Agilent Technologies 7100 User Manual page 99

Using the Agilent 7100 Capillary Electrophoresis System 5
Capillary Electrophoresis, CE
Voltage, Current and Power
Voltage, current and power are related to each other by the resistance of your
capillary/buffer system. You can set values for each of these three parameters.
The individual values are treated as limits. The limit that is reached first
applies. You can only enter absolute values for current and power.
If you only want to control the voltage and not the current and power, you can
set those two to the system limit (typically: 300 µA, 6 W) and the system will
permit the maximum value.
Lower Alarm Limit for Current
When using constant voltage mode, the current is normally the indicator of the
stability of the system. A rapid current decrease or drop can indicate
instability in the system. By setting a lower alarm limit you can define when
you want to be warned of such instable conditions during the run.
Instable conditions can be caused by:
• No buffer in the capillary
• Air bubble in the capillary
• Clogged capillary
• Broken capillary
Current values are dependent on the buffer concentration, the type of buffer
used, the inner diameter and length of the capillary, and the temperature.
When running the Example Method for the Test Sample (see "Setting Up a Test
Sample Run" on page 252) normal current values are below 50 µA.
If you set the lower alarm limit and the it is not exceeded 30 seconds after
start of the run, the run is stopped. When the lower alarm limit is reached
during the run part of the analysis (when the HV is applied), your current run
is stopped. During a sequence the system continues with the next analysis.
Do not use the lower alarm limit or program the time if changing the inlet or
outlet vial during the run (for example for fraction collection). Otherwise, the
system will stop when changing the vial because the lower alarm limit is
reached.
Agilent 7100 Capillary Electrophoresis System User Manual 99