Fixed Angle or Swing Out rotor, that is the question!

5/16/2025
A centrifuge is a laboratory instrument that applies centrifugal force to separate components of a mixture based on their density.
 
This process involves spinning a container of fluid or mixture at high speeds, causing denser components to move towards the bottom of the container, where it can be separated from the rest of the mixture and collected for further analysis or use.
To operate, a centrifuge system requires a centrifuge, a rotor, and sometimes buckets and adapters.

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The most commonly used rotor types for benchtop centrifuges are fixed-angle rotors and swing-out rotors, each with unique advantages.
 
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Fixed angle rotor and swing out rotor from OHAUS
 
But which type of rotor do I need?

Fixed-angle rotors are designed to hold samples at a fixed angle while the rotor spins, typically between 30-45°, depending on the rotor.

In contrast, swing-out rotors allow sample buckets to swing outward at varying angles based on the RPM and RCF. During operation, the denser part of the sample is pulled towards the bottom of the tube at an angle defined by the centrifugal force.

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Separation with a fixed angle rotor

In a fixed angle rotor the solids or denser materials (pellet) are pulled to the bottom of the tube at an angle, whereas in swing-out rotors the pellet is sedimented evenly at the bottom of the tube.
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Separation with a Swing out rotor

Therefore, the choice of rotor type depends on the specific application and the materials being separated.
In the following table you can see the main differences between these two rotor types.
 
Differences
Samples is usually at a 'fixed angle' (30-45 degree) Samples are free to swing out at various angles
Sediment at an angle on the bottom of the tube Sediment is evenly at the bottom of the tube
Higher speed centrifugation Lower speed
Short sedimentations times Longer  sedimention times
Smaller capacity Higher capacity (volume of samples and n of tubes)
Because of reorientation loss of material no reorientation during brake
Risk of mixing up the sample  
Differences between a fixed angle rotor and a swing out rotor

In conclusion, fixed angle rotors are often the rotor of choice for separating biological material, such as DNA, RNA and other biological materials, as they require a greater centrifugal force that fixed angle rotors can stand. Higher RCF is also desirable when very compact pellets are required, since the sediment is formed at greater pressure. Furthermore, a higher centrifugal force generally requires less time for centrifugation, which can be crucial for processing large numbers of samples.

On the other hand, swing out rotors offer the best separation location within a container. By allowing sediment to settle at the bottom of the tube, swing out rotors reduce the risk of sediment getting swept back up into the supernatant. This is particularly ideal for separations prior to sensitive analysis, such as LCMS, where solid residue may cause errors, or for applications requiring extremely precise separation.
Swing out rotors are also essential for gradient centrifugation, as they allow the gradient layers to remain in position as the centrifuge stops spinning. They are also necessary for centrifugation of plates.

For more information please contact the OHAUS team