Bio-Rad Rotofor® and Mini Rotofor Cells - Manual (Page 11)

Using the ion exchange membranes gives a concentration gradient of the
corresponding ions at the respective ends of the sample chamber. The highest
concentration of negative ions will be next to the cation exchanger and the highest
concentration of positive ions will be next to the anion exchanger.
Prior to assembly, the ion exchange membranes must be equilibrated
overnight in the appropriate electrolyte solution. Ion exchange membranes are
used for 4–5 runs prior to replacement.
Anion Exchange Membranes: These membranes are lighter in color than the
cation exchange membranes when dry. The color of the two membranes is similar
when wet. These membranes are equilibrated in 0.1 M NaOH. They are stored in
distilled water or electrolyte between runs.
Cation Exchange Membranes: These membranes are darker colored than
the anion exchange membranes when dry. These membranes are equilibrated in
0.1 M H
3
PO
4
. They are stored in distilled water or electrolyte between runs.
Note: The membranes can be stored indefinitely when dry. After rehydration, they
must be kept moist. If the membranes dry out, they should be discarded.
3.2 Assemble the Electrodes
1. Examine the inner portion of an electrode assembly. For the Standard Rotofor
there should be a small O-ring in the central hole on the flat side, and a large
O-ring seated in the large groove around the central shaft on the other side. For
the mini chamber, the outer portion contains only one large O-ring. Place a gasket
over the alignment pins and seat it on the flat surface of the inner assembly. The
three oblong holes in the ion-exchange gaskets should align with the six holes
of the electrolyte chamber. When properly aligned, the gasket should not
obstruct the six holes in any way.
Fig. 3.1. Outer and inner portions of the electrode assemblies. Arrows indicate O-rings. Electrolyte
buffer should just cover the central shaft when completely assembled. For the mini focusing chambers,
the six holes in the inner portion of each electrode assembly are much smaller in diameter than six
holes in the inner portion of the electrode assemblies used with the larger focusing chamber. In addition
the six holes for the mini chamber are drilled at a distinct angle to the central axis of the assembly.
These parts are not interchangeable!
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Central shaft
Large o-ring
Inner portion
Outer portion