EXTENDED THEORETICAL CONSIDERATIONS FOR MASS RESOLUTION IN THE RESONANCE EJECTION MODE OF QUADRUPOLE ION-TRAP MASS-SPECTROMETRY

Proceeding from the pseudopotential-well approximation for ion motion in a quadrupole ion trap, mathematical expressions are derived to desc ribe the excitation amplitude of an ion packet at a given mass-to-char ge ratio. Ion-neutral collisions are incorporated to describe the damp ing of ion trajectories and to describe the distribution of individual ion trajectories about a mean amplitude for the ion packet. The rate of increase of the amplitude during scanning is related to expressions that describe the amplitude dispersion of the ions at the time of eje ction from the trap, which is operating in a resonance ejection scanni ng mode to describe the temporal line width of the ejected ion packet. The temporal fine width is related to mass resolution under a number of different scanning conditions. Included in the discussion are consi derations of the effect on resolution of the resonance excitation volt age, temperature, pressure, noise, and buffer-gas composition. An expr ession for the maximum possible resolution at high ion mass-to-charge ratios is developed, and these results are compared to an existing the oretical construction. The expressions derived under the pseudopotenti al-well approximation are further extended to high q(z) values and com pared to experimental data previously published by two other researche rs.