Aa. Makarov, RESONANCE EJECTION FROM THE PAUL TRAP - A THEORETICAL TREATMENT INCORPORATING A WEAK OCTAPOLE FIELD, Analytical chemistry, 68(23), 1996, pp. 4257-4263
In response to the growing experimental evidence of the importance of
nonlinear phenomena in ion trap operation, a new theoretical model of
ion ejection is developed. The pseudopotential well approximation for
forced ion oscillations in an ion trap under the conditions of ion-mol
ecule collisions is modified to include octapole perturbations on the
quadrupole field. Ion ejection is investigated using the first-order M
itropol'skii asymptotic method for both infinitesimal and finite scan
rates. It is shown that the combined action of collisional damping and
nonlinearity distorts the resonance curve in such a way that ''quench
ing'' of oscillations takes place. As a result, with appropriate excit
ation and direction of scanning, the amplitude increases as if no damp
ing exists! The main characteristics of the jump are derived as functi
ons of scan rate and used for analytical estimation of mass resolution
, mass peak width, and excitation voltage. Satisfactory agreement betw
een calculated and experimental peak widths is demonstrated for the ra
nge of scanning rates in excess of 6 orders of magnitude.