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US 5,324,939 AGranted
Method and apparatus for ejecting unwanted ions in an ion trap mass spectrometer
AssigneeFinnigan Corporation
InventorsJohn N. Louris, Dennis M. Taylor
Life of this patent
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Abstract
A method and apparatus is described which determines a plurality of spaced discrete frequencies covering the range of frequencies of the characteristic motion of unwanted ions and processes said discrete frequencies to generate a plurality of time dependent voltage amplitude values which vary throughout the time domain such that the frequency content of said plurality of time dependent voltage amplitude values is relatively uniform over the entire time domain, and such that the magnitude associated with the discrete frequencies is relatively uniform over the frequency domain.
Claims26
An ion trap mass spectrometer apparatus comprising:
- an ion trap having a plurality of electrodes,
- means for establishing ion trapping fields within said ion trap for trapping ions over a predetermined mass range,
- ion excitation means for resonantly ejecting ions trapped in said ion trap including:
- means for determining a plurality of spaced discrete frequencies covering the range of frequencies of the characteristic motion of ions which are to be resonantly ejected from the ion trap,
- means for processing said discrete frequencies to generate a plurality of time dependent voltage amplitude values which vary throughout the time domain such that the frequency content of said time dependent voltage amplitude values is relatively uniform over the entire time domain, and such that the magnitude of the discrete frequencies is relatively uniform over the frequency domain, and
- means for applying said time dependent voltage amplitude values to said ion trap electrodes whereby to resonantly eject said ions.
3 more elements
A method for resonantly ejecting ions stored in an ion trap comprising the steps of
- determining a plurality of spaced discrete frequencies covering the range of frequencies of characteristic motion of the ions which are to be resonantly ejected,
- processing said discrete frequencies to generate a plurality of time dependent voltage amplitude values which vary throughout the time domain such that the frequency content of said time dependent voltage amplitude values is relatively uniform over the entire time domain, and such that the magnitude of the discrete frequencies is relatively uniform over the frequency domain, and
- applying said time dependent voltage amplitude values to said ion trap electrodes whereby to resonantly eject said ions.
A method for resonantly ejecting ions stored in the ion trap of a mass spectrometer which stores ions over a predetermined mass range including the steps of:
- determining a series of spaced sine functions which have phases that vary non-linearly with frequency, said sine functions covering the range of frequencies of the characteristic motion of ions to be ejected,
- summing the series of sine functions to provide a waveform which has a series of closely spaced discretely separated peaks in the frequency domain, such that the difference in ejection efficiency between an ion having a characteristic frequency of motion which coincides with a discrete frequency component of the waveform, and an ion having a characteristic frequency of motion which falls between the discrete frequency components of the waveform is small, and
- applying said waveform to the ion trap to resonantly eject selected ions.
A method for resonantly ejecting ions stored in an ion trap including the steps of:
- determining a series of spaced sine functions which have phases that vary non-linearly with frequency, said sine functions covering the range of frequencies of the characteristic motion of ions to be ejected,
- summing the series of sine functions to provide a waveform which has a series of spaced discretely separated peaks in the frequency domain, such that the difference in frequencies between successive discretely separated peaks in the frequency domain is at least four times the reciprocal of the time interval over which the waveform is to be applied, and
- applying said waveform to the ion trap to resonantly eject selected ions.
A method for resonantly ejecting ions stored in an ion trap including the steps of:
- determining a series of spaced sine functions which have phases that vary non-linearly with frequency, said sine functions covering the range of frequencies of the characteristic motion of ions to be ejected,
- summing the series of sine functions to provide a waveform which has a series of spaced discretely separated peaks in the frequency domain, such that the difference in frequencies between successive discretely separated peaks in the frequency domain is at least two times the reciprocal of the time interval over which the waveform is to be applied, and
- applying said waveform to the ion trap to resonantly eject selected ions.
A method for resonantly ejecting ions stored in an ion trap including the steps of:
- calculating a waveform in which the magnitude part of the frequency spectrum is assigned in such a way that the frequency spectrum substantially consists of a series of discretely separated peaks covering a range of frequencies corresponding to the characteristic frequencies of ions to be ejected and in which the phase part of the frequency spectrum is assigned as a nonlinear function of frequency and in which the time domain waveform is calculated by application of the inverse Fourier transform, and
- applying said waveform to the ion trap to resonantly eject selected ions.
A method for resonantly ejecting ions stored in an ion trap including the steps of:
- calculating a waveform in which the magnitude part of the frequency spectrum is assigned in such a way that the frequency spectrum substantially consists of a series of discretely separated peaks covering a range of frequencies corresponding to the characteristic frequencies of ions to be ejected and such that the difference in frequencies between the successive peaks in the frequency domain is at least four times the reciprocal of the time interval over which the waveform is to be applied, and in which the phase part of the frequency spectrum is assigned as a nonlinear function of frequency and in which the time domain waveform is calculated by application of the inverse Fourier transform, and
- applying said waveform to the ion trap to resonantly eject selected ions.
A method for resonantly ejecting ions stored in an ion trap including the steps of:
- calculating a waveform in which the magnitude part of the frequency spectrum is assigned in such a way that the frequency spectrum substantially consists of a series of discretely separated peaks covering a range of frequencies corresponding to the characteristic frequencies of ions to be ejected and such that the difference in frequencies between the successive peaks in the frequency domain is at least two times the reciprocal of the time interval over which the waveform is to be applied, and in which the phase part of the frequency spectrum is assigned as a nonlinear function of frequency and in which the time domain waveform is calculated by application of the inverse Fourier transform, and
- applying said waveform to the ion trap to resonantly eject selected ions.
A method for resonantly ejecting ions stored in an ion trap including the steps of:
- calculating a waveform in which the magnitude part of the frequency spectrum is substantially a series of discretely separated peaks covering a range of frequencies corresponding to the characteristic frequencies of ions to be ejected, and
- applying said waveform to the ion trap to resonantly eject selected ions.
A method for resonantly ejecting ions stored in an ion trap including the steps of:
- calculating a waveform in which the magnitude part of the frequency spectrum substantially consists of a series of discretely separated peaks covering a range of frequencies corresponding to the characteristic frequencies of ions to be ejected and such that the difference in frequencies between the successive peaks in the frequency domain is at least four times the reciprocal of the time interval over which the waveform is to be applied, and p1 applying said waveform to the ion trap to resonantly eject selected ions.
A method for resonantly ejecting ions stored in an ion trap including the steps of:
- calculating a waveform in which the magnitude part of the frequency spectrum substantially consists of a series of discretely separated peaks covering a range of frequencies corresponding to the characteristic frequencies of ions to be ejected and such that the difference in frequencies between the successive peaks in the frequency domain is at least two times the reciprocal of the time interval over which the waveform is to be applied, and
- applying said waveform to the ion trap to resonantly eject selected ions.
Dependencies are inferred from the claim text.