RESONANT EXCITATION AND OR EJECTION OF IONS SUBJECTED TO DC AND RF FIELDS IN A COMMERCIAL QUADRUPOLE ION-TRAP/

An empirical method has been proposed for the prediction of the freque ncy at which optimum resonant excitation can be achieved for ions conf ined in a quadrupole ion trap. The method, which can be used for both ion excitation and ion ejection, is based upon the changes which can o ccur in ion axial and radial secular frequencies as the excursions of ion trajectories increase from the centre of the ion trap. The changes in ion axial and radial secular frequencies wrought by optimum ion ex citation can be expressed in terms of an equivalent direct current (DC ) potential applied to the ion trap ring electrode; the method has bee n tested in three experiments in which DC potentials have been applied . (C) 1997 by John Wiley & Sons, Ltd.