[RASMB] s20w calculation

[John Philo]

John, unfortunately I think David is correct that SEDNTERP 2 has some bugs.
I didn't reproduce your results, but in my case after entering the correct
vbar, density and viscosity it is always returning identical values for s*
and s(20,w). That is, it seems to be paying no attention to the new values I
entered on the solvent and sample page and still using the default water
values. I suspect this is an order of entry problem.
 
Using SEDNTERP 1.09 and entering your values I get that s* = 16.39
corresponds to s(20,w) = 17.397. FYI if you are running Windows 7 you can
run SEDNTERP 1.09 under the Windows XP virtual machine.
 
John
 
  _____  

From: rasmb-bounces at list.rasmb.org [mailto:rasmb-bounces at list.rasmb.org] On
Behalf Of John Sumida
Sent: Friday, August 09, 2013 10:44 AM
To: drdavidbhayes at yahoo.com
Cc: rasmb at rasmb.org
Subject: Re: [RASMB] s20w calculation



Hi David,

 

Thanks for taking the time to respond. I'm attempting to respond to your
post. Apologies if I'm committing some type of etiquette violation in
responding to the group, but as you requested some clarification as to my
process I thought to respond publicly.

 

To answer your questions.

 

I've been trying to understand why this particular polymer material produces
a large s20w value when another material with different surface charge
properties produces an s20w of 7.9s and sediments very differently.

 

So the back calculation, going from s20w to s*, was me playing with the data
to see if I could go from the 17.3 s20w back to s* which I would have hoped
- as you point out - would not have been much different from 17.3s.

 

My initial calculation using the s20w correction equation  (equation 19) was
comforting in that the calculated s* was 16.4s.  I used SEDFIT to perform
the same calculation just to check that all was in order - and as I stated
SEDFIT returned the 16.4s value as had the calculation and the analysis in
SEDANAL.  Note that vbar and solvent parameters had been entered in into the
experiment file and gOfs files had been generated by running DCDT.  So I
believe the s values returned in SEDNAL are s20w values.

 

The problem arose when I used the Experiment page in SEDNTERP (version
20120828 BETA). Using the calculated value of s*, SEDNTERP did not return
the same value for s20w that SEDANAL output. 

 

I also attempted the same operation using the web version of SEDNTERP which
resulted in the same result, namely calculating an s20w of 27.8s when the
experimentally observed s20w was17.3s.

 

I had not thought to turn off the s20w calculation (in order to do so do I
just remove vbar from the experiment info?) and attempt to fit for s*.  Will
try that next.

 

Best regards,

 

John Sumida, Ph.D.

 <http://depts.washington.edu/cidb4bio/index.shtml> Analytical Biopharmacy
Core Facility

University of Washington

 <http://www.moles.washington.edu/> Molecular Engineering & Sciences
Institute, G22

3946 West Stevens Way NE

Seattle WA 98195-1653

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