ultracentrifuges

An ultracentrifuge is a high-speed centrifuge capable of generating centrifugal forces greatly exceeding those of standard laboratory centrifuges. Most operate at speeds above 100,000 g, corresponding to rotor speeds of tens of thousands of revolutions per minute. The force is described as relative centrifugal force (RCF) and depends on rotor radius; RCF ≈ 1.118×10^-5 × r × (rpm)^2, where r is the radius in centimeters.

For operation, samples are placed in small tubes inside a vacuum chamber to reduce air drag, and many models provide refrigerated cooling to maintain sample stability. Common rotor types are fixed-angle and swinging-bucket rotors, made from materials such as aluminum or titanium.

Applications include differential centrifugation to separate cell components, and density gradient centrifugation using sucrose, cesium chloride, or iodixanol to separate particles by density. Ultracentrifugation is essential in purifying nucleic acids, proteins, lipids, viruses, organelles, and macromolecular complexes. Analytical ultracentrifuges are used to study sedimentation properties and molecular weights, while preparative ultracentrifuges isolate materials for further experiments.

Safety and maintenance focus on rotor integrity, balanced loads, and regular inspection. High speeds generate heat, vibration, and risk of rotor failure; operation requires trained personnel and adherence to manufacturer specifications. The technology originated in the early 20th century with advances by Theodor Svedberg and later by industrial firms specializing in high-speed rotors.