Ghost peaks and sudden baseline shifts

5975C MSD and 7890 GC. I am fairly new to GC-MS and am having issues with my baseline. I have recently begun seeing ghost peaks and sudden baseline shifts after replacing a column. I did inlet maintenance and added an in-line gas purifier as well as conditioned the column to help resolve, but the bottom spectra which was run after this maintenance is actually showing the ghost peaks again as well as the sudden baseline shifts I saw before. 

Could this be a detector issue? I have a CI detector but know nothing about how to clean or troubleshoot it. 

  • No, I didn't realize that. The lightest component I would be interested in is around 44 MW. Do I do that via the Tune and Vaccum menu?

  • No it's in the method. Go to edit entire method and go through the screens. I forget exactly where it is in the MS area of the method, just look around or look in the manual if you have one or the help in the software.

  • You can change your scan range under MS Parameters.  Go to Method and Run Control view, I think it is Instrument menu, Edit MS Parameters.

    Some gas filters cartridges are filled with N2 during manufacturing for shipping, so it takes some time after installation to purge it all out.  The low O2 shows that it's not a leak.  (Air leak would have N2/O2 ratio approx. 4.)  Agilent's Gas Clean filters are like this.  When I install one on a new system, I'll set the split flow to 250-300 mL/min overnight to purge the N2 from the filter.  Argon (40) sometimes shows up as an impurity in helium, and a gas filter won't remove it.

  • Interesting about the N2 in the filters. The N2 content does seem to be coming down slowly, but last check still showed over 10%. O2 and H2O numbers are low. I did find a large leak on a helium regulator further downstream of the regulator supplying the GC-MS so isolated that regulator, but it didn't seem to help bring my N2 numbers down much. Question, if I had an O2 scrubber in-line, couldn't that remove most of the O2 and skew the N2 to O2 numbers so they weren't 4:1?

     

    I really appreciate all the help and suggestions regarding my issue. I am still learning about MSDs and feel like I have a long way to go. Meanwhile, the baseline is much improved and most of the ghost peaks seem to have vanished.

  • You're correct: a leak before the gas filter can result in high N2, as the O2 would get captured by the filter.  When I see the high N2 with low O2, the cause is typically: 1) filter needs more time to purge, 2) leak ahead of filter, 3) impurity in the gas cylinder.

     

    In terms of learning about your system, Agilent has training resources available.  There are frequent webinars on various topics, and past ones are available for viewing at your leisure.  The GC/GCMS webinars can be found at: GC & GC/MS Webinars | Agilent 

     

    I would also recommend looking at Agilent University.  There are hundreds of courses on Agilent hardware and software.  If travel is a problem, some of the material is virtual/online class, and some is self-paced e-learning.  Some material is free, but others require training credits to register.  More information can be found at: Agilent University | Agilent 

  • I'm seeing better baseline and no ghost peaks even with leaving the scan range at what it is now. 

    Thanks very much for the help and i will definitely look into those continuing ed courses on GC-MS.

     

    Karen

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