Stored waveform inverse Fourier transform axial excitation/ejection for quadrupole ion trap mass spectrometry.
A general method for high-resolution ion excitation, ejection, and isolation is developed from linear response theory for resonant dipolar excitation of the axial z-oscillatory motion of ions in a quadrupole (Paul) ion trap operated in rf-only mode. For a spatially uniform dipolar excitation field, the ion z-oscillation amplitude is directly proportional to the amplitude of the Fourier component of the excitation at the axial oscillation frequency of that ion. Thus, one may specify an arbitrary z-motion frequency-domain spectrum by applying a time-domain stored waveform obtained from the inverse Fourier transform of the corresponding frequency-domain excitation spectrum. The stored waveform inverse Fourier transform (SWIFT) waveform may be tailored for selective ejection or excitation of ions of arbitrary mass-to-charge ratio ranges. The method includes all other possible excitation/ejection waveforms (e.g., single frequency, frequency sweep) as special cases. The effect of collisional damping during excitation is included in the analytical solution of the ion response.
Department of Chemistry, Ohio State University, Columbus 43210.
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Guan
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Marshall
D000465:Algorithms; D005583:Fourier Analysis; D013058:Mass Spectrometry / Q000379:methods*; D008962:Models, Theoretical