Split flow set point issues

[Rhodium]

Comrades,

I am experiencing issues on an Agilent 7890 GC-FID and hoped for some insight before digging into the split vent line and trap.

Conditions:
split/splitless inlet running in split mode
column flow 4 ml/min
split ratio 5
split flow 20 ml/min
total flow 27 ml/min


When the method is initialized or "set up" in Empower and the instrument tries to go to the set points, in order to reach the 20 ml/min split flow set point, the column flow jumps to around 8 ml/min. If the column flow is manually set to the correct 4 ml/min column flow on the GC keypad, it drops the split flow to 6 ml/min.

No leaks could be identified using electronic leak detector. I have narrowed down the issue in my mind to restriction in the split vent line or restriction in the split trap, but I wanted to get some input before I changed these out because they are a pain in the *ss to get to. I am hoping something more sinister isn't at work here like a malfunctioning EPC.

Any recommendations appreciated as always.

Regards,

Mike

[dvdthomas345]

Hi, Did u mention the dimension of the column in the GC method preparation.....???

[Rhodium]

Oops - 15 m column .53 id ; column length verified on GC keypad

[AaronAIT]

Have you checked the flow at the split vent to verify that it is at 20ml/min when you set the flows manually from the GC keypad?

[Peter Apps]

Are you selecting constant pressure or constant flow ?

When the column flow is 4 ml/min, what is the inlet pressure ?

Have you measured the column flow with a flow meter or dead time, or are you trusting the GC readout ?

Check that you have selected the right carrier gas.

Perter

[dlbenach]

I would check my column configuration on the GC panel and make sure col 1 and col 2 are not configured for the same inj or det. I have had similar problems when both col 1 and col 2 were configured for the same inj or det. I have only had this problem with the 7890 and Empower 2 and 3 not for the 6890.

ps I thought I posted this reply yesterday but don't see it. If it's a duplicate I apologize.