Bio-Rad Criterion™ Blotter - Manual (Page 10)

2. Current limits
The PowerPac 200 Power Supply is capable of a 200 watt output. Unless a current limit
is set, uncontrolled conductivity changes may result in full power being delivered to the
Criterion Blotter cell. The gel holder and electrode cards may warp, and the transfer buffer
may heat up (further increasing conductivity). This would result in a potential safety
hazard. Refer to the PowerPac 200 Power Supply Instruction Manual for procedures to set
current limits and run times.
3. Polarity of transfer
Do not reverse polarity with the plate electrodes. This will result in corrosion and rusting
of the stainless steel cathode. If this should occur, the stainless steel should be cleaned with
a mild abrasive cleanser to remove the rust. Damage to electrode plates is not covered
under warranty.
4. Heat dissipation
Two methods of heat dissipation are available. The efficient transfer and high intensity
field of the Criterion Blotter requires some method of heat dissipation. The sealed ice
block cooling system is adequate for transfers of less than 1 hour where slightly elevated
temperatures at the end of the transfer are acceptable. Where precise temperature control
is required or transfers runs longer than 1 hour at high voltage conditions, the optional
cooling coil connected to a refrigerated recirculating bath should be used. Placing the
Criterion Blotter cell in the cold room is an inadequate means of controlling transfer
buffer temperature. The tank of the Criterion Blotter cell is an effective thermal insulator,
thus limiting the efficient dissipation of heat.
6. Use of a stir bar during transfer
For all blotting applications a stir bar must be placed inside the Criterion Blotter cell so
that the transfer buffer is stirred during the course of the experiment. This will help to
maintain uniform conductivity and temperature distribution during electrophoretic
transfer. Use of a stir bar prevents the appearance of tiny bubbles on blots as well.
7. Transfer buffer pH
Do not adjust the pH of transfer buffers unless specifically indicated. Adjustments of the
pH of transfer buffers, when not indicated, will result in increased buffer conductivity. This
is manifested by a higher than expected initial current output, possible heating problems,
and a decreased resistance.
8. Transfer buffer recommendations
Use only high quality, reagent grade methanol. Contaminated methanol can result in
increased transfer buffer conductivity, as well as poor transfer of macromolecules. Reuse
of transfer buffers is not advised, since these buffers have most likely lost their ability to
maintain a stable solution pH during transfer. Dilution of transfer buffers below their
recommended levels is also not advised, since this will decrease their buffering capacity.
9. Voltage limits
Do not increase voltage settings beyond those indicated in Tables 3.1–3.4 for overnight
operation. Initial current readings must be close to the current listed and a current limit
should be set on the power supply. If overnight transfers at low voltages are ineffective
for your application, and higher voltages are necessary, transfer times must also be adjusted
to a shorter length. Failure to do so may result in a potential safety hazard.
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