Understanding Centrifugation: Definition, Principle and Process

Centrifugation is a pivotal technique in both scientific research and medical laboratories, employed to separate and analyze components of a mixture based on their density. By applying rapid rotational force, centrifugation effectively isolates substances such as cells, proteins, and other particles from liquids, facilitating a wide array of applications from clinical diagnostics to biochemical research. This process enhances our ability to study complex samples with precision and efficiency. In this blog, we will explore the principles behind centrifugation, the different types available, its key objectives, and its broad applications. Additionally, we will review various brands of centrifugation equipment available on Medikabazaar, helping you choose the right tool for your laboratory needs.

What is Centrifugation?             

Let’s understand what centrifugation is. Centrifugation is a method used to separate particles from a solution based on their size, shape, density, viscosity of the medium, and rotor speed. In this process, particles suspended in a liquid medium are placed in a centrifuge tube, which is then positioned in a rotor and spun at a high speed. While sedimentation under gravity is a natural process, it is significantly slower. Centrifugation accelerates this process by generating a centrifugal force through the rotation of the rotor, which swiftly separates the particles based on their density.

Principle of Centrifugation:

Centrifugation is a technique used to separate particles using a centrifugal field, which causes denser particles to settle at the bottom of the tube while less dense substances rise to the top. In this process, the denser components migrate away from the axis of rotation, while lighter components move toward it. The instrument used for centrifugation is called a centrifuge, consisting of three basic components: a rotor, a drive shaft, and a motor.

The rotor holds the tubes or bottles containing the liquids to be centrifuged. Different types and sizes of rotors can be mounted on the drive shaft, which is connected to the motor that powers the rotation. As the rotor spins, it generates centrifugal force on the particles in the suspension, counteracted by buoyant and frictional forces. When the centrifugal force exceeds these opposing forces, sedimentation occurs.

The rate of sedimentation depends on factors such as the applied centrifugal field, particle size, density, radius, and the density and viscosity of the suspending medium. Centrifugation speed is expressed in revolutions per minute (RPM), determined by angular velocity (ω). The centrifugal force (F) is calculated using the formula:

F=mω2rF=mω2r

Where:

• mm = effective mass of the sedimenting particles,
• ωω = angular velocity of rotation in rad/sec,
• rr = distance of the particles from the axis of rotation.

The force on the sedimenting particles increases with the velocity of rotation and the distance from the axis. A more common measurement, Relative Centrifugal Force (RCF), is expressed in terms of the earth’s gravitational force (g) and calculated as:

RCF=(1.119×10−5)(rpm)2(r)RCF=(1.119×10−5)(rpm)2(r)

For instance, if a rotor with an average radius of 8 cm spins at 20,000 rpm, the relative centrifugal force (RCF) generated is 35,800 g.

Different Types of Centrifugation:

The types of centrifuge are discussed below.

Density Gradient Centrifugation

Density gradient centrifugation is a powerful technique used to separate and measure the components of a mixture based on their density. This method is further divided into two types:

• Rate Zonal Centrifugation: In this method, a solution with a density gradient is prepared, and the sample, which has a density greater than all layers of the gradient, is placed in a thin zone at the top of the centrifuge tube. Under centrifugal force, particles begin to separate through the gradient, forming distinct zones based on their size, shape, and density.
• Isopycnic or Sedimentation Equilibrium Centrifugation: Here, the solution has a broader range of densities, encompassing the entire range of densities of the particles in the sample. Each particle migrates to the point in the centrifuge tube where the gradient density matches its own density. In this method, separation occurs based on density differences, independent of time.

Differential Centrifugation:

Differential centrifugation is widely used in microbiology and cytology for separating specific cell organelles for further analysis. The process begins by homogenizing a tissue sample to break cell membranes and mix cell contents. The resulting homogenate is subjected to repeated centrifugation, each time removing the pellet and increasing the centrifugal force. This method allows for the stepwise isolation of organelles based on their size and density.

Ultracentrifugation:

Ultracentrifugation is an advanced technique developed by chemist Svedberg, who used it to determine the molecular weight and subunit structure of haemoglobin. The first commercial ultracentrifuge was produced in 1940. This technique imposes high centrifugal forces on suspended particles or molecules in solution, enabling their separation based on differences in weight. Ultracentrifugation is essential in biochemical research for separating red blood cells from plasma, nuclei from mitochondria, and proteins in complex mixtures.

Objectives of Centrifugation:

Application of Centrifugal Force: Centrifugation utilizes centrifugal force, which is the force that acts outward on a body moving around a center, arising from the body's inertia. In the context of centrifugation, this force is applied by rapidly spinning a sample around a fixed axis. The high-speed rotation generates a force many times greater than gravity, effectively pushing particles outward and away from the axis of rotation. This force drives the separation process by causing particles within the mixture to move according to their relative densities.

Separation Based on Physical Properties: The separation of particles in a centrifuge is influenced by several key physical properties.

• Size: Larger particles experience a greater centrifugal force and thus move more rapidly to the bottom of the centrifuge tube.
• Shape: The shape of the particles can also affect how they move through the medium. More streamlined particles may settle more quickly than irregularly shaped ones.
• Density: Denser particles migrate outward faster, separating more quickly from lighter particles.
• Viscosity of the Medium: The viscosity of the liquid medium, or its resistance to flow, impacts the rate of sedimentation. A higher viscosity medium slows the movement of particles.
• Rotor Speed: The speed of rotation, typically measured in revolutions per minute (RPM), is directly proportional to the centrifugal force. Higher speeds result in more efficient separation, especially for small or less dense particles.

Spinning at High Speed: The separation process in centrifugation is achieved by placing the sample in a centrifuge and spinning it at high speeds. The rapid rotation creates a powerful centrifugal force that causes the denser particles to be pushed outward toward the periphery of the vessel, while lighter particles remain closer to the center. This spinning motion mimics and greatly accelerates the natural sedimentation process that would occur under the influence of gravity alone, enabling faster and more efficient separation.

Role of a Centrifuge: A centrifuge is the laboratory device used to perform centrifugation. It consists of several components that work together to apply the necessary forces.

• Rotor: The part of the centrifuge that holds the tubes or containers with the sample. Different types of rotors, such as fixed-angle or swinging-bucket, can be used depending on the specific application.
• Motor: The motor drives the rotation of the rotor at high speeds, providing the necessary centrifugal force to separate the particles.
• Control Panel: Modern centrifuges are equipped with control panels that allow users to set and monitor parameters such as speed, time, and temperature, ensuring precise and reproducible results.

Centrifuges are used in a wide range of applications, from separating blood components in medical diagnostics to purifying proteins and nucleic acids in molecular biology, as well as in the separation of immiscible fluids, such as oil and water, in chemical and industrial processes.

Separation of Immiscible Fluids: In addition to separating solid particles from liquids, centrifuges are also employed to separate immiscible fluids, such as oil and water, or to separate different phases in a mixture of liquids and gases. The centrifugal force effectively separates these fluids based on their density differences, with the denser fluid moving outward and the lighter fluid remaining closer to the center. This process is essential in various industrial applications, including the purification of chemical compounds, the treatment of wastewater, and the refinement of crude oil.

Process of Centrifugation:

A centrifuge is a machine equipped with a rotor that is used to separate particles from a solution. In biological contexts, these particles can include cells, subcellular organelles, or large molecules—all collectively referred to as particles.

There are two primary centrifugation techniques: preparative centrifugation, aimed at isolating specific particles, and analytical centrifugation, focused on determining the physical properties of the particles being separated. As the centrifuge’s rotor spins, each particle within the sample experiences a centrifugal force, which drives their sedimentation at a rate proportional to their properties.

The sedimentation rate of particles is influenced not only by the centrifugal force but also by the physical characteristics of the particles themselves and the viscosity of the sample solution. Specifically, the sedimentation rate is directly proportional to the size (molecular weight) of the particle and the difference in density between the particle and the surrounding solution, provided that the centrifugal force and liquid viscosity remain constant.

Applications of Centrifugation:

• Production of bulk drugs.
• Production of biological products.
• Evaluation of suspensions and emulsion.
• Determination of molecular weight of collides.
• Separating chalk powder from water.
• Removing fat from milk to produce skimmed milk.
• The clarification and stabilization of the wine.
• Biopharmaceutical analysis of drugs.
• Use in water treatment.
• Removing water from lettuce after washing it in a salad spinner.
• Separating particles from an airflow using cyclonic separation.

Different Brands Available on Medikabazaar:

Some popular centrifuge brands featured on Medikabazaar include:

Remi bench Top Clinical Centrifuge: Known for durable and versatile centrifuges, ideal for various laboratory applications, including clinical and research settings.

Remi Revolutionary General Purpose Centrifuge: Offers versatile performance with high-speed capabilities for a wide range of applications. Suitable for both clinical and research use.

Electra-BL Laboratory Centrifuge: Provides reliable and precise separation with user-friendly controls. Ideal for routine laboratory tasks and applications requiring consistent results.

Remi Mini Centrifuge: Compact and efficient, perfect for small sample volumes and quick spin-downs. Convenient for use in space-limited lab settings.

Remi Microprocessor Laboratory Centrifuge: Features advanced microprocessor control for precise speed and time settings. Suitable for high-precision tasks and demanding laboratory needs.

Thermo Scientific: Offers high-performance centrifuges with advanced features, suitable for sophisticated research labs.

Eppendorf: Renowned for precision and reliability, Eppendorf centrifuges are widely used in molecular biology and clinical labs.

Neuation: Provides cost-effective centrifuge solutions with user-friendly designs, ideal for routine lab use.

In conclusion, centrifugation is a vital technique in various scientific and industrial fields, enabling the efficient separation of particles based on their size, density, and other properties. Whether used for preparative or analytical purposes, centrifugation is fundamental in laboratories worldwide. The availability of a wide range of centrifuges, from brands like Remi, Thermo Scientific, Eppendorf, and Neuation, ensures that laboratories can find the right equipment to meet their specific needs. As technology advances, centrifugation will continue to play a crucial role in scientific discovery and industrial processes.