Continuous time-of-flight mass spectrometric imaging of fragmented ions

This thesis describes the implementation, characterization, and theoretical analyses of imaging Hadamard transform time-of-flight mass spectrometry (Im-HT-TOFMS). This new technique is based on pseudorandom ion beam modulation and three-dimensional ion imaging, and it provides mass spectra at every "pixel" of a two-dimensional image with 100% duty cycle. This thesis is organized according to three development stages of Im-HT-TOFMS.;The first stage is the two-channel Hadamard transform (HT) time-of-flight mass spectrometry (TOFMS). Although TOFMS offers high sensitivity and mass resolution with pulsed ion sources, it is inherently a pulsed technique and efficient coupling to a continuous ion source presents a technical challenge. Two-channel HT-TOFMS is a multiplexing strategy to achieve very high efficiency through ion beam modulation according a pseudorandom binary sequence. Efficiency close to 100% is achieved using a two-channel detector by simultaneously detecting both states of the binary modulation. The implementation of the technique and theoretical analysis of various figures of merit are presented and discussed. Also, Bradbury-Nielsen gate and a double-stage reflectron, which are two important components of the technique, are described. Although 100% efficiency was possible using the two-channel HT-TOFMS, this was often challenging in practice due to the difficulty of matching the ion beam size and deflection angles to the detector dimensions.;The next stage of development is to employ a three-dimensional imaging detector that can record the positions x, y and flight time t of every ion arrival event. The implementation and characterization of the new Im-HT-TOFMS are described. The technique always has a duty cycle of 100%, and its enhanced peak height precision compared to conventional linear TOFMS is demonstrated. It also has the capability of producing a mass spectrum for every "pixel" of a two-dimensional image of the ion beam. By spatially dispersing different chemical or physical processes, additional information can be obtained. This is demonstrated by imaging the fragmented ions that underwent surface-induced dissociation and post-source decay.;The final development stage is to modulate the fragmentation process using a laser or an electron gun and to measure both the flight time and kinetic energy of the ions. This new technique termed Hadamard transform ion kinetic energy spectrometry (HT-IKES) can be used to provide tandem mass spectra of a mixture of analytes simultaneously. The design principles of HT-IKES are presented.;I expect Im-HT-TOFMS and HT-IKES to be powerful tools for identifying and probing time-dependent chemical processes of analyte mixtures with applications in stopped-flow solution kinetics and fast chromatography.