Method for analyzing a gas by mass spectrometry, and mass spectrometer

A method, comprising:

• exciting ions of a gas in an FT ion trap;
• recording a first frequency spectrum comprising:
• a) peaks corresponding to ion frequencies for ion signals generated by the excited ions;
• and b) peaks corresponding to interference frequencies;
• recording a second frequency spectrum comprising peaks corresponding to the interference frequencies of the first frequency spectrum but not peaks corresponding to ion frequencies for ion signals generated by the excited ions;
• and
• comparing the first and second frequency spectra to identify the interference frequencies of the first frequency spectrum.

A mass spectrometer, comprising:

• an FT ion trap;
• a detector configured to record:
• a first frequency spectrum in a first measuring time interval during or after excitation of ions in the ion trap, the first frequency spectrum comprising peaks corresponding to ion frequencies for ion signals generated by the excited ions and peaks corresponding to interference frequencies;
• and
• a second frequency spectrum in a second measuring time interval, the second frequency spectrum comprising the peaks corresponding to the interference frequencies of the first frequency spectrum but not peaks corresponding to ion frequencies for ion signals generated by the excited ions,
• wherein the detector is configured to identify the interference frequencies of the first frequency spectrum by comparing the first and second frequency spectra.