[RASMB] Boundary convection problem in the Optima ultracentrifuge

[Laue, Thomas]

Hi-
Good to know. On the Optima, the problem will appear during a heating cycle. I believe the Optima does not use PID (proportional) thermal control, so the heating pulses can be large enough and long enough to not dissipate sufficiently before reaching the cells.
In the XLI, the expectation is the opposite. Since the TE modules are towards the center of the rotor, a destabilizing thermal gradient can be produced during the cooling cycle.
In both cases, allowing a long enough equilibration time minimizes (but does not eliminate) the potential for convection.
Best wishes,
Tom

From: RASMB <rasmb-bounces at list.rasmb.org> On Behalf Of Walter, Johannes
Sent: Wednesday, March 10, 2021 4:17 AM
To: rasmb at rasmb.org
Subject: Re: [RASMB] Boundary convection problem in the Optima ultracentrifuge

Caution - External Email

Dear Tom,

Thank you very much for that very interesting paper. Fortunately, we do not observe any convection issues with our Optima as long as the temperature equilibration is at least 6 h (below that, we see severe issues for many analytes). By the way, there is a very interesting study by Sloutskin et al.:
https://www.sciencedirect.com/science/article/pii/S0927775715003180<https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.sciencedirect.com%2Fscience%2Farticle%2Fpii%2FS0927775715003180&data=04%7C01%7Ctom.laue%40unh.edu%7C93dc6a5704344ae4039708d8e3a57776%7Cd6241893512d46dc8d2bbe47e25f5666%7C0%7C0%7C637509647557566997%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=t6Wm%2F9ayKAMipjL1faJaAK%2F4ryYDdWf7aNMRmFyHenw%3D&reserved=0>
They studied convection and layering effects in analytical centrifugation, where similar issues are observed due to the cooling system.

Best wishes,
Johannes

Von: RASMB <rasmb-bounces at list.rasmb.org<mailto:rasmb-bounces at list.rasmb.org>> Im Auftrag von Laue, Thomas
Gesendet: Dienstag, 9. März 2021 21:41
An: RASMB <rasmb at rasmb.org<mailto:rasmb at rasmb.org>>
Betreff: [RASMB] Boundary convection problem in the Optima ultracentrifuge

Dear all-
Data acquired using the Optima ultracentrifuge may exhibit boundary convection, thus confounding the precision and accuracy of data analysis and interpretation from this instrument. Not all instruments exhibit the phenomenon, and the problem is intermittent on others. The root cause are thermal 'waves' that travel from the rotor edge towards the center. These waves produce density gradients in the solution which, in turn, may be driven by the gravitational field to cause turbulent flow and consequent mixing between adjacent sample regions. The problem is most pronounced in low-concentration buffers where little-to-no stabilizing density gradient forms due to solvent component redistribution.
There is a paper available describing the problem, its causes, how to detect it and ways to minimize its occurrence: https://biorxiv.org/cgi/content/short/2021.03.08.434487v1<https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbiorxiv.org%2Fcgi%2Fcontent%2Fshort%2F2021.03.08.434487v1&data=04%7C01%7Ctom.laue%40unh.edu%7C93dc6a5704344ae4039708d8e3a57776%7Cd6241893512d46dc8d2bbe47e25f5666%7C0%7C0%7C637509647557576957%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=20rLmmSF2IZFA2tLrXBFOiUxhWQQwu4jE0G9Bw6YdIs%3D&reserved=0>
Best wishes,
Tom


Professor Emeritus
University of New Hampshire

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