Centrifuges
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Objective
Centrifugation is used to separate immiscible liquids and
solids from liquids. The separation is carried out by the
application of centrifugal force.
Definition
• A laboratory centrifuge is a piece of laboratory
equipment , driven by a motor which spins liquid
samples at high speed.
• Centrifuges are used in
– chemistry, biology, and biochemistry for isolating and
separating suspensions.
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MLI-mde 210, 311
Operation
•
•
separation of particles
from a solution
two fractions are
formed:
1. sediment
(pellet, solid phase)
2. supernatant
(liquid phase)
The figure was found at http://www.steve.gb.com/science/molecular_biology_methods.html (Feb 2008)
Centrifugation
separation of particles from a solution according to
their size, shape, density, viscosity of the medium
and rotor speed.
The rate of centrifugation is specified by the
acceleration applied to the sample, typically
measured in revolutions per minute (RPM) or
relative centrifugal force (RCF).
Rotor
Generally spoken, there
are two main types of
rotors:
• Fixed-angle rotor
• Swing-out rotor (=
horizontal rotor)
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MLI-mde 210, 311
Design Rotor objectives
• The rotor is closed by a rotor lid.
• The rotor is located in a rotor chamber
which is covered by a metal centrifuge
lid.
• During the run, the lid is locked.
• The lid protects the user from being
injured by touching a rapidly spinning
rotor.
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MLI-mde 210, 311
Centrifuge tubes
• Centrifuge tubes or centrifuge tips are tapered tubes
of various sizes made of glass or plastic.
• The most commonly encountered tubes are of about
the size and shape of a normal test tube (~ 10 cm
long).
• Micro-centrifuges typically accommodate microcentrifuge tubes with capacities from 250 μl to 2.0
ml These are exclusively made of plastic.
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MLI-mde 210, 311
Centrifuge tubes
Three microcentrifuge tubes: 2 mL, 1.5 mL and 200 μL (for PCR).
Four screw-top micro-centrifuge tubes.
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MLI-mde 210, 311
Types of centrifuge
There are at least five types of centrifuge:
• preparative centrifuge
• analytical centrifuge
• angle fixed centrifuge
• swing head centrifuge
• haematocrit centrifuge
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MLI-mde 210, 311
Safety aspects
• The load in a laboratory centrifuge must be carefully
balanced. Small differences in mass of the load can
result in a large force imbalance when the rotor is at
high speed. This force imbalance strains the spindle
and may result in damage to centrifuge or personal
injury. Some centrifuges have an automatic rotor
imbalance detection.
• Before starting a centrifuge, an accurate check of the
rotor lockage as well as the lid lockage is mandatory.
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MLI-mde 210, 311
Safety aspects
• Centrifuge rotors should never be touched
while moving, because a spinning rotor can
cause serious injury.
– Modern centrifuges generally have features that
prevent accidental contact with a moving rotor as
the main lid is locked during the run.
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MLI-mde 210, 311
The figures were found at
http://www.chem.arizona.edu/tpp/chemt/CAn/Graphics/centrifuge/blood%20centrifugation.png and
http://www.academic.marist.edu/~jzmz/HematologyI/Intro3.html (Feb 2008)