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<P><FONT size=2>Fumio,<BR><BR>There is a limit on the maximum gradient that can
be measured (fringes/mm) due to Weiner (? spelling) skewing, and you are
exceeding that limit. As Ariel said you should switch to 3 mm
centerpieces, and then at some point to get to higher concentrations you would
have to drop the rotor speed too to broaden the boundaries. If you look through
the old RASMB postings you will find a number of excellent posts from
others about Weiner skewing and proper optical alignment to minimize distortion
of strong gradients.<BR><BR>But probably the more important question is what are
you going to be able to do with such data even if you collect it? Remember, in
velocity there is hydrodynamic non-ideality as well as thermodynamic
non-ideality, so the non-ideality effects will kill you at much lower
concentrations than in equilibrium. To my knowledge the only model
available to analyze a velocity experiment at 10 mg/mL is a single
non-ideal species. At high concentrations you cannot even correctly measure the
fractions of different components (e.g. aggregates) in a multi-component mixture
due to the Johnston-Ogston effect.</FONT></P>
<P><FONT size=2>John</FONT></P>
<P><FONT size=2>-----Original Message-----<BR>From: rasmb-bounces@rasmb.bbri.org
[</FONT><A href="mailto:rasmb-bounces@rasmb.bbri.org"><FONT
size=2>mailto:rasmb-bounces@rasmb.bbri.org</FONT></A><FONT size=2>] On Behalf Of
Fumio Arisaka<BR>Sent: Saturday, April 05, 2008 4:20 AM<BR>To:
rasmb@server1.bbri.org<BR>Subject: [RASMB] [Fwd: interference
optics]<BR><BR>Dear RASMBers,<BR><BR>This concerns measurement of high
concentrations of IgG with interference optics. I have not much experience with
IF, but have started to use it for the necessity to measure high concentration
samples. Concentrations less than 5 mg/mL had no problem.<BR>Attached jpg file
is to show the problem at 10mg/mL. Somehow, the boudaries tend to go
horizontally before reaching the plateau.<BR><BR>I thought this was due to the
misalignment of optics or something, because the fringe pattern is not so good
as I expect, but the BeckmanCoulter person who came to fix it could not make it
better.<BR><BR>I would like to know what is the common highest concentration
that you could measure by IF. As I understand one could measure SE at higher
concentrations than 100 mg/mL, but when the boundary gets too steep in SV
measurement, the fringes get too much squeezed to count precisely.<BR><BR>Any
comments and advice are highly appreciated.<BR><BR>Best wishes,
Fumio<BR><BR><BR><BR><BR></FONT></P></BODY></HTML>