Using an AUX EPC for helium pressure control at the inlet of a Markes Thermal Desorption unit

Hello everybody,

Our GC-MS has two setups:

- classic: GC injector - column - MSD,

- less classic: thermal desorption (TD) unit - transfer line until GC oven - ultimate union - column - MSD.

The less classic setup operates at constant helium pressure controlled though a manual valve and a gauge installed before the TD unit and after the gas filters. There is the need to swap columns between setups as they are different.

We have an unused AUX EPC installed (I think it was meant for a purged union for backflushing purpose) and I was wondering if I could connect one of the outlets of that EPC to the inlet of the TD unit to start controlling the pressure though the GC-MS software. This way I would have a better control of the method pressure and, most importantly, I could leave both columns in the oven no matter what setup I'm using (I would always control a small pressure of He in the unused column).

However, I have been told that it could not be that kind of EPC. It had to be a Split/Splitless or Multimode EPC.

Can someone explain what is the difference between those EPC's?

Thank you.


Parents Reply
  • Total flow is column flow + split vent flow + septum purge.  Less than 20 ml/total flow into the typical inlets used with capillary columns is not recommended.  It might be controlling, but at very low flows air diffuses back through the split vent and septum purge vent into the inlet, into the column, and into the MS with the source and quad hot.  It's not worth chancing oxygen damage to the column phase or contamination of the MS analyzer. 

Was this helpful?