Chromatography Forum

If the auxiliary EPC channel controls the column head pressure and therefore must be greater than Inj B pressure at all times, but it drops quickly to its initial value at the end of the temperature program (this is set according to the manual), then how can the EPC channel be programmed for a sequence of runs and therefore repeated cooling downs during which Inj B pressure decreases slowly?

We have similar 5890 II with EPC, but not on a GCMS (you posted in that section).

Ours uses Aux flow to control the total carrier gas plus split flow. When the Run is completed, it will go back to the Method Initial values, and when ready, the next injection begins. Is that what you're asking, confused here.

What is the pressure of your cylinder regulator? What is the aux EPC pressure and what are your column, split, and purge flows? My aux EPC pressure doesn't change during runs.

Yes, I posted in the GCMS section, we have the HP 5890 with an MSD. Our problem is that the aux EPC does not change as the column head pressure does, it can be programmed to increase during the run at whatever rate we want but we have no control on the cooling down part and when the run is finished, the aux EPC returns to its initial value but VERY fast, almost immediately and thus it reaches the column head pressure (which is decreasing much slower as temperature decreases) in seconds and then is when the instrument starts beeping because aux EPC has to be higher than the column head pressure, this is specified in the manual for gas saver configuration (one of the uses of the aux EPC).

I was not around when the instrument was installed but it seems configured for gas saver.

We have similar 5890 II with EPC, but not on a GCMS (you posted in that section).

Ours uses Aux flow to control the total carrier gas plus split flow. When the Run is completed, it will go back to the Method Initial values, and when ready, the next injection begins. Is that what you're asking, confused here.

cylinder P is about 70 bar, the rest can be set at whatever pressure we want/need. Also aux EPC P can be set to constant or variable during runs. Example, at initial temp 50C, aux EPC E set to 50 kpa, Inj B to 35 or around, column flow 1.5 ml/min, splitless, purge is set to around 2.6 ml/min. Running at constant flow, inj B will be about 110 kpa at 320C and aux EPC can be set to increase to whatever as long as it is higher than that, eg. 140 kpa, however it can be set to go up to 400 kpa at the top of the temp program if we like. The problem is the cooling down part as the aux EPC pressure channel does not use the pressure vs flow calculations that the inlet channel have. This last sentence is as stated in the manual.

What is the pressure of your cylinder regulator? What is the aux EPC pressure and what are your column, split, and purge flows? My aux EPC pressure doesn't change during runs.