Evaluation of spectra in oscillation mass spectrometers
The invention relates to mass spectrometers in which ion clouds are stored in two spatial directions by radial forces while oscillating largely harmonically at a mass-specific frequency in a third spatial direction perpendicular to the other two, in a potential minimum, the shape of which is as close to a parabola as possible. Analysis of the oscillation frequencies of these ion clouds, preferably by a Fourier analysis, leads via a frequency spectrum to a mass spectrum. The frequency spectrum is analyzed to identify false signals in the frequency spectrum as harmonics and eliminating them where necessary.
1. A method of evaluating a frequency spectrum of a plurality of analyte ions obtained in an oscillation mass spectrometer, comprising:
investigating a plurality of frequency components within the frequency spectrum by identifying for each of the frequency components whether the frequency component is associated with a fundamental oscillation of the analyte ions or a harmonic of the fundamental oscillation; and
attenuating the frequency components associated with the harmonics.
2. The method of claim 1 , wherein in order to identify harmonics, analyses are carried out in the frequency spectrum to establish, for a plurality of oscillation signals, whether other oscillation signals examined have an integer fraction of the frequency of the oscillation signal under analysis.
3. The method of claim 1 , wherein in order to identify harmonics, analyses are carried out in the frequency spectrum to establish, for a plurality of oscillation signals, whether other oscillation signals examined have an integer multiple of the frequency of the oscillation signal under analysis.
4. The method of claim 1 , wherein an instrument-specific spectrum of the harmonics is measured for an oscillation mass spectrometer, and the signal height ratios of the spectrum of the harmonics are used to identify a signal as a harmonic.
5. The method of claim 1 , wherein all signals of an isotope group are used to corroborate a signal as a harmonic.
6. The method of claim 5 , wherein in order to identify a signal as a harmonic, the signal height ratios within the isotope group for the harmonics must agree with those of the fundamental oscillations.
7. A system for evaluating a frequency spectrum of a plurality of analyte ions obtained in an oscillation mass spectrometer, comprising:
means for investigating a plurality of frequency components within the frequency spectrum by identifying for each of the plurality of frequency components whether the frequency component is associated with a fundamental oscillation of the analyte ions or a harmonic of the fundamental oscillation; and
means for attenuating the frequency components associated with the harmonics from the frequency spectrum.
8. A method of automatically evaluating a frequency spectrum obtained in an oscillation mass spectrometer, comprising:
reading ion currents within the oscillation mass spectrometer and providing an ion current signal indicative thereof;
transforming the ion current signal from the time domain to the frequency domain and providing frequency data indicative thereof;
analyzing the frequency data to determine harmonic frequency components within the frequency data;
processing the frequency data to attenuate the detected harmonic frequency components from the frequency data to provide corrected frequency data; and
converting the corrected frequency data to a mass list.
9. The method of claim 8 , where the steps of transforming comprises performing a Fourier analysis.
10. The method of claim 8 , where the steps of transforming comprises performing a Fast Fourier Transform.
11. The method of claim 10 , where the step of processing includes assigning a zero value to the amplitude value of a detected harmonic.