Solute separation by centrifuge

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Discussion Overview

The discussion centers on the feasibility of separating solutes from solvents using centrifugation, including the potential for molecular disassociation at extreme rotational speeds. Participants explore various scenarios, including the separation of isotopes and the behavior of solutions under centrifugation.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • Some participants propose that it is possible to separate any solute from any solvent by centrifuge, including heavy water from H1 water.
  • Others argue that certain solvents and solutes cannot be separated by centrifuge, citing examples like different variants of hydrocarbons with the same density.
  • There is a suggestion that molecular disassociation could occur at high RPMs, particularly for long-chain molecules under rotational forces.
  • One participant mentions that centrifugation can be used to separate isotopes, specifically how enriched uranium is obtained for reactor fuel and bombs.
  • Questions are raised about the behavior of saturated or supersaturated solutions in a centrifuge, including the potential for crystallization and the development of concentration gradients.
  • Some participants discuss the application of centrifugation in molecular biology, referencing the separation of DNA isotopes to demonstrate semi-conservative replication.
  • There is a distinction made between the gaseous and liquid phases in terms of uranium isotope separation, with some claiming that the phase affects the degree of separation.

Areas of Agreement / Disagreement

Participants express multiple competing views on the ability to separate solutes from solvents using centrifugation, with no consensus reached on the feasibility of such separations in all cases.

Contextual Notes

Limitations include the dependence on specific densities of solutes and solvents, the effects of rotational speed, and the potential for molecular disassociation under extreme conditions. The discussion also highlights the complexity of separation processes, particularly in biological contexts.

neanderthalphysics
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If energy (in)efficiency was not a factor, is it possible to separate any solute from any solvent by centrifuge? At extreme RPMs, is molecular disassociation possible?
My view is that it is possible to separate any solute from any solvent by centrifuge. Likewise it is possible to separate heavy water from H1 water by centrifuge.

Molecular disassociation is probably a borderline possibility, especially if we consider the molecular disassociation of your centrifuge by too high RPMs! But maybe, if you have a long chain molecule with two heavy atoms on the ends, and it is forced to bend under the rotational forces, then it might break the bonds.
 
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neanderthalphysics said:
Summary:: If energy (in)efficiency was not a factor, is it possible to separate any solute from any solvent by centrifuge? At extreme RPMs, is molecular disassociation possible?

My view is that it is possible to separate any solute from any solvent by centrifuge. Likewise it is possible to separate heavy water from H1 water by centrifuge.

Molecular disassociation is probably a borderline possibility, especially if we consider the molecular disassociation of your centrifuge by too high RPMs! But maybe, if you have a long chain molecule with two heavy atoms on the ends, and it is forced to bend under the rotational forces, then it might break the bonds.
No. You can find solvents and solute which are not separable by centrifuge. For example, different variants of hydrocarbons with same density.
Also, the centrifuge itself will break long before any gravity-chemical effects would be noticeable.
 
trurle said:
No. You can find solvents and solute which are not separable by centrifuge. For example, different variants of hydrocarbons with same density.
Also, the centrifuge itself will break long before any gravity-chemical effects would be noticeable.

Thanks for your inputs.

Can you give some examples of solvents and solute which are not separable by centrifuge?

If we go for something basic (excuse the pun) like KOH in water where the former is highly soluble in the latter, will you get an increasing concentration gradient as you spin the centrifuge faster?

What happens if you have a saturated or even supersaturated solute in a solvent, and then you spin it in a centrifuge? Will you start getting crystallization?

Tom.G said:
It can however be used to separate various isotopes of elements. For instance that is how enriched Uranium is obtained for reactor fuel, and for bombs.

https://science.howstuffworks.com/uranium-centrifuge.htm

I guess with a stretch of imagination one could view the U-235 and U-238 isotopes in a uranium centrifuge as a "solvent" and "solute" both of which are infinitely miscible with the other with interchangeable definitions of solvent and solute.
 
neanderthalphysics said:
Thanks for your inputs.

Can you give some examples of solvents and solute which are not separable by centrifuge?

If we go for something basic (excuse the pun) like KOH in water where the former is highly soluble in the latter, will you get an increasing concentration gradient as you spin the centrifuge faster?

What happens if you have a saturated or even supersaturated solute in a solvent, and then you spin it in a centrifuge? Will you start getting crystallization?
I guess with a stretch of imagination one could view the U-235 and U-238 isotopes in a uranium centrifuge as a "solvent" and "solute" both of which are infinitely miscible with the other with interchangeable definitions of solvent and solute.
For example, phenol and water. Densities are very similar.
Saturated solution under centrifuge may become super-saturated if difference in density is large enough.
You need rotational speed about ~100 (m/s)/(g/cm3)
 
The Uranium isotope separation mentioned earlier is one example. Of course you don't get some drastic all-or-none separation, your get quantitative enrichment, and a cascade of processes is needed (fortunately).

The principle has a classical application in molecular biology which is in all the textbooks. Centrifuge a solution containing a heavy ion fast enough, long enough you will get an equilibrum density gradient which is just the same principle as the gradient of air density of the atmosphere. Will be a shallow gradient but that is okay for the application, which is to separate macromolecules of closely similar density.

The question was when the (double-stranded) DNA molecule replicates in cellular duplication, how does the original DNA distribute between daughter cells? It was known that the original DNA was not destroyed - DNA is radioactively labelled (e.g. by growing bacteria in radioactive thymidine) all the DNA radioactivity is still found in the DNA of the daughter cells. But what way was it distributed? I.e. if we represent an existing strand as | and a newly produced strand as | , so the original DNA is || , when the cell has duplicated are progeny || and || (called 'conservative replication') or are they || and || (called 'semi conservative replication')? (They are not || and || (nonconservative) from what was mentioned above, the parent DNA strands are conserved.)

Cells were grown in a medium where their nitrogen source was the (nonradioactive) nitrogen isotope 15N. This gives a DNA slightly more dense than that with the normal 14N isotope. So || , || and || have three different densities and will eqiilibrate settling at different heights in the centrifuge tube in which a gradient of CsCl is established, and in this way it was possible to verify that replication produced || i.e. is semiconservative.

See any textbook or look up 'semiconservative replication' or 'Meselson & Stahl experiment'.
 
Last edited:
Tom.G said:
It can however be used to separate various isotopes of elements. For instance that is how enriched Uranium is obtained for reactor fuel, and for bombs.

In gaseous phase, not in solution.
 
Surely whether it is in the gaseous or liquid phase just affects separation by a matter of degree?
 
neanderthalphysics said:
Surely whether it is in the gaseous or liquid phase just affects separation by a matter of degree?
Yes.
gaseous phase U235:U238 separation: known (I believe as their hexafluorides)

Liquid phase U235:238 separation: unknown
 

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