W6 - Centrifugation Flashcards
Define sedimentation
The tendency for the particles which are in suspension to settle out of the fluid content.
deposited/settling
depends on: particle density (rho, ρ) relative to the medium, and radius, and the viscosity of the medium (eta, η)
How does sedimentation occur?
Because of their own motion through the fluid in response to all the forces that are acting on them.
The forces can be because of the gravitational pull or due to the centrifugal caused by acceleration.
Define centrifugal
The outward or outwardly directed force experienced by an object or particle moving in a circular path.
tending to move away from a centre
What is the Relative Centrifugal Forces (RCF)?
(on earth)
Measured relative to the earth’s gravitational field.
g = 981 cm s^-2
9.81
What is Applied centrifugal force (G)?
G = ω^2 r
ω = angular velocity (radians sec^-1)
r = radial distance of the particle
from the axis of rotation (cm)
How is g converted to rpm and then to radius?
How do we state the methods in primary literature?
example: “the sample was spun at 25,000 rpm”
Example: the sample was spun at 5000 x g
What are the 2 types of centrifuge?
- preparative
- analytical
differ in:
* max speed
* precense/absence of vacuum
* temp control
* sample volume
What are the types of preparative centrifuge?
- Benchtop microfuge – small Vs up to ~10,000 g
- Larger benchtop centrifuge – larger Vs up to ~ 7,000 g
- High-speed centrifuge – up to 100,000 g
- Ultracentrifuge – up to 600,000 g
benchtop is what we use in practicals
How does analytical ultra-centrifugation work?
Measure either
* absorbance
* refraction (if concentration changes, so does refractive index
What are the 3 types of rotors?
- fixed-angle
- vertical-tube
- swinging-bucket
What is the effect of a fixed-angle rotor on sample separation?
od
What is the effect of a vertical tube rotor on sample separation?
What is the effect of a swinging-bucket rotor on sample separation?
