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Selecting CsCl Gradients
Rotor speed is used to control the slope of a CsCl density gradient, and must be limited to prevent
CsCl precipitation during centrifugation. Speed and density combinations that intersect on or
below the curves in
that CsCl will not precipitate during centrifugation in these rotors. Curves are provided at two
temperatures: 20°C (black curves) and 4°C (gray curves). Curves in
provided up to the maximum speed of the rotor.
NOTE
The curves in
other salts are present in significant concentrations, the overall CsCl concentration may need to be
reduced.
The reference curves shown in
Each curve
Figure 5
is within the density limits allowed for the SW 32.1 Ti rotor. Each curve was generated for
a single run speed using the maximum allowable homogeneous CsCl densities (one for each fill
level) that avoid precipitation at that speed. (The gradients in
generated from step or linear gradients, or from homogeneous solutions. But the total amount of
CsCl in solution must be equivalent to a homogeneous solution corresponding to the concentrations
specified in
the banding positions of sample particles. Curves not shown may be interpolated.
Adjusting Fill Volumes
Figure 2
through
partially filled with gradient solution, float mineral oil (or some other low-density, immiscible
liquid) on top of the tube contents to fill the tube to its maximum volume. (Do not use an oil overlay
in Ultra-Clear tubes.) Note that for a given CsCl density, as the fill level decreases the maximum
allowable speed increases. Partial filling may be desirable when there is little sample or when you
wish to shorten the run time
For example, in the SW 32 Ti rotor, a quarter-filled tube of 1.69-g/mL homogeneous CsCl solution at
4°C may be centrifuged at 25,000 RPM (see
from the quarter-filled line to r
a half-filled tube may be centrifuged no faster than 17,000 RPM, and 15,000 RPM in a three-quarter-
filled tube. A tube full of the 1.69-g/mL CsCl solution may be centrifuged no faster than 13,500 RPM.
Curves not shown in the figures may be interpolated
LXL-TB-015BB
Figure 2
(for the SW 32 Ti rotor) and in
Figure 2
through
Figure 5
Figure 3
inFigure 3
is within the density limits allowed for the SW 32 Ti rotor; each curve in
Figure 3
and
Figure
5.)
Figure 3
Figure 5
show that several fill volumes are possible in a tube. If a thinwall tube is
(the tube bottom) represents this gradient. The same solution in
max
SW 32 Ti and SW 32.1 Ti Swinging-Bucket Rotors
Figure 4
are for solutions of CsCl salt dissolved in distilled water only. If
and
Figure 5
show gradient distribution at equilibrium.
Figure 3
and
Figure 5
can also be used to approximate
Figure
2). The segment of the 25,000 RPM curve
Preparation and Use
(for the SW 32.1 Ti rotor) ensure
Figure 2
through
Figure 5
and
Figure 5
can be
(Figure
are
3)
19
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