Types of Rotors in Centrifuge

ROTORS

• Rotor is the rotating unit of Centrifuge.
• Rotor is the movable part of machine which separated the particles present in the sample.
• For low speed centrifugation, rotor is made up of Brass or Steal (low stress) and for high speed centrifugation, rotor is made up of  Aluminium or Titanium (high stress).

DIFFERENT TYPES OF ROTORS

(i) Vertical tube rotors

• Vertical tube rotors are first introduced during 1970’s for high speed and ultracentrifuges.
• The Vertical tube rotor is a fixed zero angle rotor.
• In this, the tubes are aligned vertically in the body of the rotor at all times.
• In Vertical tube rotor, the pellet is deposited along the entire length of the outer wall of the centrifuge tube. It is the major disadvantage because the pellet tends to fall back into the solutions at the end of centrifugation.

(ii) Fixed angle rotors

• Fixed-angle rotors are the most ubiquitous rotors used in centrifugation.
• In Fixed angle rotors, the tubes are placed at a fixed angle between 14° to 40° to the vertical.
• In this rotor, particles migrate to the tube wall before moving towards bottom. Pellets always asymetrically distributed toward the outer aspect of the bottom of the tube.
• The cavities in these rotors range in volume from 0.2 ml to 1 Liter, with speeds ranging from single digits to 10,00,000 × g (relative centrifugal force, RCF).
• Two factors determine the type of Fixed-angle rotor required: desired g - force (RCF) and desired volume.

 (iii) Swinging bucket rotor

• Swinging bucket rotors are ideal for separating large-volume samples (upto 12 Liter) at low speeds.
• It is common in low speed centrifuges.
• Swinging bucket rotor has buckets. During acceleration of the rotor, they swing out from vertical position to a horizontal position.
• They are aligned perpendicular to the axis of rotation and parallel to the applied centrifugal field.
• A swinging-bucket rotor system consists of three parts: 1) the rotor body attaches to the centrifuge drive and has four or six arms to support the buckets, 2) the buckets are placed onto the arms of the rotor body and 3) trunnion pins are used to hold the buckets in place.
• In Swinging bucket rotors, longer distance of travel may allow better separation. So, it is easier to withdraw supernatant without disturbing pellet.

 (iv) Zonal rotors

• There are two types of Zonal rotors namely, (a) Batch type zonal rotor and (b) Continuous flow zonal rotor.

a) Batch type zonal rotor

• The Batch type zonal rotor is extensively used for particle separation when compared to Continuous flow zonal rotor.
• It is designed to increase the sample size.
• Low speed batch rotors are designed to operate near 5000 rpm.
• The high speed rotors are made up of aluminum or titanium and can operate upto 60000 rpm.
• Batch type zonal rotors are used to remove the contaminating proteins from hormones, enzymes, ribosomes, viruses and tissues of plants and animals.      

b) Continuous flow zonal rotor

• Continuous flow zonal rotors are designed for high speed separation of small quantities of solid particles from large volume of liquid suspensions.
• The Continuous flow zonal rotors are similar in shape to the Batch type zonal rotors but differ in the design.
• They are useful for the harvesting of cells and isolating virus in large scale.