The structural characterization of ions in the gas phase by using tandem mass spectrometry and the characterization of the performance of an FT/ICR based on a permanent magnet

Loreen Cecilia Zeller, Purdue University

Abstract

The gas-phase structures of the radical cations of organophosphorus esters and thioesters have been studied in a Fourier transform ion cyclotron resonance (FT/ICR) mass spectrometer and the performance of an FT/ICR mass spectrometer based on a 0.4 T permanent magnet was characterized. In tandem mass spectrometers, particularly in quadrupole ion traps and FT/ICR instruments, ions have time to isomerize after ionization. The most stable structure of an ion may or may not have the same connectivity as the parent molecule. Collision-induced dissociation and ion-molecule reactions were used to study the structures of the ions of interest. The molecular ions of organophosphorus esters were found to spontaneously and irreversibly rearrange to distonic ions (ions in which the charge and odd spin sites are formally separated). Organophosphorus thioesters, however, do not rearrange after ionization. Reference ions for the enol and distonic structures of ethyl acetate were used to show that ion-molecule reactions are useful for the distinction of these two functionalities. FT/ICR mass spectrometers have typically been based on an electromagnet or a superconducting magnet, which constrains them to electromagnet or a superconducting magnet, which constrains them to floorstanding configurations. By miniaturizing the FT/ICR mass spectrometer, the advantages of this technique, which include high mass resolution, good mass accuracy, the ability to trap ions, and the multiplex advantage, will become accessible to more users. The performance of a small FT/ICR mass spectrometer was characterized. This instrument is based on a 0.4 T permanent magnet and could easily be configured into bench-top proportions. Use of a screened cell was shown to significantly enhance the performance of this instrument. The mass range, the mass resolution, the mass accuracy, the lower limit of detection, and the dynamic range of this mass spectrometer, as well as the stability of the instrument over time and temperature, were determined. Multiple-stage mass spectrometry, the ability to study ion-molecule reactions and to measure a reaction rate constant, were demonstrated.

Degree

Ph.D.

Advisors

Kenttamaa, Purdue University.

Subject Area

Analytical chemistry

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