Theory of Operation
Power
Considerations
Electrophoresis is the migration of a charged particle under the influence of an
electrical field. The influence of various power supply output parameters (volts,
current and watts) is derived from two equations:
Voltage = Current x Resistance (V=IR)
Wattage = Current x Voltage (W=IV)
Resistance
Resistance of the assembled electrophoresis cell is dependent on the
conductivity of the gel buffer, the thickness of the gel, and the number of gels
being run. Although the resistance is determined by the gel system, the
resistance can vary over the course of the run. For instance, in the Tris-Glycine
buffer system, the fast moving, highly conductive chloride ions in the gel are
gradually replaced by the slower moving, less conductive glycine ions from the
running buffer as the gel runs. As a result, the resistance of the gel increases as
the chloride/glycine front moves down the gel, and the current decreases.
Voltage
The velocity in which an ion moves in an electric field will vary in proportion to
the field strength (Volts per unit distance). The higher the voltage the faster an
ion will move.
Current
Current is a function of the number of ions passing a given cross-section of the
circuit at a given time. For a given gel/buffer system, at a given temperature,
current will vary in proportion to the field strength (voltage) and/or cross-
sectional area (number and/or thickness of the gels). Ions in solution and at a
given voltage will move faster as the temperature increases, increasing current.
Power
Watts, or the rate of heat generated by the system, is a function of voltage and
current (W=IV). For a given gel system if either voltage is doubled, watts will
also double (as V=IR, and R is a “constant” determined by the gel system).
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