Ion injection and activation in the quadrupole ion trap mass spectrometer

Kenneth Lee Morand, Purdue University

Abstract

The initial fascination and excitement surrounding the introduction of any new analytical instrument is quite often followed by intense scientific experimentation and development. It is the goal of this thesis to provide additional understanding concerning ion injection and ion activation in the quadrupole ion trap mass spectrometer. With the introduction of mass-to-charge range extension and high resolution capabilities on the ion trap mass spectrometry has come a variety of applications concerned with the analysis large proteins and biomolecules. However, such experiments have been plagued by limited mass measurement accuracy as ions are not ejected in a predictable manner. Examination of the solution to the "forced", "damped" Mathieu equation and a thorough understanding of the behavior of ions under the influence of space charge allow a qualitative prediction of ion behavior and such predictions have a direct outcome on the ability to perform experiments with high mass accuracy. For ions which are sufficiently separated in m/z ratio, mass measurement errors occur as a result of off-resonance energy absorption by the ion which leads to early ejection of the ion, while errors for ions which are in close proximity, $\le$1 da/charge separation, result from combination of off-resonance absorption and the presence of space charge conditions which lead to irregular peak separations. However, the analysis of large biomolecules requires the efficient collection of ions injected into the trap and energy deposition processes which were not typically available. The use of a combination of the helium buffer gas with a small amount of a heavier mass target effects both the trapping efficiency and the deposition of much higher internal energies in the selected ion without deleterious effects of ion loss due to scattering. For ions with m/z ratios greater than 8000 da/charge the use of buffer mixtures is shown to increase the trapping efficiency by as much as 200%. In addition, collision-induced dissociation experiments performed on thermometer-type species, such as pyrene, confirm that up to 23 volts of internal energy may be deposited in a single MS/MS experiment and should be applicable for the dissociation of biomolecules.

Degree

Ph.D.

Advisors

Cooks, Purdue University.

Subject Area

Analytical chemistry

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