When several quinoline derivatives were fragmentated via LC/ESI-MS (mass tolerance m/z: 0.3), it often occurred that the wanted M+H+ values showed a low intensity (for example m/z 162). In the meantime, very high intensities were measured for a mass which m/z value was one unit larger (m/z 163) than the respective M+H+. This should not be the case, since the mass tolernace was set for +/- 0.3 m/z
It was odd, since during MS1 runs, I only detected the expected masses for the quinoline derivatives but no elevated masses as in MS2 runs. So therefore, it is unlikely, that the device needed a recalibration.
Literature search did not help to solve this enigma. Has anyone ever heard of something similiar?
Did you mean that you search the extracted ion chromatogram for m/z 162 with a tolerance of +/- 0.3 and only found m/z 163? Did you try to reduce this tolerance?
Mr. Sartor,
A difference in Dm/z = +/-1 can be a result from clusters of analytes. Currently, we carry out such analysis of Zn2+ species. (The data should be appeared in the near future.)
Such ions can be quantified accurately only by an accurate determination of the MS intensity of the peaks. Among the currenly, available methods for quantitative treatment of the MS intensity, an acurate and precise descrition in chemometric terms of the MS outcome 'intensity' can be carried out only by means of our method and formulas.
In this context, please, consider the following Conference presentation and the reference section, therein:
Conference Paper Mass spectrometric diffusion parameters and 3D structural an...
You mention about quinolone derivatives - doest it mean you do a chemical derivatisation to ionise these compounds? If so, I would try some other compounds to check for their mass accuracy,
If it is still off, either one of the quadrupole might have the calibration off.
Dear Pascal,
Unfortunately, you haven't provided additional information such vendor and model of your mass spectrometer.
Judging by the scan types, MS1 and MS2, mentioned in your question, I can suppose the you use SCIEX triple quad. If so, its quadrupoles Q1 and Q3 need separate calibration, and it's quite possible that one of them can work incorrectly.
I have met similar problem in neutral loss experiments, when we observed mysterious signals for SOME samples from a batch. Firstly, we were glad to see something new, but after recalibration of the MS these signals disappeared.
I have a short guide on how to tune and calibrate SCIEX mass specs, so, if necessary, I can send it to you.
Thank you all for your suggestions.
The device (amazon speed, bruker) was recalibrated by the manufactorer last week (independently of my case), and it was mentioned that its calibration was slightly off normal values. I'm currently repeating the experiments with an optimized protocol and an C18 HPLC column instead of a C8 column to get sharper peaks which could perhaps lead to sharper fragmentation patterns.
It might be, that the fragmentation by chemically induced dissociation is too strong, I will also check if a weaker setting will prevent the presence of those suspicious masses.
The mystery has been solved.
Fragmentation data was analyzed by the MS device custom service. They said, that the the selected mass was fragmentated (therefore its intensity dropped) and due to the narrow mass window used for fragmentation ( +/- 0.3 m/z) the mass of the next heavier isotope (the "elevated mass") was selected poorly as well (roughly one percent of its intensity in MS1 runs were found in MS2 runs). However, it was not fragmentated so its intensity appeared huge when compared to the (low) intensity of the actually selected mass.
Recently performed experiments with an allowed mass deviation of +/- 3 m/z selected for the complete isotope spectrum of my compound and resulted in nice fragmentation patterns.
I'm glad this problem is solved now, and thank you all for your comments.
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