FOURIER-TRANSFORM MASS-SPECTROMETRIC DETECTION OF SUSPENDED TRAPPING MEASUREMENTS WITH A VARIABLE LENGTH EXTERNAL ION RESERVOIR

The effect of Fourier transform mass spectrometry (FTMS) suspended trapping events on the evolution of ion cloud spatial and kinetic energy distributions during ion flight is evaluated by FTMS. A probe-mounted electrode permits the initial formation of ions in variable length reservoirs adjacent to the trapped ion cells to facilitate these measurements. Several experiments are presented to demonstrate the versatility of the apparatus. For example, FTMS-time-of-flight (TOF) detection of ion flight from the trapped ion cell is used to investigate collisional relaxation. In another experiment, the kinetic energy of FTMS-detected ions entering the trapped ion cell following a suspension of trapping potentials is found by time-of-flight analysis to be less than 0.1 eV, independent of initial trap potential. The reservoir is used to directly observe the trapping oscillations of ions in elongated wells up to 43 cm in length. The trapping period is found to vary proportionally with cell length, in contrast to present models for the motion. Finally, the utility of suspended trapping for alleviating space charge effects is demonstrated. © 1990.