Axial ion motion within the quadrupole ion trap elucidated by dc pulse tomography

A new experimental technique is described for probing the motion of ions in a quadrupole ion trap via the application of short de pulses to one endcap electrode. The method, which arose from simulations conducted using a mult i-ion simulation program, ITSIM, reveals details of the motion of trapped i ons and allows experimental measurement of the ion secular frequency. It is shown that a short dc pulse having the appropriate phase relationship with respect to the phase of oscillation of a population of trapped ions may be used to activate and eject chosen species from the trap while leaving othe r ions, even isobaric ions, relatively unperturbed. This provides a possibl e basis for high resolution collisional activation and high resolution mass analysis in the Paul trap. (Int J Mass Spectrom 194 (2000) 225-234) (C) 20 00 Elsevier Science B.V.