Editing Ultracentrifuge (section)

==Instrumentation==
Ultracentrifuges are available with a wide variety of rotors suitable for a great range of experiments.  Most rotors are designed to hold tubes that contain the samples.  ''Swinging bucket rotors'' allow the tubes to hang on hinges so the tubes reorient to the horizontal as the rotor initially accelerate.<ref>{{Cite web|title=Swinging-Bucket Centrifuge Rotors - Beckman Coulter|url=https://www.beckman.com/centrifuges/rotors/swinging-bucket|access-date=2021-10-13|website=www.beckman.com}}</ref>  ''Fixed angle rotors'' are made of a single block of material and hold the tubes in cavities bored at a predetermined angle.  ''Zonal rotors'' are designed to contain a large volume of sample in a single central cavity rather than in tubes.  Some zonal rotors are capable of dynamic loading and unloading of samples while the rotor is spinning at high speed.

Preparative rotors are used in biology for pelleting of fine particulate fractions, such as cellular organelles ([[Mitochondrion|mitochondria]], [[microsome]]s, [[ribosome]]s) and [[virus]]es.  They can also be used for [[gradient]] separations, in which the tubes are filled from top to bottom with an increasing concentration of a dense substance in solution.  [[Sucrose]] gradients are typically used for separation of cellular organelles.  Gradients of [[caesium]] salts are used for separation of nucleic acids.  After the sample has spun at high speed for sufficient time to produce the separation, the rotor is allowed to come to a smooth stop and the gradient is gently pumped out of each tube to isolate the separated components.