- Centrifugation is a powerful laboratory technique that separates particles based on their physical properties when subjected to high-speed spinning.
- The principle of centrifugation relies on sedimentation, where particles separate based on their density when subjected to centrifugal force.
- The separation efficiency depends on particle characteristics (density, size, shape), medium viscosity, and centrifugation parameters (RCF/RPM).
- Following Stokes’ law, denser particles experience stronger force and sediment faster toward the bottom of the tube, while lighter particles remain near the top.
- This technique is widely used in biological research, medical diagnostics, and industrial applications. In molecular biology and biotechnology, it’s used to purify DNA, RNA, proteins, and harvest cells and cell components such as organelles. Clinical laboratories use it to separate blood components (plasma, serum, and red blood cells) for diagnostics. Industries employ centrifugation for various purposes, including vaccine production, dairy processing, and beverage clarification.
- There are three main types of centrifugation:
- Differential centrifugation: Separates particles based on size and mass through sequential spins at increasing speeds.
- Density gradient centrifugation: Uses a density medium (like sucrose or cesium chloride) to separate particles based on their buoyant density. Includes isopycnic centrifugation, where particles band at positions matching their density.
- Analytical ultracentrifugation: Uses extremely high speeds to study physical properties of small particles like viruses, ribosomes, and macromolecules, and analyze their interactions and conformational changes.
- Different types of centrifuges are available commercially. They range from basic benchtop models for general lab work to specialized ultracentrifuges capable of 100,000+ RPM for molecular separation. Microcentrifuges handle small volumes for molecular biology, while high-speed units perform cell fractionation. Refrigerated models protect temperature-sensitive samples. Modern centrifuges feature advanced rotor designs, automated controls, and enhanced safety features, with applications spanning routine laboratory work to advanced research requiring precise molecular separation.
- Centrifuge rotors primarily come in two main types: fixed-angle rotors that hold tubes at a constant angle for efficient pelleting, and swinging-bucket rotors that pivot outward during operation for density gradient separations. Specialized rotors, including vertical rotors, exist for specific applications. Rotor selection depends on sample volume, particle characteristics, and separation goals. Proper matching of rotors with adaptors and tubes, along with appropriate speed and time parameters, ensures optimal separation results and operational safety.
- Successful centrifugation relies on careful control of key parameters including speed (RPM/RCF), temperature, duration, and sample volume. Proper sample preparation is crucial, requiring balanced tube weights, appropriate buffer selection, and correct volume adjustment.
- Safety measures are essential, including ensuring even weight distribution to prevent mechanical stress, using sealed tubes for hazardous materials, avoiding overfilling, and maintaining equipment regularly. These practices protect both the samples and equipment while ensuring accurate and reproducible results.
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