Swing-Out vs. Fixed-Angle Rotors

In a swing-out rotor, the buckets swing out horizontally. This allows for horizontal centrifugation and separation of the sample. As the name implies, a fixed-angle rotor is at a fixed angle (30°- 45°), which causes separation to occur at an angle. In a swing-out rotor, the pelleted material will pellet in the bottom of the tube, while in a fixed-angle rotor, the material will pellet against the side of the tube. This can make it difficult to transfer the supernatant without disturbing the pelleted material. However, fixed-angle rotors can reach much greater speeds, and thus are suitable for applications where top speed is required.

	Fixed-Angle	Swing-Out
Pros	Can reach greater speeds/higher gravitational force Hold more samples Shorten centrifugation time	Pelleted material sediments to the bottom of the tube rather than along the side More formats/applications Interphase barriers are more stable Can create vertical gradient banding
Cons	Pelleted material sediments along the edge of the tube at the angle of the rotor Pelleted material may get caught in the angle of the tube	Cannot reach sufficient speeds for some applications Fits fewer tubes

Sedimentation in a swing-out (left) or fixed-angel (right) rotor

Applications for fixed-angle rotors

The separation of biological macromolecules, such as RNA, DNA and protein, requires greater gravitational force than pelleting animal and plant cells. Isolation of bacterial ribosomes, for example, requires centrifguation at 100,000 x g. Thus fixed-angle rotors are often necessary for efficient sedimentation of these macromolecules. Additionally, because of the reduced time needed for pelleting, any application that requires quick pelleting of a sample would be best suited for a fixed-angle rotor.

The Eppendorf Microtube Rotor (F-45-24-11) fits 24 Eppendorf tubes (1.5-2 mL) and has available adapters to fit 0.2mL PCR tubes, and 0.4mL and 0.5mL microtubes

Applications for swing-out rotors

Because the vessels will spin horizontally, sedimentation will occur at the bottom of the tube or vessel. Thus, this is ideal for any applications that do not require the higher G-force of a fixed-angle rotor, but do require precise separation, such as phase-separation applications (e.g., phenol-chloroform extraction), as interphase barriers are more stable following centrifugation in a swing-out rotor. Another important application is the creation of gradients, which necessitate vertical banding for efficient particle separation. Pelletting of live cells, which requires low speeds in order to maintain cell viability, is another great application for swing-out rotors. Swing-out rotors come in a variety of formats for various tube sizes and shapes, ranging from 0.2 mL PCR tubes to multiple liter buckets, as well as specialized rotors for microplates, which are not available in fixed-angle rotor formats.

Hermle 4 Position Swing Out Rotors and Inserts

Low-Speed Swing Out Microplate Rotor by Hermle

For clinical applications, such as the separation of plasma and serum for clinical chemistry, swing-out rotors are generally desirable. This is because the barrier between plasma and serum components of the blood is more stable. Despite this, small, low-cost fixed-angle centrifuges marketed as “clinical” centrifuges are more common in clinical laboratories, such as the Scilogex SCI506 Low Speed Clinical Centrifuge.

Scilogex SCI506 Low Speed Clinical Centrifuge