Characteristics of stability boundary and frequency in nonlinear ion trap mass spectrometer |
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Authors: | Xiaoyu Zhou Zhiqiang Zhu Caiqiao Xiong Rui Chen Wenjun Xu Haoxue Qiao Wen-Ping Peng Zongxiu Nie Yi Chen |
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Institution: | (1) Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry Chinese Academy of Sciences, Beijing, China; Beijing National Laboratory for Molecular Sciences, Beijing, 100190, China;(2) Department of Physics, Wuhan University, Wuhan, China;(3) School of Sciences, Jiujiang University, Jiujiang, China;(4) Jiujiang Vocational University, Jiujiang, China;(5) Department of Physics, National Dong Hwa University, Shoufeng, Hualien, 97401, Taiwan |
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Abstract: | In this article, the Poincare-Lighthill-Kuo (PLK) method is used to derive an analytical expression on the stability boundary
and the ion trajectory. A multipole superposition model mainly including octopole component is adopted to represent the inhomogeneities
of the field. In this method, both the motional displacement and secular frequency of ions have been expanded to asymptotic
series by the scale of nonlinear term ε, which represents a weak octopole field. By solving the zero and first-order approximate
equations, it is found that a frequency shift exists between the ideal and nonlinear conditions. The motional frequency of
ions in nonlinear ion trap depends on not only Mathieu parameters, a and q, but also the percentage of the nonlinear field and the initial amplitude of ions. In the same trap, ions have the same mass-to-charge
ratio (m/z) but they have different initial amplitudes or velocities. Consequently, they will be ejected at different time through after
a mass-selective instability scan. The influences on the mass resolution in quadrupole ion trap, which is coupled with positive
or negative octopole fields, have been discussed respectively. |
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Keywords: | |
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