GC-FID baseline falls as temp increases, then rises

[hellovorld]

Hello all

I am having the following issue. At isothermal step, the baseline is level. When the ramp step begins, the baseline falls as seen in the picture.

I have reinstalled column and changed liner o-ring and septum. The problem persists after changing these. Any suggestions is appreciated. Many thanks!

[dblux_]

... Any suggestions is appreciated. Many thanks!

How the chromatogram looks like when you change to constant flow mode ?

Much more information needed including column and program details.

[hellovorld]

OV-1701, 25 m, 0.32 mm ID, 2.0 um film

init: 50C, hold 1 min
ramp: 20C/min to 200C, hold for 10.5 min

This is constant pressure mode. I will run constant flow and report results.

[dblux_]

...
This is constant pressure mode. I will run constant flow and report results.

So it was right guess.
When you change to constant flow your baseline won't drop, but will rise.

Quite simple explanation of baseline drop. When temperature rises in constant pressure mode flow drops accordingly and FID signal as well.

BTW - what is initial pressure in 50 degC ?

[hellovorld]

Constant flow mode has corrected the issue.

Thanks for the help.

Initial pressure was 10 psi. I was using method from a similar site. This makes me wonder about the original user's results.

Thank you again!

[dblux_]

Hello world !

My pleasure