Chromatography Forum

I am having an issue with my GC-MS where I have repeating peaks in my baseline. The attached images are from no-injection blank runs with a gradient from 100 to 200 C; however, this occurs under isothermal conditions as well.

The second image shows the difference at different flow rates where the time delta between peaks is very similar (~0.14 min).

The mass spectra of these peaks are showing a primary peak at 32 with a second peak at 40 (both show spikes in their respective EICs).

I've tightened all connections and "baked out" MS. The air/water check in the MS is all fine (H2O: 1.2%; O2: 1.0%; N2: 3.3%)

Has anyone encountered this before?



Different flow rates (0.8 & 1.2 mL/min)

Whatever it is, it is happening every ~7 seconds. That should help you track it down. I'd look for something opening/closing unexpectedly, power fluctuations, a relay going bad... If you can't find a setting somewhere or hear/see whatever it is, you may need to bring service in to check the electronics.

That it continues at the same rate despite a change in flow would make me want to focus on the MSD, not the GC.

Thanks for the reply DR. There's nothing visible/audible corresponding to the peaks. I can't say I know enough about the electronics to check it, but the fact that only select ions are producing the peaks, that led me to believe it was not electronic. I could be incorrect in this assumption though.

I'm pretty much a MSD novice myself, I'd be inclined to call the vendor for a consultation or service...

32 and 40 sound like it would be oxygen and argon causing the peaks, which would come from air. What is the scan range during the run? If scanning above 28 you could me missing the nitrogen from an air leak.

What are more of the details of the instrument? Injection port, injection type, MS and GC models, scan range. More details the better to help trouble shoot.