Principles and Types of Bench Top Centrifuges

Benchtop centrifuges are used in laboratories to separate and filter molecular mixtures in liquid media based on their density gradient. Centrifugation is widely used in biochemistry laboratories for investigating and isolating cells, subcellular fractions, molecular complexes, and biological macromolecules such as proteins, DNA, and RNA. Centrifuges are high-speed machines that use vacuum, gravitational acceleration, and centrifugal force to separate molecules from liquid mixtures while avoiding scorching the samples. In 1924, Nobel Laureate Theodor Svedberg invented the first analytical centrifuge for sediment monitoring. Later, in the 1940s, Claude and his colleagues refined the centrifugation method, which became the foundation of biomedical and biological research over the next few decades. Small-capacity benchtop centrifuges are becoming an essential tool for routine biomedical research.

The particles are evenly disseminated in a medium prior to centrifugation. The denser particles in the medium sink to the bottom during centrifugation, while the lighter particles rise. The top liquid fraction obtained following centrifugation is referred to as “supernatant.” The part that sinks to the bottom is referred to as “pellet.” The supernatant and the pellet have an interaction. The fraction of particles left in the pellet after centrifugation is referred to as particle recovery. This recovery is affected by particle density and size.

What exactly is a bench top centrifuge?

A benchtop centrifuge is a tiny, laboratory-grade centrifuge intended for use on a laboratory bench or countertop. Centrifugal force is commonly employed to separate substances in a liquid or solid mixture. This type of centrifuge is extensively used in medical, scientific, and industrial contexts to isolate cells or cell components, separate blood components, purify proteins and nucleic acids, and prepare samples for analysis.

Benchtop centrifuges are available in a variety of sizes and configurations, and can be powered by electricity or a hand crank. Depending on the model, they may also have different features and capabilities, such as the ability to adjust the rotor speed, the capacity to hold different types of tubes or other containers, and the ability to run for a specific amount of time or until a certain number of revolutions have been completed. Some tabletop centrifuges are intended to be used in conjunction with a cooling system, while others can be operated at room temperature.

Benchtop Centrifuge Types

Benchtop centrifuges are classified into numerous categories, including:

• Microcentrifuges: These are small, lightweight centrifuges designed to handle small amounts of liquid, typically 0.2 to 2 mL. They are often employed for cell separation, DNA and RNA isolation, and sample preparation for analysis.
• Mini centrifuges: Mini centrifuges take up even less area than ordinary tabletop centrifuges. They have an eight-tube maximum processing capacity and a maximum speed of 6000rpm. These centrifuges are great for laboratories with limited space, however they may not be appropriate for laboratories with high production.
• Plate Centrifuges: Plate centrifuges are widely used in PCR laboratories. These centrifuges make certain that all reagents are placed to the bottom of the wells for accurate concentrations and results. A maximum horizontal spin speed of 400xg is possible with plate centrifuges. To avoid spillage, these benchtop centrifuges use a distinctive “wing-out rotor design.”
• Refrigerated Centrifuges: Temperature-sensitive samples require cooled centrifuges since even minor temperature changes can destroy them. These seem nearly identical to their non-refrigerated cousins. They do, however, allow temperature adjustment between -10°C and 40°C.
• Tabletop centrifuges: These are larger, heavier-duty centrifuges designed for use with larger amounts of liquid, typically 10 to 100 mL. They are frequently utilized in the separation of blood components, the purification of proteins, and the isolation of cell components.
• High-speed centrifuges: These are powerful centrifuges with high-speed rotors that can achieve extremely high centrifugal forces. They are typically employed to separate particles that are denser or heavier than the surrounding liquid in a combination.
• Refrigerated centrifuges: Refrigerated centrifuges are those that have a cooling system that keeps the samples at a consistent, low temperature during the centrifugation process. They are widely employed for separating biological samples that are temperature sensitive or for working with samples that require low-temperature storage.
• Centrifuges with fixed-angle rotors: These have a fixed-angle rotor, which implies that the tubes or containers being spun are held at a fixed angle relative to the axis of rotation. They are frequently employed for particle separation based on size or density.
• Swinging bucket rotor centrifuges: These centrifuges have a swinging bucket rotor, which allows the tubes or containers being spun to vary angle relative to the axis of rotation while the rotor rotates. They are frequently employed for particle separation based on size or density.

Different types of centrifuge rotors

In a centrifuge, numerous types of rotors can be employed, including:

1. Fixed-angle rotors: Set-angle rotors are intended to hold tubes or containers at a set angle relative to the axis of rotation. They are frequently employed for particle separation based on size or density.
2. Swinging bucket rotors: Swinging bucket rotors are designed to hold tubes or containers in a swinging bucket, allowing them to alter angle relative to the axis of rotation as the rotor spins. They are frequently employed for particle separation based on size or density.
3. Vertical rotors: Vertical rotors are intended to hold tubes or containers vertically, with the axis of rotation passing through the center of the tubes. They’re frequently employed to separate cells or cell components.
4. Horizontal rotors: Horizontal rotors are intended to hold tubes or containers horizontally, with the axis of rotation running perpendicular to the tubes. They are frequently used to separate blood components or to purify proteins.
5. Zonal rotors: These rotors are meant to support vertical tubes or containers, with the axis of rotation passing through the center of the tubes. They are separated into zones, each with its own centrifugal force. They’re frequently employed to separate cells or cell components based on size or density.

Benchtop Centrifuge Principle

The gravitational force ‘g’ (g = 9.81ms-2) exerted by the Earth’s gravitational field causes substances to separate based on their density. The sedimentation rate increases when these samples are accelerated in a centrifugal field (G > 9.81ms-2). The relative gravitational field is frequently represented as a multiple of gravitational acceleration. When employing benchtop centrifuges, underlying factors must be addressed.

• The more dense biomolecules sediment faster in a centripetal field.
• The larger the mass of a molecule, the faster it settles in the centripetal field.
• The biological structure moves slowly via a more dense buffer system.
• The particle’s velocity decreases as the coefficient of friction increases.
• Particles settle faster under higher centrifugal forces.
• When the density of a biomolecule matches that of the surrounding medium, its sedimentation rate becomes zero.

A biological medium’s frictional force in a viscous medium acts in the opposite direction of sedimentation. It is equal to the product of the particle’s velocity and frictional coefficient. As previously stated, the centrifugal field is related to the Earth’s gravitational field. At a given radius and speed, the relative centrifugal field (RCF) is the ratio of centrifugal force to standard gravitational acceleration.