User guide

Columns and Oven 9
Advanced User Guide 293
1
Verify that all columns are properly configured.
2 Enter all method parameters for the analysis: sampler
parameters, inlet parameters, oven temperature profile,
detector flows and temperatures, and so forth.
3 Program the oven for the backflush.
• Include any temperature profile needed for backflush.
• Set the total run time to include sufficient time for
backflush.
4 Program the flow ramp for the column installed between the
inlet and the CFT device. After the last analyte elutes or
after reaching the last temperature of interest, program a
fast ramp with a final flow that is negative.
5 Program the flow ramp for the primary column installed
between the CFT device and the detector. Typically hold at
the method’s final value for the backflush duration.
If you turned off data acquisition in a data system during
backflush, remember to turn it on again at the end of the run.
Backflushing using a switching valve
Backflushing is done using a column switching valve controlled
by the Run Table. See “Run Time Programming” on page 14.
The valve is plumbed as follows:
• Position 1 Carrier gas flows through the column to the
detector. This is the normal flow path.
• Position 2 Carrier gas flows through the column toward the
inlet, removing components on the column through the inlet
vent line.
The Run Table contains commands to perform these actions:
• After the last peak of interest appears, switch the valve to
Position 2. Higher boiling peaks are discarded through the
inlet vent.
• At the same time, turn data acquisition off.
CAUTION
To avoid damage to an MSD, Agilent strongly recommends setting
up backflush as a post run event, not as part of a ramped column
program. If you still choose to backflush as part of a run, be very
careful that the flow into the MSD does not exceed the limits of the
vacuum pump.