Fluctuating baseline - GC-TOFMS
Posted: Mon Sep 23, 2019 9:18 pm
Please let me know if anyone can help me troubleshoot my baseline issue.
https://imgur.com/jTP8BT5
https://imgur.com/p4KH9Gp
https://imgur.com/cWqStAY
These image links are 3 pictures of the same hexane blank run. The top image is the unprocessed raw chromatogram (exhibits the baseline fluctuations), the second image is the processed TIC and the third image is the processed chromatogram AIC view.
Background Info: This is a GCxGC-TOFMS (LECO Pegasus 4D) but is currently running only in a 1-dimensional mode. I have been running the same GC and MS methods for a while and after doing inlet maintenance/changing the secondary column this baseline fluctuation started happening. The chromatogram shown in the image below is a run of a hexane blank and should show some noise but overall should trend as a flat baseline. The method is tuned for C7 - C31 hydrocarbons and I have been running samples on it from sediment extractions until this started happening.
I have tried to identify the problem by changing many parameters of the GC and MS methods but nothing has helped. The only leads I have are that when running the GC-MS with no injection and the primary oven set to 50 C (isothermal run), I still see these "humps". This indicates to me that contamination is not the issue and that the problem is either with the carrier gas (which was changed and did not help) or an issue with the MS. Please let me know if you have ever run into a problem like this and have any suggestions. Feel free to ask questions. Thanks
https://imgur.com/jTP8BT5
https://imgur.com/p4KH9Gp
https://imgur.com/cWqStAY
These image links are 3 pictures of the same hexane blank run. The top image is the unprocessed raw chromatogram (exhibits the baseline fluctuations), the second image is the processed TIC and the third image is the processed chromatogram AIC view.
Background Info: This is a GCxGC-TOFMS (LECO Pegasus 4D) but is currently running only in a 1-dimensional mode. I have been running the same GC and MS methods for a while and after doing inlet maintenance/changing the secondary column this baseline fluctuation started happening. The chromatogram shown in the image below is a run of a hexane blank and should show some noise but overall should trend as a flat baseline. The method is tuned for C7 - C31 hydrocarbons and I have been running samples on it from sediment extractions until this started happening.
I have tried to identify the problem by changing many parameters of the GC and MS methods but nothing has helped. The only leads I have are that when running the GC-MS with no injection and the primary oven set to 50 C (isothermal run), I still see these "humps". This indicates to me that contamination is not the issue and that the problem is either with the carrier gas (which was changed and did not help) or an issue with the MS. Please let me know if you have ever run into a problem like this and have any suggestions. Feel free to ask questions. Thanks