Centrifuge – principle & types (Lecture for 7th semester)

Centrifuge – principle & types (Lecture for 7th semester)

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  Centrifuge – principle& types Dr Showkat Ahmad Wani
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  Introduction • Have youever seen how cream separates from milk? Or how washing machines remove water from clothes after rinsing? • That’s centrifugation in everyday life! • In biology and chemistry laboratories, centrifuges are used to separate particles—like cells, organelles, or proteins—from a liquid based on their size, shape, and density.
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  What is aCentrifuge? • A centrifuge is a machine that spins samples at very high speeds, causing particles in a liquid to experience a centrifugal force that separates them according to their density. • The heavier particles move outward (toward the bottom) of the tube, forming a pellet, while the lighter particles remain in the liquid above, called the supernatant.
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  Principle of Centrifugati on • Theprinciple is based on the centrifugal force generated when an object moves in a circular path. • When a mixture is rotated at high speed: • Each particle experiences an outward force (centrifugal force). • The rate of sedimentation depends on: • The mass and shape of the particle, • The density of the medium, • The rotational speed (rpm or revolutions per minute). • Mathematically, Where: • F = centrifugal force, • m = mass of particle, • ω = angular velocity, • r = distance from the center of rotation.
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  Key Terms • Sedimentation:The settling of particles under centrifugal force. • Pellet: The solid part that collects at the bottom of the tube. • Supernatant: The liquid layer above the pellet. • Rotor: The rotating part of a centrifuge that holds the tubes.
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  Types of Centrifuges •Let’s classify centrifuges based on speed and purpose:
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  Clinical Centrifuge (Low-SpeedCentrifuge) 1️ 1️ ⃣ • Speed: Up to 4,000–6,000 rpm. • Used for: Routine separation of blood components (e.g., serum, plasma, red cells). • Rotor type: Usually fixed-angle or swing- bucket. • Example: Blood testing in diagnostic labs.
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  High-Speed Centrifuge 2️ 2️ ⃣ • Speed:10,000–25,000 rpm. • Used for: Separating cell organelles, precipitated proteins, etc. • Requires cooling to avoid heat damage to biological samples. • Example: Separation of mitochondria, nuclei, or cell debris.
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  Ultracentrifuge 3️ 3️ ⃣ • Speed: 60,000–150,000rpm (very high). • Used for: Separation of macromolecules like DNA, RNA, ribosomes, and viruses. • Principle: Generates forces over 500,000 × g (times the earth’s gravity!). • Requires vacuum to prevent air resistance and heat buildup. • Example: Used in molecular biology and virology labs.
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  Refrigerated Centrifuge 4️ 4️ ⃣ • Hastemperature control (0–4°C) • Used for: Heat-sensitive biological samples (e.g., enzymes, cells, proteins). • Can be low-speed or high-speed type with cooling.
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  Microcentrifuge 5️ ⃣ • Used forsmall volumes (0.5–2 mL) in microtubes. • Speed: Up to 15,000 rpm. • Common in molecular biology for DNA extraction, RNA purification, etc.
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  Differential vs DensityGradient 6️ 6️ ⃣ Centrifugation (Advanced Types) Type Basis of Separation Example Differential centrifugation Based on size & density – larger particles sediment first Separation of cell organelles Density gradient centrifugation Based on buoyant density in a density medium like sucrose or CsCl Separation of DNA or viruses
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  Applications of Centrifugation •Clinical labs – Separate blood into plasma and cells. • Biochemical research – Isolate proteins, enzymes, or organelles. • Microbiology – Harvest cells from cultures. • Molecular biology – Purify DNA, RNA, or viruses. • Industry – Clarify fruit juices, purify vaccines, and wastewater treatment.
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  Precautions • Always balancethe tubes properly before starting. • Never open the lid while the rotor is moving. • Use sealed rotors for infectious materials. • Maintain temperature control for biological samples.
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  📋 Summary Term Meaning Principle Separationbased on centrifugal force due to differences in density and size Pellet Heavier particles collected at the bottom Supernatant Liquid above the pellet Types Clinical, High-speed, Ultracentrifuge, Microcentrifuge, Refrigerated Applications Medical, research, industrial separations
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  Thank you