Increasing FID Signal

[scnolte91]

Hello,

Analysts are running on a 7890B through a Waters LAC/E Acquisition server to Empower 3. Their FID signal has been decreasing over the past few weeks to the 1.2-1.5 range, and they're concerned about their runs being interrupted by the flame trying to reignite if their signal drops below their 1.0 lit offset.

It seems like dropping their lit offset lower would require approval for changing their method and they want to avoid that. One of the analysts says there's a way to 'bump' up the FID signal through the keypad somehow. Is anybody familiar with this?

Thanks!

[rb6banjo]

I don't know what your "rules" are as far as changing methods go but changing that Lit Offset only changes the current flow through the flame required to tell the system "yes, I'm on". It should not affect your calibrations.

Perhaps your support gases have become extraordinarly clean so the background is not has high? That's a pretty low background signal. My 7890's with an FID run in that 1.2-1.7 range (at oven = 40 °C, detector at 240 °C) as well. I had to make the same adjustment. However, I have the freedom to do so without consulting anyone for approval.

[James_Ball]

I would think "bumping up" the signal through a setting on the keypad would be more of a method violation than adjusting the lit offset.

The lit offset would affect the results no more than adjusting the oven maximum temperature to a value higher than the highest temperature used in the oven ramp, it changes nothing as far as the calibration or results are concerned. If it has been written into the SOP then it is something to be looked at in the next revision. Some things get written into controlled documents that really don't belong there. It would be akin to putting in the SOP that you can only load samples onto the autosampler try with your left hand.