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- Posts: 8
- Joined: Thu May 10, 2012 6:33 pm
Hello all!
I have a recurring problem with my mass chromatograms that I can't troubleshoot, so I decided to post here to have your input. I have an LC-MS (Waters Alliance LC coupled with a LC platform as my mass spectrometer) system and recently, I have seen random negative shifts of my baseline in my mass chromatograms. These shifts can occur anywhere during my 20 minutes gradient method and they always last between 3 to 4 minutes. Below is a chromatogram of a caffeine injection where you can see the shift between 12 and 16 minutes:
Below is another injection of caffeine done right before, where the baseline is perfectly fine.
The thing is, that if an analyte elutes at the same moment where these random negative shifts occur, I can't see any peak at all. The temporary fix I have found is to simply reinject my sample and I will have a normal mass chromatogram. However, this problem happens quite frequently and I'm looking for a more permanent solution.
As for the troubleshooting I have done so far, I have tried both an electrospray and an APcI probe and both of them show this problem. I have also cleaned various parts of my mass spectrometers (sample cone, probe, counter-electrodes, even the hexapole) but that didn't change anything. As a last bit of information, I have done these two injections in a mobile phase containing 0.1% TFA but I have also observed this problem with other additives, such as formic acid.
Thank you very much for every bit of help you can provide,
agoupax
I have a recurring problem with my mass chromatograms that I can't troubleshoot, so I decided to post here to have your input. I have an LC-MS (Waters Alliance LC coupled with a LC platform as my mass spectrometer) system and recently, I have seen random negative shifts of my baseline in my mass chromatograms. These shifts can occur anywhere during my 20 minutes gradient method and they always last between 3 to 4 minutes. Below is a chromatogram of a caffeine injection where you can see the shift between 12 and 16 minutes:
Below is another injection of caffeine done right before, where the baseline is perfectly fine.
The thing is, that if an analyte elutes at the same moment where these random negative shifts occur, I can't see any peak at all. The temporary fix I have found is to simply reinject my sample and I will have a normal mass chromatogram. However, this problem happens quite frequently and I'm looking for a more permanent solution.
As for the troubleshooting I have done so far, I have tried both an electrospray and an APcI probe and both of them show this problem. I have also cleaned various parts of my mass spectrometers (sample cone, probe, counter-electrodes, even the hexapole) but that didn't change anything. As a last bit of information, I have done these two injections in a mobile phase containing 0.1% TFA but I have also observed this problem with other additives, such as formic acid.
Thank you very much for every bit of help you can provide,
agoupax
