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<DIV><SPAN class=796290423-08082006><FONT face=Arial color=#0000ff
size=2>Jack,</FONT></SPAN></DIV>
<DIV><SPAN class=796290423-08082006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=796290423-08082006><FONT face=Arial color=#0000ff size=2>I
agree with Jack Correia that you should try swapping cells to see whether this
variation is really associated with the particular cell or the position in
the rotor. If it is the cell, then also try swapping centerpieces between
housings.</FONT></SPAN></DIV>
<DIV><SPAN class=796290423-08082006><FONT face=Arial color=#0000ff size=2><SPAN
class=796290423-08082006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN></FONT></SPAN> </DIV>
<DIV><SPAN class=796290423-08082006><FONT face=Arial color=#0000ff size=2><SPAN
class=796290423-08082006><FONT face=Arial color=#0000ff size=2>This issue might
be related to convection. First be sure your centerpieces have no scratches or
roughness inside the channels (this often happens when people fill them using
syringe needles). Sometimes too when you have a severe leak at high speed
the center rib gets permanently bowed, which is not always easy to see by
eye.</FONT></SPAN></FONT></SPAN></DIV>
<DIV><SPAN class=796290423-08082006><FONT face=Arial color=#0000ff size=2><SPAN
class=796290423-08082006></SPAN></FONT></SPAN> </DIV>
<DIV><SPAN class=796290423-08082006><FONT face=Arial color=#0000ff size=2>One
other possibility might be that the alignment marks on your rotor or cell
housings are incorrect (although if this is truly a problem that did not
exist 2 years ago that cannot be the cause). I don't know the age of your rotor
but there was definitely a period some years back where the marks on the rotors
were not positioned properly. The cell alignment tool sold by BITC at
U.N.H. would take care of that issue (assuming the slots in the cell housings
are properly located). Similarly, at another time some centerpieces were
produced where the key slot was not properly centered between the
channels.</FONT></SPAN></DIV>
<DIV><SPAN class=796290423-08082006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=796290423-08082006><FONT face=Arial color=#0000ff
size=2>John</FONT></SPAN></DIV>
<DIV><SPAN class=796290423-08082006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=796290423-08082006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN>
<DIV></DIV><FONT face=Tahoma><FONT size=2><FONT face=Arial><FONT
color=#0000ff><SPAN
class=796290423-08082006> </SPAN></FONT></FONT>-----Original
Message-----<BR><B>From:</B> rasmb-bounces@rasmb.bbri.org
[mailto:rasmb-bounces@rasmb.bbri.org] <B>On Behalf Of </B>jack
kornblatt<BR><B>Sent:</B> Tuesday, August 08, 2006 2:08 PM<BR><B>To:</B>
rasmb@server1.bbri.org<BR><B>Subject:</B> [RASMB] s values as function of cell
position<BR><BR></FONT></FONT></DIV>
<BLOCKQUOTE dir=ltr style="MARGIN-RIGHT: 0px">
<DIV><FONT face=Arial size=4>I have recently come across a problem the
answer to which I cannot find in the Archives.</FONT></DIV>
<DIV><FONT face=Arial size=4>The problem is this: If I run the same sample in
the AUC at the same temperature and speed over the course of 5 days, I get a
distribution of s values that has a spread of plus or minus <0.4%. The
sample is quite stable and shows no suggestion of degradation between days 1
and 4 but a small peak (< 2% of the total) shows up on day 5. The
perplexing thing is that there are systematic differences between cells
1, 2 and 3. The s values in cell 1 are always highest, the s values in cell 2
are lowest and the s values in cell 3 intermediate. The differences are small.
Cell 1 s values are about 0.4% less than those of cell 1. </FONT></DIV>
<DIV><FONT face=Arial size=4>The samples in the three cells are the same; they
were taken from the same batch. The buffer is the same. </FONT></DIV>
<DIV><FONT face=Arial size=4>The problem has only become evident recently. It
was not present two years ago but I cannot state unequivocally when it first
started to occur.</FONT></DIV>
<DIV><FONT face=Arial size=4>Has anyone suggestions as to cause and what might
be done to correct the problem?</FONT></DIV>
<DIV><FONT face=Arial size=4></FONT> </DIV>
<DIV><FONT face=Arial size=4>thanks for any help you can give</FONT></DIV>
<DIV><FONT face=Arial size=4>jack
(kornblatt)</FONT></DIV></BLOCKQUOTE></BODY></HTML>