98 Agilent 7100 Capillary Electrophoresis System User Manual
5 Using the Agilent 7100 Capillary Electrophoresis System
Capillary Electrophoresis, CE
High Voltage System
The following parameters for the power supply can be controlled using the CE
Method Setup screen in the Agilent ChemStation software:
• Enable High Voltage
• Voltage
• Current
• Power
In addition you can set a Lower Alarm Limit for Current.
Positive voltage settings will configure the electrode at the inlet vial with
positive values (positive polarity). Positive polarity is regarded as the standard
setting.
You can reverse the polarity to negative by entering negative values for high
voltage. This means that a negative voltage is applied at the inlet electrode.
The outlet electrode is always grounded to ensure that the potential at the
point of detection is close to ground. Even with negative polarity, the inlet
electrode is the point where the voltage is applied and the outlet electrode is
close to ground.
Although the outlet electrode is always at the ground potential, you should
make sure that the electrode is not short-circuited to ground. The electrode is
connected to the power supply to measure the current flowing through the
capillary. If the ground electrode is short-circuited to ground, all current
flowing through the capillary is signaled as leakage current.
In order to directly apply HV from the dialog associated with the HV icon (a battery) in the
CE dashboard, the active instrument method must have Enable High Voltage check
marked.
The maximum stored energy in the CE power-supply is below 200 mJ at 30 kV. Due to this
and the fixed current limit of 300 µA the high voltage applied is not defined as hazardous
voltage.
It is good CE practice to ramp up voltage instead of switching voltage suddenly to high
values. This is regarded as gentle treatment for samples which might otherwise be affected
by the field strength, such as proteins. A linear voltage ramp from 0 to 30 kV can be
programed by starting with 0 kV and setting the voltage in the timetable to for example
0.2 minute.
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