Bench Top Centrifuge – Principle, Types, Parts, Uses

In laboratories, benchtop centrifuges are used to separate and purify molecular mixtures in liquid media depending on their density gradient. Biochemistry laboratories use centrifugation extensively for studying and isolating cells, subcellular fractions, molecular complexes, and biological macromolecules such as proteins, DNA, and RNA. Centrifuges are high-speed devices that require vacuum, gravitational acceleration, and centrifugal force to separate molecules from liquid mixtures without overheating the samples. Nobel Laureate Theodor Svedberg invented the first analytical centrifuge for monitoring sedimentation in 1924. Later, in the 1940s, Claude and his colleagues perfected the centrifugation process, making it the cornerstone of biomedical and biological research for the subsequent decades. Currently, small-capacity benchtop centrifuges are an indispensable instrument for regular biomedical research.

Before centrifugation, the particles are equally distributed in a medium. Upon centrifugation, the denser particles in the medium fall to the bottom, while the lighter particles rise. The top liquid fraction obtained after centrifugation is termed “supernatant.” The portion that sinks to the bottom is known as “pellet.” There is an interaction between the supernatant and the pellet. The particle recovery in the pellet corresponds to the fraction of particles remaining in the pellet after centrifugation. This recovery is contingent upon the particle density and size.

What is Bench top centrifuge?

A benchtop centrifuge is a small, laboratory-grade centrifuge that is designed to be used on a laboratory bench or countertop. It is typically used for separating substances in a liquid or solid mixture by using centrifugal force. This type of centrifuge is commonly used in medical, scientific, and industrial settings for a variety of applications, such as isolating cells or cell components, separating blood components, purifying proteins and nucleic acids, and preparing samples for analysis.

Benchtop centrifuges come in a range of sizes and configurations, and may be powered by electricity or a manual hand crank. They may also have different features and capabilities depending on the model, such as the ability to adjust the speed of the rotor, 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 specific number of revolutions have been completed. Some benchtop centrifuges are designed to be used with a cooling system, while others are suitable for use at room temperature.

Types of Benchtop Centrifuges

There are several types of benchtop centrifuges, including:

1. Microcentrifuges: These are small, lightweight centrifuges that are designed for use with small volumes of liquid, typically in the range of 0.2 to 2 mL. They are commonly used for separating cells, isolating DNA and RNA, and preparing samples for analysis.
2. Mini centrifuges: Even less space is required for mini centrifuges than for regular tabletop centrifuges. They feature a maximum processing capacity of eight tubes and a maximum speed of 6000rpm. While these centrifuges are ideal for laboratories with limited space, they may not be optimal for laboratories with a large production.
3. Plate Centrifuges: Plate centrifuges are predominantly utilised in PCR laboratories. These centrifuges ensure that all reagents are positioned at the bottom of the wells for precise concentrations and outcomes. Plate centrifuges permit a maximum horizontal spin speed of 400xg. To reduce spillage, these benchtop centrifuges have an unusual “wing-out rotor design.”
4. Refrigerated Centrifuges: Temperature-sensitive samples necessitate the use of chilled centrifuges, as even a slight change in temperature can destroy them. These are nearly identical in appearance to their non-refrigerated cousins. However, they permit temperature regulation between -10°C and 40°C.
5. Tabletop centrifuges: These are larger, more heavy-duty centrifuges that are designed for use with larger volumes of liquid, typically in the range of 10 to 100 mL. They are commonly used for separating blood components, purifying proteins, and isolating cell components.
6. High-speed centrifuges: These are powerful centrifuges that are designed for use with high-speed rotors and can achieve very high centrifugal forces. They are commonly used for separating particles in a mixture that are denser or heavier than the surrounding liquid.
7. Refrigerated centrifuges: These are centrifuges that are equipped with a cooling system to keep the samples at a consistent, low temperature during the centrifugation process. They are commonly used for separating biological samples that are sensitive to temperature changes or for working with samples that require storage at low temperatures.
8. Fixed-angle rotor centrifuges: These are centrifuges that have a fixed-angle rotor, which means that the tubes or containers being spun are held at a fixed angle relative to the axis of rotation. They are commonly used for separating particles based on size or density.
9. Swinging bucket rotor centrifuges: These are centrifuges that have a swinging bucket rotor, which means that the tubes or containers being spun are held in a swinging bucket that allows them to change angle relative to the axis of rotation as the rotor spins. They are commonly used for separating particles based on size or density.

Types of Rotors used in Centrifuges

There are several types of rotors that can be used in a centrifuge, including:

1. Fixed-angle rotors: These rotors are designed to hold tubes or containers at a fixed angle relative to the axis of rotation. They are commonly used for separating particles based on size or density.
2. Swinging bucket rotors: These rotors are designed to hold tubes or containers in a swinging bucket that allows them to change angle relative to the axis of rotation as the rotor spins. They are commonly used for separating particles based on size or density.
3. Vertical rotors: These rotors are designed to hold tubes or containers in a vertical orientation, with the axis of rotation running through the center of the tubes. They are commonly used for separating cells or cell components.
4. Horizontal rotors: These rotors are designed to hold tubes or containers in a horizontal orientation, with the axis of rotation running perpendicular to the tubes. They are commonly used for separating blood components or purifying proteins.
5. Zonal rotors: These rotors are designed to hold tubes or containers in a vertical orientation, with the axis of rotation running through the center of the tubes. They are divided into zones, with each zone having a different centrifugal force. They are commonly used for separating cells or cell components based on size or density.

Principle of Benchtop Centrifuges

Substances separate according to their density under the influence of the gravitational force ‘g’ (g = 9.81ms-2) exerted by the Earth’s gravitational field. When these samples receive acceleration in a centrifugal field (G > 9.81ms-2) the sedimentation rate increases. Frequently, the relative gravitational field is represented as a multiple of gravitational acceleration. When using benchtop centrifuges, it is necessary to address underlying factors.

• In a centripetal field, the more dense biomolecules sediment faster.
• The greater a molecule’s mass, the quicker it settles in the centripetal field.
• The biological structure travels slowly in a buffer system with greater density.
• The larger the coefficient of friction, the slower the particle’s velocity.
• At a greater centrifugal force, the particles settle more rapidly.
• When a biomolecule’s density matches that of the surrounding medium, its sedimentation rate becomes null.

The frictional force felt by a biological medium in a viscous media acts in the opposite direction of sedimentation. It is equal to the product of the velocity and frictional coefficient of the particle. As previously established, the centrifugal field is related to the gravitational field of the Earth. The relative centrifugal field (RCF) is the ratio of centrifugal force to standard gravitational acceleration at a given radius and speed. The RCF can be calculated using the following formula:

RCF = G/g = (42rad2 x rpm2 x r) / g

Parts of Benchtop Centrifuges

The parts of a benchtop centrifuge may vary depending on the specific model, but there are some common components that are found in most centrifuges:

1. Rotor: The rotor is the part of the centrifuge that holds the tubes or containers being spun. It is typically made of metal and is mounted on a spindle that allows it to rotate at high speeds.
2. Motor: The motor is the part of the centrifuge that powers the rotor. It may be an electric motor or a manual hand crank, depending on the model.
3. Control panel: The control panel is the part of the centrifuge that allows the user to set and adjust the centrifuge parameters, such as the speed, time, and temperature.
4. Lid: The lid is the part of the centrifuge that covers the rotor and helps to contain the samples during the centrifugation process.
5. Safety interlock: The safety interlock is a mechanism that prevents the centrifuge from being started if the lid is not properly secured or if the rotor is not properly balanced.
6. Timer: The timer is a device that allows the user to set the desired length of time for the centrifugation process.
7. Temperature control system: Some benchtop centrifuges are equipped with a temperature control system that allows the user to set and maintain a specific temperature during the centrifugation process.
8. Display: The display is a screen or panel that shows the current status of the centrifuge, such as the speed, time, and temperature.
9. Sample tubes or containers: The sample tubes or containers are the vessels that hold the samples being spun in the centrifuge. They may be made of glass, plastic, or other materials and come in a range of sizes and shapes.

Operating Procedure of Benchtop Centrifuges

The protocol for using a benchtop centrifuge will depend on the specific model and the intended application. However, there are some general steps that are followed when using a benchtop centrifuge:

1. Prepare the samples: Depending on the specific application, the samples may need to be prepared in a specific way. For example, they may need to be diluted, mixed with a buffer solution, or placed in a specific type of container.
2. Load the samples into the rotor: Carefully load the samples into the rotor according to the manufacturer’s instructions. Make sure that the samples are evenly balanced and that the rotor is properly balanced.
3. Secure the rotor: Secure the rotor in place according to the manufacturer’s instructions. This may involve locking it into place, attaching a lid, or securing it with a clamp.
4. Set the centrifuge parameters: Set the desired centrifuge parameters, such as the speed, time, and temperature, according to the manufacturer’s instructions.
5. Start the centrifuge: Start the centrifuge by pressing the appropriate button or flipping the appropriate switch. Make sure that the centrifuge is stable and that the samples are not being subjected to any excessive vibrations.
6. Monitor the centrifuge: Monitor the centrifuge during the centrifugation process to ensure that it is running smoothly and that the samples are not being subjected to any excessive forces.
7. Shut off the centrifuge: When the centrifugation process is complete, shut off the centrifuge and carefully remove the rotor.
8. Dispose of the samples: Dispose of the samples according to the appropriate protocols. For example, biological samples may need to be treated as hazardous waste.
9. Clean the centrifuge: Clean the centrifuge according to the manufacturer’s instructions. This may involve wiping down the exterior, cleaning the rotor and other internal parts, and sanitizing the machine.

Applications of Benchtop Centrifuges

Benchtop centrifuges are widely used in a variety of applications in the medical, scientific, and industrial fields, including:

1. Separating cells or cell components: Benchtop centrifuges can be used to separate different types of cells or cell components, such as red blood cells, white blood cells, and platelets. They can also be used to isolate specific cell organelles, such as mitochondria or nuclei.
2. Separating blood components: Benchtop centrifuges can be used to separate the different components of blood, such as red blood cells, white blood cells, and plasma. This is commonly done to prepare blood for transfusions or to analyze specific components of the blood.
3. Purifying proteins: Benchtop centrifuges can be used to purify proteins from complex mixtures, such as cell lysates or protein extracts. This is commonly done to prepare proteins for further analysis or to purify them for use in research or industry.
4. Isolating DNA and RNA: Benchtop centrifuges can be used to isolate DNA and RNA from biological samples, such as cells or tissue. This is commonly done to prepare samples for genetic analysis or to use the DNA or RNA in research or biotechnology applications.
5. Preparing samples for analysis: Benchtop centrifuges can be used to prepare samples for a variety of analytical techniques, such as microscopy, spectroscopy, or chromatography.
6. Separating particles in a mixture: Benchtop centrifuges can be used to separate particles in a mixture based on size or density. This is commonly done to purify or isolate specific components of a mixture.
7. Sedimentation: Benchtop centrifuges can be used to separate solid particles from a liquid by sedimentation. This is commonly done to purify or isolate specific components of a mixture.
8. Clarification: Benchtop centrifuges can be used to clarify liquids by removing impurities or suspended particles. This is commonly done to prepare liquids for further analysis or to remove contaminants.

Advantages of Benchtop Centrifuges

There are several advantages to using a benchtop centrifuge over other types of centrifuges, such as:

1. Size: Benchtop centrifuges are smaller and more compact than other types of centrifuges, making them easier to use in laboratory settings where space is limited.
2. Versatility: Benchtop centrifuges are versatile and can be used for a wide range of applications, from separating cells to purifying proteins.
3. Convenience: Benchtop centrifuges are easy to use and can be easily moved from one location to another, making them convenient for a variety of applications.
4. Cost: Benchtop centrifuges are generally less expensive than other types of centrifuges, making them an affordable option for many laboratories.
5. Safety: Benchtop centrifuges are designed with safety features, such as a safety interlock to prevent the machine from being started if the lid is not properly secured or if the rotor is not properly balanced.
6. Precision: Benchtop centrifuges can achieve precise results, making them suitable for applications that require high accuracy.
7. Efficiency: Benchtop centrifuges are efficient and can process large numbers of samples quickly and efficiently, saving time and resources.

Disadvantages of Benchtop Centrifuges

1. Capacity: Benchtop centrifuges typically have a smaller capacity than other types of centrifuges, making them less suitable for large-scale processing.
2. Speed: Benchtop centrifuges may not be able to achieve the same high speeds as other types of centrifuges, making them less suitable for some applications that require very high centrifugal forces.
3. Power: Benchtop centrifuges may not be as powerful as other types of centrifuges, making them less suitable for some applications that require very high centrifugal forces.
4. Noise: Some benchtop centrifuges may be louder than other types of centrifuges, which can be an issue in settings where noise is a concern.
5. Cost: Although benchtop centrifuges are generally less expensive than other types of centrifuges, they can still be a significant financial investment for some laboratories.
6. Maintenance: Benchtop centrifuges may require more frequent maintenance than other types of centrifuges, which can be time-consuming and costly.

Precautions for operating Benchtop Centrifuges

There are several precautions to consider when operating a benchtop centrifuge:

1. Follow the manufacturer’s instructions: Always read and follow the manufacturer’s instructions carefully when using a benchtop centrifuge. This will help to ensure that the machine is used safely and correctly.
2. Leveled surface: Ensure that the centrifuge is positioned on a balanced/level surface prior to initiating the experiment.
3. Use the appropriate samples and tubes: Use the appropriate samples and tubes for the specific application and rotor being used. Using the wrong type of samples or tubes can damage the machine or result in inaccurate results.
4. Lid: Before processing, ensure that the lids of the centrifuge tubes are properly secured, as any leakage can lead to sample cross-contamination. Do not open the cover while the rotor is in operation. After the centrifuge cycle is complete, the lid should not be opened until the rotor has slowed to a stop.
5. Secure the samples and rotor: Make sure that the samples and rotor are securely fastened in place before starting the centrifuge. This will help to prevent accidents or injuries.
6. Use appropriate personal protective equipment: When working with hazardous materials, make sure to use appropriate personal protective equipment, such as gloves, goggles, and a lab coat.
7. Balance the rotor: Balance the tubes in the centrifuge at all times. For example, if you need to centrifuge a 5ml tube, place another 5ml tube in the opposite hole on the rotor. If no sample tubes are available, water-filled centrifuge tubes should be used. However, if the liquid’s density is greater or less than that of water, the tubes must be balanced by mass, not by volume. Unbalanced centrifuges can cause injury or equipment damage.
8. Use caution when handling the rotor: When handling the rotor, use caution to avoid getting injured or spilling the samples. The rotor can be very heavy and may contain sharp edges.
9. Keep the centrifuge clean: Regularly clean and maintain the centrifuge to ensure that it is in good working condition. This may involve wiping down the exterior, cleaning the rotor and other internal parts, and sanitizing the machine.
10. Follow proper disposal procedures: When disposing of samples, make sure to follow proper disposal procedures to prevent contamination or accidents. For example, biological samples may need to be treated as hazardous waste.
11. If the centrifuge is swaying or trembling, stop it immediately and verify that the tubes are balanced. A minor vibration is normal, but centrifugation ceases if the shaking persists.

Top 5 and best Benchtop Centrifuges – Benchtop Centrifuges Examples

It is difficult to recommend specific brands or models of benchtop centrifuges as the best option, as the ideal centrifuge will depend on the specific needs and preferences of the user. Here are five popular brands that offer a range of benchtop centrifuges:

1. Thermo Scientific: This company offers a wide range of benchtop centrifuges, including microcentrifuges, tabletop centrifuges, and high-speed centrifuges.
2. Eppendorf: This company offers a range of microcentrifuges and tabletop centrifuges that are suitable for a variety of applications, including cell separation, DNA isolation, and protein purification.
3. Sigma-Aldrich: This company offers a range of benchtop centrifuges, including microcentrifuges, tabletop centrifuges, and refrigerated centrifuges.
4. Hettich: This company offers a range of benchtop centrifuges, including microcentrifuges, tabletop centrifuges, and high-speed centrifuges.
5. Beckman Coulter: This company offers a range of benchtop centrifuges, including microcentrifuges, tabletop centrifuges, and high-speed centrifuges.