Baseline decreasing with temperature program

[Rui]

Hi there

I need a help please.

I am working with GC-FID Focus GC ThermoFinnigan, a GC column DB5-MS from Varian, with the following gradient temperature program:

0-2 min 40 ºC
3ºC/min until 175 ºC
5ºC/min until 250 ºC
250ºC for 15 minutes

Injector 250ºC
Detector 260ºC
Split flow 1/40
He 1,5 mL/min
N2 as make-up gas

After 7 minutes of running the program the baseline drops.
I have checked possible leaks, the flow rate of the gases are stable, the setpum is new and I think the column conditions are appropriated.

Can you help me with this problem?
Can I quantify the peaks even with this drift?

Thank you in advance

Best regards

Rui

[larkl]

is it a gradual decline? Lots of runs will show some baseline drift. You'll just have to look at the integration and see if the drift looks detrimental to the results.

[JI2002]

One possibility is that you are running column compensation. If the baseline profile changes, you could have a baseline drifting lower. If that's the case, you may need to rerun the column compensation.

[JTM]

Maybe a good cleaning of the column?

I still want to say it's a leak. You're absolutely positive there are none? Typically the baseline goes up with temperature though... so it may not be.

[Rui]

Thank you all for your help

is it a gradual decline? Lots of runs will show some baseline drift. You'll just have to look at the integration and see if the drift looks detrimental to the results.

We only made a few runs, the decline apear all the time, don´t increase with the number of runs.

I will se again if I have any leak.
Could be also the fact that the column don´t reach the detector?