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4
Operation
Backflushing the Column
One useful feature available with EPC control of the makeup is the ability to
backflush unwanted higher boiling analytes from the column. Use of this
feature requires that the split/splitless inlet be used. Backflushing reduces the
hold at the end of the run to clean out the column.
To backflush after elution of the last peak of interest, the MSD is
time-programmed to stop collecting data, the splitter makeup pressure is
time-programmed to rise rapidly, and the inlet pressure is reduced rapidly.
These pressure changes reverse the flow through the column. Heavy materials
are then carried out the split vent of the inlet.
The inlet pressure is programmed to decrease to 0.5 psig. The makeup
pressure is programmed to rise to a maximum pressure determined by the
detectors and cleanout temperature used.
Using the example above, the MSD will limit the flow, and thus pressure, that
can be used for backflushing. The flow allowed to go to the MSD should be no
more than 25 mL/min with a standard turbo and 100 mL/min with the
performance turbo. Diffusion pumps cannot be used with backflushing. The
backflushing conditions must be calculated to not exceed this.
Make sure that MSD acquisition is OFF while backflushing to prevent possible damage
C A U T I O N
to the ion source.
We need to use the MSD restrictor tubing dimensions and the backflushing
temperature to find the backflushing pressure. For this example, we will use
20 mL/min going to the MSD.
48
Installation and Operation Guide
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