DNA Filtration at New NaCl Concentrations and New Salt Types (LiCl and CsCl)

I ran new experiments over the weekend in which I tested NaCl at 10, 25, 60, and 155mM.  I also ran filtrations in the presence of 10mM LiCl and 10mM CsCl.  These experiments were performed with chips from wafer # 024.  I am only providing the Filtrate / Retentate ratios.  It is obvious that the equilibration time (24 hrs.) was not sufficient for this wafer.  I am currently starting follow up experiments at which equilibrium time is 48 hrs.

[NaCl] (mM)    1/e
10                  6.8
25                 12.8
60                 47.0
155               27.8

NaCl 10mM 1/e = 6.8
LiCl 10mM 1/e = 18.5
CsCl 10mM 1/e = 6.8

This data seems to indicate that a significant change in size exclusion does occur between 10, 25, and 60mM NaCl concentration as illustrated by the change in 1/e value of the exponential decay fit.  It would also appear that LiCl is a more effective shield but that CsCl does not exhibit a significant difference from NaCl.  We believe this may have something to do with the way in which water is ordered around Li ions.

The largest caveat to this data is that equilibration was not reached, making the larger DNA fragments undetectable.  I will be performing follow up experiments with the same membranes but with longer equilibration times (48 hrs).  In addition, I believe there may be a defect in the membrane used to perform filtration at 155mM NaCl.