Multiparticle Simulation of Ion Injection into the Quadrupole Ion Trap Under the Influence of Helium Buffer Gas Using Short Injection Times and DC Pulse Potentials
✍ Scribed by C. Weil; M. Nappi; C. D. Cleven; H. Wollnik; R. G. Cooks
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 953 KB
- Volume
- 10
- Category
- Article
- ISSN
- 0951-4198
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✦ Synopsis
The motion of an ensemble of ions during their gated injection into the three-dimensional radio-frequency quadrupole ion trap was simulated considering helium buffer gas collisions, injection at certain RF phase angles and using DC impulsive fields to optimize the trapping efficiency. Simulations using a simple model of ionneutral collisions show that buffer gas alone, even at 1-10 mTorr pressure, is not able to remove sufficient kinetic energy from the injected ions through ion-neutral collisions to prevent their loss and does not solve the problem of low efficiency of ion retention in the trap, even under q,-optimization. Accumulation of ions over long periods is not very effective, in such cases trapping efficiencies are less than 5%. It is shown that under F W phase angles between 110" and 220" the injected ions can be trapped, although only temporarily, with very high efficiencies. The simulations lead to the conclusion that all of the desired injected ions covering a wide masslcharge range can be trapped for indefinite times when short injection pulses are used together with dipolar DC pulses applied during injection. The additional damping achieved through these dipolar DC impulsive fields and the resulting cooling of the ion cloud is shown to give efficient trapping.