Density centrifugation separates substances based on their density using a centrifuge. The process leverages the differences in mass and inertia of particles within a sample.
The Mechanism
Spinning a sample in a centrifuge creates centrifugal force. This force pushes denser particles—those with greater mass—further outwards, towards the bottom of the tube. Conversely, less dense particles remain closer to the top. This principle forms the basis of density centrifugation, separating components based on their buoyancy density or sedimentation rate. (Sigma Aldrich)
Different types of density centrifugation exist:
- Rate-zonal centrifugation: Separates particles based on their sedimentation rate. Particles with faster sedimentation rates reach the bottom of the tube quicker. This technique does not require equilibrium. (ScienceDirect)
- Isopycnic centrifugation (Equilibrium density gradient centrifugation): Uses a pre-formed density gradient. Particles migrate through the gradient until they reach a position where their density equals the density of the surrounding medium – their isopycnic point. This method separates particles based on density alone, regardless of size or shape. (ScienceDirect)
Practical Applications
Density centrifugation finds use in various fields:
- Biology and medicine: Separating blood cells (like leukocytes) into specific populations. (Akadem) Purification of viral vectors (e.g., isolating full AAV). (Beckman) Analyzing sperm quality. (NCBI)
- Biochemistry: Separating macromolecules based on size, shape, and density. (ASU)
- Microbiology: Isolating microalgae using density gradients. (CSIRO)
Example: Blood Separation
In blood separation, a density gradient is created using a medium like Percoll. When blood is layered on top, the denser red blood cells settle at the bottom, followed by other cell types based on their densities. The resulting distinct bands allow for easy isolation of specific blood components.
In summary, density centrifugation is a powerful technique that exploits the differences in density of particles to achieve separation, with applications spanning diverse scientific disciplines.
