Bio-Rad Rotofor® and Mini Rotofor Cells - Manual (Page 12)

2. Place the proper ion exchange membrane on the gasket by aligning the notches
in the membrane around the pins, and complete a “sandwich” with a second gasket
on top of the membrane. The cathode holds one anion exchange membrane and
the anode holds one cation exchange membrane.
Fig. 3.2. Ion exchange membrane and gasket sandwich on inner portion of electrode assembly.
3. Make sure that there is a small O-ring inset in the central shaft of the large,
outer portion of the electrode assembly and fasten the halves together with the
captive, threaded sleeve.
4. Repeat the assembly process for the second electrode.
5. Fill the electrode chambers with electrolytes immediately after assembly to prevent
the membranes from drying. Filling is most easily accomplished with the assembled
focusing chamber mounted on its stand. The anode (+) electrode assembly (red
button), containing the cation exchange membrane, is filled with acidic electrolyte,
usually 0.1 M H
3
PO
4
. The cathode (–) electrode assembly (black button), containing
the anion exchange membrane, is filled with basic electrolyte, usually 0.1 M
NaOH. To fill the compartments, remove the vent buttons, add 25–30 ml of the
appropriate electrolyte to each chamber, so that the chambers are about 65% full,
and replace the buttons. The electrolyte should just barely cover the central shaft
of the chamber. Excessive electrolyte does not provide sufficient air space to allow
gases to escape. Pressure may build up inside the electrode assembly and cause
leaking from the vent buttons or ion exchange membranes.
The vent buttons are interchangeable and can be used with either electrode
assembly. The life of these buttons is usually 4–5 runs. After 4–5 runs, electrolyte
may begin to leak from the vent buttons during the run. If a vent button is
inadvertently perforated or, if during focusing an inordinate amount of electrolyte
leaks from the filling port, stop the run and replace the vent cap.
When the cell is used for the first time, the electrode assemblies will contain fresh
electrolyte. If the cell has been run previously, the distilled water or electrolyte
solutions must be left in the electrode assemblies between runs to maintain
hydration of the ion exchange membranes. Use fresh electrolytes for each run. If
the membranes are allowed to dry, they must be replaced. Empty the electrode
assemblies and fill with fresh electrolyte solution before each focusing run.
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