Bio-Rad Rotofor® and Mini Rotofor Cells - Manual (Page 10)

flow. The anion-exchange membrane is notched to fit only the cathode assembly (black
button) and the cation exchange membrane will fit only the anode assembly (red button).
Before the initial use, the membranes must be equilibrated overnight in the
appropriate electrolyte. Once wetted they cannot be allowed to dry. If they dry out,
membranes should be discarded. Membranes generally last 4–5 runs.
Anion Exchange Membranes are equilibrated in 0.1 M NaOH.
Cation Exchange Membranes are equilibrated in 0.1 M H
3
PO
4
.
Gaskets - Four grey colored silicone rubber gaskets are provided to seal the
ion exchange membranes within the electrode assemblies. These will fit either
electrode assembly.
Vent buttons - Both electrode assemblies have filling ports. Vent caps containing
integral, gas-permeable, PTFE membranes provide pressure relief form the gases
which build up in the electrolyte chambers during the run. The vent buttons will fit
either electrode assembly.
Housing - The stand supports the assembled focusing chamber during the run
and houses the rotation motor. Focusing power is transmitted to the focusing chamber
through brass contacts that are spring-loaded to maintain constant electrical contact
between the focusing chamber and the housing. The assembled focusing chamber
fits on the stand, with the anode (red) compartment to the left. If assembled correctly,
the cathode electrode assembly will engage with the gear on the housing. If any
connections are loose, the unit will not fit. Electrical contact to the case is through
jacks on the safety cover. The safety cover must be in place for safe operation of the
Rotofor cell.
Harvesting apparatus - A test tube rack which holds 20 test tubes (12 x 75 mm
culture tubes) is enclosed in the harvesting box. This box has a fitting for connection
to a vacuum source. House vacuum is usually sufficient for harvesting. Stainless
steel tubes on the lid of the box are connected to an array of needles by flexible
tubing. Individual fractions are collected through the tubing into the test tubes.
Cooling finger - The ceramic cooling finger extends through the focusing
chamber and the electrode assemblies. The cooling finger is in contact with the
sample and provides efficient heat dissipation up to 20 W.
Section 3
Setting Up For A Run
Assemble the anode and cathode electrolyte chambers first. Alignment pins prevent
misassembly of the two electrodes. The anion-exchange membrane is notched to fit
only the cathode compartment (black button) and the cation exchange membrane will fit
only the anode assembly (red button). The four silicone rubber gaskets can be used in
either electrode assembly. The procedure is identical for assembly of both the mini
focusing chamber and standard focusing chamber.
3.1 Equilibration of the Ion Exchange Membranes
Ion exchange membranes are used in the Rotofor cell to separate the sample
from the electrolyte while allowing current flow. The ion exchange membranes
used in the Rotofor cell are of two types: cation exchanger and anion exchanger.
The cation exchanger is negatively charged and repels negatively charged ions,
preventing them from contaminating the anolyte. The anion exchanger works in the
opposite way; it is positively charged and repels positive ions.
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