Centrifuge – Principle, Parts, Types, Operation, Applications and Advantages

Introduction

• A centrifuge is an essential piece of laboratory equipment used to separate mixtures of liquids, or solids suspended in liquids, based on differences in density.
• It operates by spinning samples at high speeds, creating a centrifugal force that pushes denser particles outward and lighter particles inward.
• In biology and chemistry laboratories, centrifuges are widely used for separating blood components, DNA and RNA, proteins, cell organelles, and microscopic particles.
• Outside laboratories, centrifuges have industrial applications in dairy production, wastewater treatment, pharmaceuticals, mining, and aerospace training.
• The concept of centrifugal separation dates back to the late 19th century, with early designs being used for separating cream from milk.
• Today, centrifuges range from small benchtop models for basic lab work to ultracentrifuges capable of spinning at extremely high speeds to separate nanoscale particles like viruses.

Principle of Centrifugation

• Centrifugation is based on the sedimentation principle, which states that particles in a fluid will settle under the influence of gravity or centrifugal force.
• Centrifugal force is much stronger than gravity and is generated when an object is rotated at high speed.
• When a sample is spun:
  • Heavier particles move toward the outer edge (bottom of tube).
  • Lighter particles remain near the center (top of tube).
• The rate of sedimentation depends on:
  • Particle size and shape
  • Density difference between particle and medium
  • Viscosity of the medium
  • Applied rotational speed (rpm) or relative centrifugal force (RCF)
• In normal gravity, it might take hours for small particles to settle. In a centrifuge, separation can happen in minutes.

Main Components of a Centrifuge

1. Motor
   • Powers the rotation of the rotor.
   • Modern centrifuges have variable speed motors with electronic control.
2. Rotor
   • The spinning part that holds the samples.
   • Types of rotors:
     • Fixed-Angle Rotor – Holds tubes at a constant angle (14–40°). Good for pelleting cells and precipitates.
     • Swinging-Bucket Rotor – Tubes swing horizontally during spinning. Ideal for density gradient separations.
     • Vertical Rotor – Tubes remain vertical. Used mainly for isopycnic centrifugation.
3. Sample Holders
   • Test tubes, bottles, or microcentrifuge tubes where samples are placed.
   • Made of plastic, glass, or metal depending on application.
4. Drive Shaft
   • Connects the rotor to the motor.
5. Control Panel
   • Lets the user set speed (rpm or RCF), time, and sometimes temperature.
6. Lid and Lock
   • Ensures safety by preventing the lid from opening while spinning.
7. Refrigeration System (in refrigerated centrifuges)
   • Keeps temperature low to prevent heat damage to biological samples.

Types of Centrifugation Techniques

1. Differential Centrifugation

• Separates particles based on size and density by spinning at progressively higher speeds.
• Steps:
  1. Low speed → removes large debris.
  2. Higher speed → sediments smaller organelles.
• Used for separating nuclei, mitochondria, lysosomes, and ribosomes.

2. Density Gradient Centrifugation

• Separates particles based on buoyant density using a density gradient medium (e.g., sucrose, cesium chloride).
• Two types:
  • Rate-Zonal Centrifugation – Separation based on size and mass.

• Isopycnic Centrifugation – Separation based solely on density.

3. Analytical Centrifugation

• Used for studying properties of molecules such as sedimentation rate, molecular weight, and shape.

Types of Centrifuges

1. Benchtop / Tabletop Centrifuge
   • Small, portable, for general lab work.
2. Microcentrifuge
   • For small volumes (0.2–2 ml); used in molecular biology.
3. Refrigerated Centrifuge
   • Maintains low temperatures for sensitive samples.
4. High-Speed Centrifuge
   • Speeds up to 30,000 rpm.
5. Low-Speed Centrifuge
   • Up to 5,000 rpm; used for routine separations.
6. Continuous Flow Centrifuge
   • Separates large volumes without stopping.
7. Ultracentrifuge
   • Up to 150,000 rpm; used for viruses, ribosomes, macromolecules.
   • Preparative Ultracentrifuge – For sample isolation.
   • Analytical Ultracentrifuge – For studying sample properties.
8. Haematocrit Centrifuge
   • Measures red blood cell volume in blood samples.
9. Gas Centrifuge
   • Separates isotopes and gases (e.g., uranium enrichment).

Step-by-Step Operation of Centrifuge

1. Inspect centrifuge and ensure cleanliness.
2. Select appropriate rotor and sample tubes.
3. Fill tubes equally and balance by weight.
4. Place tubes opposite each other in rotor.
5. Close lid securely.
6. Set speed, time, and temperature (if applicable).
7. Start centrifuge and monitor.
8. Wait until rotor stops completely before opening.
9. Remove samples carefully.

Applications of Centrifuge

In Biology and Medicine

• Blood component separation (plasma, serum, platelets).
• Isolation of DNA, RNA, and proteins.
• Separation of cell organelles for biochemical analysis.
• Concentration of viruses and bacteria for research.

In Industry

• Dairy: Separating cream from milk.
• Pharmaceuticals: Drug purification and formulation.
• Water treatment: Removing suspended solids.

In Research

• Studying sedimentation behavior of macromolecules.
• Purifying enzymes and hormones.

In Forensics

• Isolating DNA from crime scene samples.

In Aerospace

• Human centrifuges used to train pilots under high g-forces.

Advantages of Centrifuge

• Fast and efficient separation.
• Suitable for a wide range of samples.
• Adjustable settings for different needs.
• Can process multiple samples at once.

Limitations of Centrifuge

• Expensive for high-end models.
• Requires trained operators.
• Can be noisy and generate heat.
• Risk of aerosol generation with biological samples.

Precautions

• Always balance tubes before starting.
• Keep lid locked during operation.
• Do not exceed recommended rotor speed.
• Use appropriate PPE (gloves, goggles).

Recent Innovations

• Automatic imbalance detection.
• Digital controls with memory settings.
• Low-noise motors.
• Integration with cloud data logging.

Frequently Asked Questions (FAQ)

Q1. What is the main function of a centrifuge?
It separates mixtures by spinning them at high speed, causing denser particles to move outward and lighter particles to remain near the center.

Q2. What is RCF in centrifugation?
RCF (Relative Centrifugal Force) is the force exerted on samples, calculated using rpm and rotor radius.

Q3. What is the difference between ultracentrifuge and microcentrifuge?
An ultracentrifuge reaches much higher speeds for separating very small particles like viruses, while a microcentrifuge is for small-volume lab work.

Q4. Can centrifuges be used for gases?
Yes, gas centrifuges separate isotopes and gas mixtures.

Q5. Why is balancing tubes important?
Imbalance can cause vibration, noise, and damage to the centrifuge, and may even cause accidents.

Q6. Who invented the centrifuge?
Early centrifuge designs were developed in the late 19th century, with Wilhelm Prandtl creating one of the first milk separators.

References

1. https://study.com/academy/lesson/what-is-centrifugation-definition-process-uses.html
2. https://www.toppr.com/guides/chemistry/is-matter-around-us-pure/centrifugation/
3. https://microbiologynote.com/ultracentrifuge-definition-principle-types-uses/
4. https://www.ehs.uci.edu/sop/hazardous-operations/centrifuge-sop.pdf
5. https://www.medicalexpo.com/prod/eppendorf-se/product-68382-849100.html
6. https://www.medicalexpo.com/prod/cryste/product-105953-1030380.html
7. https://www.medicalexpo.com/prod/lepu-medical-technology/product-95737-988153.html