific volume or
one determined in aqueous solution. You must use a density increment
dro/dc determined at dialysis equilibrium, which replaces the
classical Archimedes term (1-vbar.rho) applicable to two component
systems (cf Eisenberg, Bioph.Chem. 53, 1994, 57-68 for further
references). You do not have to repeat the density increment
measurement every time you use a similar solvent. You calculate an
apparent volume psibar from (drho/dc=1-psibar.rho) and all you have
to know now is your solvent density in each experiment.
I hope this will be helpful, Heini