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Parametric resonances and a high-pressure RF-only-mode event in Fourier transform mass spectrometry
Abstract
The dissertation describes two roles that the electric-trapping field can play in the detection of ions by Fourier transform mass spectrometry (FTMS). In the first study (Chapter 2) the proper ideal for the shape of the electric-trapping well is considered. Numerical calculations show that non-quadrupolar trapping potentials result in the parametric coupling of the axial and radial motions of the ions. This coupling causes the ion cloud to expand radially. The detection performance of high mass-to-charge ions in a 7-tesla magnetic field were modeled by the benzene molecular ion under scaling conditions and showed a loss of detection performance over the same m/q ranges that were predicted to satisfy the resonance condition in the cubic cell. Additional calculations show that parametric resonances become broader and the rate of radial expansion greater as the trapping potential becomes more anharmonic. The study concludes that the quadrupolar potential is the proper ideal for FTMS. The second study (Chapter 3) details the operation of the FT-mass spectrometer under the high pressure conditions of a new event in the FTMS sequence called an RF-only-mode event. During the event an rf-potential is superimposed onto the normally static trapping potential so that the FTMS operates as a QUISTOR. The utility of the event is demonstrated with the $\beta$-distonic adduct of the pyridine radical cation and ethene neutral. This adduct forms with sufficient internal energy that it decomposes and cannot be observed in the low pressure conditions of FTMS. The study demonstrates that the adduct is detected if it is collisionally stabilized during its formation with the high pressure of an RF-only-mode event. As an early probe of reactivity, it is shown that molecular oxygen reacts selectively with the radical site of the $\beta$-distonic ion but not with the radical cations of the ion's isomers. The experimental chapters are proceeded by a review of FTMS fundamentals and recent advances that are extending the m/q range of FTMS.
Subject Area
Analytical chemistry
Recommended Citation
Holliman, Christopher Lee, "Parametric resonances and a high-pressure RF-only-mode event in Fourier transform mass spectrometry" (1994). ETD collection for University of Nebraska-Lincoln. AAI9507812.
https://digitalcommons.unl.edu/dissertations/AAI9507812