The word centrifuge comes from the Latin word centrum which means centre and fugere which means to escape. The centrifuge is made to separate a mixture’s constituent components using the centrifugal force produced by circular movements. Numerous centrifuges are available to meet particular industrial and research requirements. The standing centrifuges that are typically seen in clinical and public health labs are the subject of this chapter.

Purpose of Centrifuge

The centrifuge uses centrifugal force, which is the force produced when an object rotates around a single point, to separate solids suspended in a liquid by sedimentation or liquids of different densities. The rotational movements allow for the generation of forces much greater than gravity in controlled periods of time.

In the laboratory, centrifuges are typically used for processes like the sedimentation of solid components from biological liquids, particularly blood components, such as red blood cells, white blood cells, and platelets, among others, as well as for conducting multiple tests and treatments. There are several types of centrifuges; the most popular types in clinical, public health, and surveillance labs are the tabletop centrifuge, the ultracentrifuge, the hematocrit centrifuge, and the standing centrifuge.

Centrifuge: Parts, Types, Operation and Maintenance

Operation Principles

Newton’s law of motion is put into practice via centrifuges. A centripetal force [N] with magnitude N = mω2R, where [m] is the body’s mass, [R] is its radius, and ω is its rotational speed, is applied to the rotation axis when a body of mass [m] rotates around a central point [O]. Centrifuges have a rotor with sample-receiving compartments positioned on a spinning axis. The following formula defines tangential speed: VT=ωR.

The samples are exposed to the same magnitude of centrifugal force Fp, but in the opposite direction, when the system spins at ω radians per second. A diagram of the idea, its real-world application, and the outcome is displayed in the picture below 1. Due to differences in density, the particles in the substance being centrifuged separate as a result of this Fp force acting on them.
Lighter particles take longer to settle upon those of higher density, while denser particles will settle at the tube’s bottom in shorter amounts of time. The relative centrifugal field, or [RCF], is the relationship between the centrifugal acceleration [ω2r] to a given radius [r] and the force of gravity [g]. When comparable centrifugal effects are needed, the RCF is the instrument that makes it possible to compare rotors with various specific cations.

RCF = rω2 /g

Components of centrifuge

The most important components of a centrifuge are:
The electric/electronic control which generally has the following elements:

1. On and off control, operation time control (timer), rotation speed control (in some centrifuges), temperature control (in refrigerated centrifuges), vibration control (safety mechanism) and brake system.
2. Refrigeration system (in refrigerated centrifuges).
3. Vacuum system (in ultracentrifuges).
4. Base
5. Lid/cover
6. Casing
7. Electric motor
8. Rotor. There are different types of rotors. The most common are the fixed angle, the swinging buckets, the vertical tube and the almost vertical tube types, which are explained next.

Types of centrifuge

Centrifuges generally may be classified into following types:

The horizontal head or swinging buckets type enables the tubes that are inserted into the rotor’s cups to take on a vertical position while the rotor is at rest and a horizontal plane when it is moving. Particles move along the tube during centrifugation in a steady path when the tube is perpendicular to the centrifuge shaft.
As a result, the sediment is evenly dispersed around the tube’s bottom. The sediment’s surface is level. A pipette is used to remove the supernatant liquid with very little disruption to the packed particles. It is perfect for separating a protein precipitate from a solution or erythrocytes from plasma.

Fixed angle or angle head: Tubes are held in a fixed position at angles from 25-40° to the vertical axis of rotation. Particles are driven outward horizontally but strike the side of the tube so that the sediment packs against the side and bottom of the tube with the surface of the sediment paralleled to the shaft of the centrifuge.

As the rotor slows down and stops, gravity causes the sediment to slide down the tube and usually a poorly packed pellet is formed. It allows more rapid sedimentation of small particles as the fixed angle rotors can be run at a higher speed.

Axial type: The axial type is a centrifugal concept that enables the vertical spinning of blood tubes.

Ultracentrifuge: Usually using fixed head rotors, these centrifuges operate at extremely high speeds. utilized mostly to separate ultra-microscopic particles and lipoproteins. They are always equipped with a refrigerated chamber since they produce a significant amount of heat during operation due to friction.

Special types: There are some special types of centrifuges for specific purposes. Mechanically they fall under one of the above-mentioned types. The three most important types are:

• Immunofuge or Serofuge: This type of centrifuge is used in immuno-haematology. It is a horizontal head centrifuge with a fixed tube size head and fixed speed. It is commonly used in blood bank for spinning down the red blood cells.
• Cytospin: This is a horizontal head centrifuge having fixed speed and time. It is provided with special devices in the swinging head, which allow the cells in fluid phase to settle down on a glass slide. Because of the slow speed morphology of the cells is not disturbed. It is used for cytology.
• Blood bag centrifuge: This is also a horizontal head centrifuge but is provided with large buckets to hold blood bags. This is used in preparation of blood components i.e. packed red cells, platelets and plasma etc.
• Gerber centrifuge: This is a special centrifuge. It can hold and spin the Gerber tube, a special glass tube for milk analysis.

Operation

1. Only those tubes that are recommended by the manufacturer of the centrifuge should be used. The tubes should have a tapered bottom, particularly if the supernatant is to be removed.
2. The rotor must be properly balanced. Specimen tubes should be placed on opposite pans of a balance and equalised in weight. The placement of the tubes should also be symmetrical. Tubes filled with water may also be used to equalise the weight. The total weight of each rack should not exceed the limit stated by the centrifuge manufacturer. Imbalance of the rotor causes vibration that may increase wear and tear in the centrifuge and more frequent breakage of the tubes.
3. The lid should then be closed and locked.
4. Required time for centrifugation should be adjusted with the timer knob.
5. The centrifuge should then be switched on and allowed to attain speed for required centrifugation force, which should be adjusted with speed/gravity knob.
6. Lid should not be opened until rotor has completely stopped.

Routine Maintenance

A centrifuge’s need for routine maintenance is influenced by a number of variables, including the technology used, usage volume, operator training, electrical feed quality, and ambient temperatures. To ensure proper operation, the following general guidelines for appropriate use and routine maintenance are provided. The manufacturer’s guidelines for each brand and model will determine the necessary routines or specific fixes.

Before doing any maintenance on centrifuges used to prepare clinical or infectious samples, always clean the rotor bowl, centrifuge head, buckets, and trunnion rings as necessary.
suggestion of priority. Make sure that the centrifuge is only operated by certified individuals who have received training and are knowledgeable about its handling, hazards, and proper use. It is the duty of laboratory directors to oversee and take the appropriate safety measures to ensure that staff members using centrifuges are aware of the risks involved in using such machinery.

Uses of Centrifuge

It separates particulate materials from a solution in which they are suspended. For instance:

• Extracting cell components from blood to produce serum or cell-free plasma for examination.
• Cellular components and other biological fluid constituents are concentrated for microscopic inspection or chemical analysis.
• Removing proteins that have chemically precipitated from an analytical sample.
• Distinguishing the free legend from the protein- or antibody-bound tale in immunochemical or other tests.

Separate two liquid phases with varying densities.

• Aqueous to organic solvents are used to extract solutes from biological fluids.
• Distinguishing lipid components, such as chylomicrons, from lipoproteins and other elements of plasma or serum.