Working principle and application examples of centrifuge

Introduction: Centrifuge - the invisible "separating hand"

Laboratory centrifuges are indispensable equipment in biology, chemistry, medicine and other fields. They quickly separate components with different densities in liquids through centrifugal force generated by high-speed rotation. Whether it is blood stratification, cell organelle extraction, or nanomaterial purification, centrifuges play a key role. This article will analyze its working principle and typical application scenarios through a combination of graphics and text.

Working principle of centrifuges: How does centrifugal force "layer" substances?

1. The nature of centrifugal force

Centrifugal force is an inertial force that generates a "virtual force" that drives the object away from the center of rotation as it rotates around its axis. The formula is:

F = m × ω² × r
(m: mass of object; ω: angular velocity; r: radius of rotation)

2. Workflow

1. Load the sample into a centrifuge tube and place it symmetrically in the rotor (ensure balance);
2. Set the speed (RPM) and time to start centrifugation;
3. Under high-speed rotation, the denser components settle outward to form precipitates; the denser ones remain in the upper layer;
4. After stopping, the liquid is layered according to a density gradient and can be absorbed layer by layer.

• Rotor: The core component carrying the centrifuge tube (angular rotor/horizontal rotor);
• Drive motor: provides rotary power;
• Refrigeration system (optional): prevents samples from overheating;
• Control system: Adjust speed, time and temperature.

Classification and core parameters of centrifuges

1. Classification by speed

2. Analysis of key parameters

Relative centrifugal force (RCF): An indicator of actual separation efficiency, formula:

RCF = 1.118 × 10⁻⁵ × r × (RPM)²
(r: radius of rotation, unit of centimeter)

Temperature control range: -20℃ to 40℃ to protect heat-sensitive samples;
Rotor capacity: From a small amount of 0.2mL to a large amount of 1L, it can be adapted to different needs.

Classic application examples

Example 1: Blood stratification (medical testing)

Objective: Isolate plasma, white blood cells and red blood cells.

1. Collect whole blood samples and add anticoagulant;
2. Centrifuge at 3000 RPM for 10 minutes;
3. Stratified results (top to bottom): plasma (55%), white blood cells/platelets (<1%), red blood cells (45%).

Example 2: Isolation of organelles (biological research)

Goal: Extract mitochondria or cell nuclei.

1. After cell lysis, homogenate was centrifuged at low speed (1000 RPM) to remove undisrupted cells;
2. Supernatant was centrifuged at 10,000 RPM to precipitate mitochondria;
3. The final supernatant was ultracentrifuged (100,000 RPM) to obtain microsomes.

Key: Purity is improved by gradient centrifugation (e.g., sucrose density gradient).

Example 3: DNA extraction (molecular biology)

Objective: Isolate and purify DNA from cells.

1. Lysing cells to release DNA;
2. Add binding buffer and centrifuge at high speed to adsorb DNA to the silica gel membrane;
3. Washing to remove impurities;
4. DNA was eluted by low-speed centrifugation.

DNA centrifugal purification process

Example 4: Purification of nanomaterials (Materials Science)

Objective: To separate gold nanoparticles of different particle sizes.

1. The synthesized mixture is centrifuged at gradient speed:
2. 5000 RPM removes large particle aggregates;
3. Collect the target particle size (e.g., 20nm) at 15,000 RPM;
4. 20,000 RPM captures smaller particles (5nm).

Transmission electron microscopy (TEM) verified the particle size distribution.

Operational precautions

• Balancing and symmetry: Centrifuge tubes need to be placed symmetrically, with a quality difference of ≤0.1g to avoid accidents caused by rotor imbalance;
• Speed limit: It is strictly prohibited to exceed the rated speed of the rotor;
• Biosafety: Pathogen samples require the use of sealed rotors or biosafety centrifuges;
• Maintenance: Regularly clean up rotor corrosion and check for aging of seal rings.

Future outlook: intelligence and miniaturization

• Intelligent centrifuge: Built-in sensors monitor centrifugal force and temperature in real time and automatically adjust parameters;
• Handheld centrifuge: USB-powered micro device to meet the needs of rapid on-site testing;
• Green design: Low-noise, low-energy rotors have become mainstream.

Centrifuges achieve efficient separation of complex mixed systems through simple physical principles. From medical diagnosis to cutting-edge scientific research, it continues to push the boundaries of scientific development. Understanding its principles and standardizing operations are essential skills for every experimenter.