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<p class=MsoNormal><font size=2 face="Times New Roman"><span style='font-size:
11.0pt'>Dear RASMB Members,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Times New Roman"><span style='font-size:
11.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Times New Roman"><span style='font-size:
11.0pt'>I am performing sedimentation velocity to examine the particle size
distribution of 10 nm diameter gold particles that I have intentionally induced
into stable aggregates. I suspect that the aggregates population ranges from
dimers to tetramers. At first, I tried to sediment the aggregated particles at
7000 RPM in an XL-A outfitted with: 4-hole ANTI60 rotor, 12 mm charcoal-Epon
cells, quartz windows and the absorbance scans at 520 nm (with the 400 nm
filter in the light path) appeared mal-formed while the scans of another cell
with the non aggregated 10 nm diameter gold particles are well formed sigmoids
and easily fit by Sedfit. I looked up some references from the literature on the
analysis of wide distribution samples with an analytical ultracentrifuge that
were very good background, however, they did not have a protocol that spelled
out what buttons to press to get the XL-A to collect the data at different
angular velocities. I went ahead with my centrifugation study by performing
several back to back runs where I simply started run after run using the
Beckman software to increase the rotor speed from 3000 to 5000 to 8000 RPM,
however, the 5000 and 8000 RPM runs could not be fit by Sedfit due to the fact
that there was not a long enough acceleration phase from one speed to the next.
I looked through Sedfit and could not find a way to get around this error
and it is probably not a good idea to try my own fix before asking around for
any tips on how to address the proper operation of the XL-A for a gravitational
sweep and data analysis.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Times New Roman"><span style='font-size:
11.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Times New Roman"><span style='font-size:
11.0pt'>Thank you in advance for your advice,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Times New Roman"><span style='font-size:
11.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Times New Roman"><span style='font-size:
11.0pt'>James Falabella <o:p></o:p></span></font></p>
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