Bio-Rad CHEF-DR® III Variable Angle System - Manual (Page 7)

Figure 1.1. Voltage clamping by the CHEF-DR III system. A. Relative electrode potentials when the
+ 60° field vector is activated. B. Relative electrode potentials when the - 60° field vector is activated.
Electrophoresis Chamber
The CHEF-DR III electrophoresis cell consists of a 44.2 x 50.3cm (17.4" x 19.8") acrylic
box with 24 horizontal electrodes arranged in a hexagon. Gels are electrophoresed horizontal-
ly, submerged under recirculated buffer. A 14 x 13 cm (5.5" x 5") gel is cast on a platform in a
separate casting stand, removed, and placed in the center of the hexagon. The platform is held
in place by a frame positioned on the chamber floor. A combination wide/long format is avail-
able as an accessory. DNA migration and buffer flow is in the direction of the arrow on the lid.
The heavy duty 0.02" diameter platinum wire electrodes, replaceable for easy mainte-
nance (see Section 6), are individually connected to the 24 pin computer cable,which con-
nects to the power module. They are each sealed with an O-ring and silicone sealant to provide
double protection against leakage. The electrodes will wear out more rapidly when switch
times below 1 second are used, and/or when 9 V/cm gradients are employed.
The two small chambers below the level of the main chamber floor at the front and rear
of the main chamber are used for buffer circulation and priming the pump. Buffer enters the
main chamber through six holes in the floor near the top. A flow baffle just in front of the
holes prevents gel movement. Buffer exits the chamber at the front through the two ports.
The right is for draining, the left for circulation. The base of the chamber has four leveling
screws for even gel submersion in buffer.
The hinged lid contains a safety interlock. The voltage passes directly from the Power
Module through a short-path in the lid interlock. If the lid is opened, the current flow is broken
and voltage to the gel chamber is disrupted. The cell also includes an internal temperature probe,
which monitors buffer temperature in the chamber and regulates cooling by the Cooling Module.
Pump and Accessories
Each system includes a variable speed pump, which provides a suitable flow rate of buffer
through the chamber. Substitution of other pumps could pose a safety hazard and cause
improper flow, and therefore lower resolution. The pump’s power supply is electrically iso-
lated within the power module for safety. Its voltage requirement is independent of the line
voltage supplied to the drive module (e.g. 100, 120, 220, or 240 volts). This pump should not
be plugged into any equipment other than the CHEF-DR III power module.
The pump is connected to Tygon ® or plastic tubing. This tubing circulates buffer in and
out of the chamber. The tubing may also pass through a water chiller. In this case, the pump
should be placed after the chiller, so that buffer flows through the chiller and then to the pump.
Typically, the dial is set at 70, for about 0.75 L/min.
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