Basics of Centrifugation

Centrifugation is a process that uses centrifugal force to separate different components of a mixture. A centrifuge generates centrifugal force through high-speed rotation, which separates particles or molecules in a sample based on their density differences. During centrifugation, heavier components sediment to the bottom, while lighter components remain in the upper layers.

Working Principle of Lab Centrifuges

Basic Concept of Centrifugal Force

Centrifugal force is the apparent force generated by the rotation of the sample within a lab centrifuge. It is related to the mass of the sample and the rotational speed. The magnitude of centrifugal force is significantly greater than the force of gravity (g-force), which facilitates the separation of components with different densities within the sample. During centrifugation, centrifugal force pushes particles in the sample towards different regions of the centrifuge tube based on their density differences. The formula for calculating centrifugal force is:

Fc=m⋅ω²⋅r

where Fc is the centrifugal force, mis the mass of the particle, ris the radial distance from the axis of rotation, and ωis the angular velocity.

Role of the Rotor and Fixed Shaft

The core components of a lab centrifuge include the rotor and the fixed shaft.

• Rotor

The rotor is the rotating component where samples are placed in centrifuge tubes or cups. Driven by a motor, the rotor spins at high speeds around the fixed shaft. The rotor is responsible for accelerating the samples, generating centrifugal force. The design and type of the rotor, such as an angle rotor or a horizontal rotor, affect the efficiency and effectiveness of the centrifugation process. The rotor contains multiple sample slots to accommodate several tubes, allowing for simultaneous processing of multiple samples.

• Fixed Shaft

The fixed shaft serves as the central axis of rotation for the rotor, ensuring that the rotor maintains a stable and consistent rotational path. It also absorbs the mechanical stresses generated during the lab centrifuge operation and maintains the balance of the rotor.

Main Types of Centrifugation

Isopycnic Centrifugation

Isopycnic centrifugation is a technique that separates samples using a balanced density gradient. By establishing a self-generated density gradient within the centrifuge tube, components of the sample are positioned at different points along the gradient according to their relative densities. This method is suitable for separating molecules with similar densities but different structures or functions, such as different types of cells or viruses in biological research.

Density Gradient Centrifugation

Density gradient centrifugation involves setting up a medium with a gradient density (such as a sucrose solution or cesium chloride) in the centrifuge tube. During centrifugation, the sample components settle at positions in the gradient that match their densities. This technique is especially effective for separating components with a wide range of densities, such as organelles and nucleic acids.

Phase Separation

Phase separation is a technique that uses centrifugal force to separate different phases within a sample. In this process, chemical substances in the sample transfer from a matrix or aqueous phase to a layered organic solvent phase or other phases. This method is commonly used in analytical chemistry and biological experiments for further molecular analysis or processing.

Pelleting

Pelleting is an application of centrifugation used to separate and concentrate particles or precipitates from a liquid. The centrifugal force causes particles to sediment at the bottom of the centrifuge tube, while the liquid (supernatant) remains above. This method is frequently employed to separate cell pellets, protein complexes, or other solid particles, and is widely used in biopharmaceutical and laboratory research.

Centrifugation Protocols and Parameters

Relative Centrifugal Force (rcf)

Relative Centrifugal Force (rcf) measures the centrifugal force applied to a sample during centrifugation. It is related to the actual acceleration experienced by the sample in the centrifuge and is typically expressed as a multiple of the force of gravity (g-force). Rcf is a key parameter in calculating centrifugal force and helps determine the separation efficiency of different components. The calculation formula is:

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where rpm is the rotational speed in revolutions per minute, r is the radius from the axis of rotation to the sample, and g is the acceleration due to gravity.

Acceleration (g-force)

Acceleration (g-force) represents the acceleration experienced by the sample during centrifugation relative to the gravitational force at Earth’s surface. This parameter determines the sedimentation rate of different components in the sample, thereby affecting the separation efficiency. Higher acceleration leads to stronger centrifugal force and faster separation. The required acceleration is usually specified in the centrifugation protocol to ensure effective sample separation.

Rotational Speed （rpm）

Rotational speed (revolutions per minute, rpm) is the speed at which the centrifuge rotor spins, directly influencing the magnitude of the centrifugal force. It is an important parameter for adjusting centrifugal force and is typically specified in the centrifugation protocol. Higher rpm generates greater centrifugal force but requires that the rotor and centrifuge can withstand the increased speed. Although rpm is related to centrifugal force, using rcf is more precise for calculating the exact force applied.The rotational speed (rpm) can be calculated from rcf using the following formula:

Industrial centrifuges

Industrial centrifuges are engineered for large-scale separation and processing, playing a crucial role in industries such as chemicals, food production, pharmaceuticals, and environmental engineering. Designed to handle substantial volumes, these machines combine efficiency and durability, featuring expansive rotors and powerful drive systems to manage heavy loads and extended operation times.

Huading Separator offers a range of industrial centrifuges, including high-efficiency solid-liquid separators, centrifuge dewatering machines, and separators. These devices achieve efficient separation and reliable performance through optimized design and advanced technology. They are suitable for processing various liquid and solid mixtures, such as slurry, wastewater, and food processing by-products, contributing to improved production efficiency and product quality. The design of these industrial centrifuges not only focuses on performance but also emphasizes operational safety and ease of maintenance.

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