Overview
The lecture introduces the basic principles, setup, and common applications of centrifugation in biological research, including sample collection and particle separation.
Principles of Centrifugation
- Centrifugation involves rotation around a single axis, generating outward rotational force.
- The centrifugal force pushes materials to the end of the tube, aiding in separation or collection.
- It is used in biology to collect samples or separate particles within a mixture.
Centrifuge Operation and Settings
- Tabletop centrifuges have an "Open" button to access the sample compartments.
- Main settings to control are time (duration of spin) and speed.
- Speed can be set in RPM (revolutions per minute) or RCF (relative centrifugal force).
- RPM counts how many complete circles the centrifuge makes per minute.
- RCF standardizes force between different centrifuges by relating speed to gravity (g).
Balancing and Running a Centrifuge
- Samples should be loaded in a balanced manner around the rotor’s circle.
- If using a single sample tube, balance it with another tube containing an equal volume of water.
- Secure the lid tightly to prevent leaks before starting the run.
Applications: Sample Collection and Separation
- Centrifugation collects dispersed samples at the tube’s bottom for small volumes.
- For particle separation, centrifugation pellets heavier particles (like bacterial cells) at the tube bottom.
- The remaining liquid (supernatant) can be carefully removed with a pipette, leaving the pellet undisturbed.
Key Terms & Definitions
- Centrifugation — Separation process using rotational force to separate components by density.
- RPM (Revolutions Per Minute) — Number of full spins the centrifuge rotor makes in a minute.
- RCF (Relative Centrifugal Force) — Centrifugal force relative to gravity, standardizes between machines.
- Supernatant — The clear liquid above the solid pellet after centrifugation.
- Pellet — The compacted solid particles collected at the tube's bottom after centrifugation.
Action Items / Next Steps
- Practice loading and balancing samples in a tabletop centrifuge.
- Review the settings and units (RPM vs RCF) before any experiment.
- Ensure careful pipetting when removing supernatant to avoid disturbing pellets.