Chromatography Forum

I found my machine in the shutdown status after running a sequence, and it would be greatly appreciated if I can receive some inputs.

The machine set up:
Agilent 6890 with Gerstel MSP2
Flip top inlet closure with General purpose Merlin microseal

After a sequence, the machine shifts from a regular testing method of 2.2 ml/min (~35 psi) to an "idle/conserve/hibernation" method of 0.5 ml/min (~7.5 psi) (no change in inlet temperature).

Before starting a sequence, I check to make sure that the machine is stable at the "idle/conserve/hibernation" parameter for at least 1 hour while I prepare the samples. However, after a sequence, I found the machine being left at the shutdown status due to pressure not being able to be achieved.

No leak is detected, so I usually remove the septum, re-install it, and that seems to work...

Is it possible that the machine is just not very stable at such low flow rate?

I am out of my wits, and it would be greatly appreciated if I can receive any inputs!

Thanks!

At low flow and low pressure it will be much more sensitive to leaks and pressure fluctuations.

Yes, it is very likely the pressure setting of the standby method can not be achieved or the GC can not maintain it.

Check the standby method if the gas saver setting is on. If on, at which flow (this should be the flow through the split vent). It's possible that the combination of this flow and the 0.5 ml/min through the column is not viable.

Is the standby method splitless? I found that, even if it's splitless, the gas saver setting put it in split after the time specified as 'gas saver time'.

Unless you have a very long narrow column setting a flow of 0.5 ml/min will lead to a negative pressure in the inlet as the MS vacuum pulls gas down the column faster than the EPC is set to deliver it. If your plan is to save gas, then do it by changing the split ratio, not the column flow.

Peter