Abstract: Tailored excitation of ions in a mass spectrometer is obtained by using an excitation signal which comprises at least one signal having the form of a sinc function modulated sine wave. The sinc modulated sine wave has a magnitude function in the frequency domain in the form of a rectangular function centered at the frequency of the sine wave and having a width determined by the width of the sinc function. Plural sinc modulated sine wave signals can be applied to the ion trap of the spectrometer, with the various signals having different sine wave frequencies, to provide a tailored excitation spectrum without the need for extended computation.

Abstract: A desired mass domain excitation profile is selected and converted to a frequency domain excitation spectrum in which the frequency of excitation is generally proportional to the inverse of the mass-to-charge ratio. In the direct method of the invention, the specified frequency domain spectrum is converted by inverse Fourier transformation to a time domain waveform and multiplied by an expanded window function. The time domain waveform is forward Fourier transformed to produce a second discrete frequency spectrum each frequency of which is assigned a phase scrambled such that maximum reduction of peak excitation voltage is achieved with no distortion of the excitation amplitude spectrum. The phase-scrambled frequency spectrum is inverse Fourier transformed to produce the final time domain waveform which is used to generate the electric field which excites the ions in an ion cyclotron resonance cell.

Abstract: An ion cyclotron resonance mass spectrometer is externally calibrated, i.e. a calibrant compound is not present at the same time as the sample to be analyzed, by determining changes in the relative number of ions in the cell. This may be done by obtaining a spectrum of the sample to be analyzed, measuring the trapping sidebands, and then determining the trapping frequency from those sidebands as the difference between the trapping sideband frequencies and divided by four. The cyclotron frequency can then be found from the effective measured frequency and the trapping frequency, and the mass is then obtained as a function of the cyclotron frequency. Another approach is to measure the magnetron frequency directly, and then to calculate the cyclotron frequency from the measured effective frequency and the magnetron frequency. A third approach is to introduce a calibrant compound into the cell and produce several output signals with various relative numbers of ions.