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Operation 4
Installation and Operation Guide 47
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, the splitter makeup pressure is time-programmed to rise rapidly
after elution of the last peak of interest while the inlet pressure decreases
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 from above, the
MSD will limit the flow, and thus pressure, that can be used for backflushing.
The flow allowed to go to the MSD (with a performance turbo) must be
8 mL/min or less. The backflushing conditions must be calculated to not
exceed this. We need to use the MSD restrictor tubing dimensions and the
backflushing temperature to find the backflushing pressure.