[RASMB] Protocol for Gravitational Sweep Sedimentation Velocity Study

[Falabella, James]

Dear RASMB Members,

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.

Thank you in advance for your advice,

James Falabella
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