The computer controlling of the time delay of the extraction of ions from the ion source of the TOF mass spectrometer

Computer control of time delay of the extraction of ions from the ion source of the TOF mass spectrometer is presented. Owing to the computer, the user has the full control of power parameters and ion current delay, which is about microseconds

Multi-photon ionisation spectroscopy for rotational state preparation of N+2

In this paper we investigate the 2 + 1′ resonance enhanced multi-photon ionisation (REMPI) of molecular nitrogen via the a1Πg(v = 6) intermediate state and analyse its feasibility to generate molecular nitrogen ions in a well defined ro-vibrational state. This is an important tool for high precision experiments based on trapped molecular ions, and is crucial for studying the time variation of the fundamental constant mp/me using N+2. The transition is not reported in the literature and detailed spectral analysis has been conducted to extract the molecular constants of the intermediate state. By carefully choosing the intermediate ro-vibrational state, the ionisation laser wavelength and controlling the excitation laser pulse energy, unwanted formation of rotationally excited molecular ions can be suppressed and ro-vibrational ground state ions can be generated with high purity

Off-line MALDI mass spectrometry of bioaerosols

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used for off-line analysis of bioaerosols. The overall goal of the work is to develop methods and instrumentation to minimize sample treatment and maximize sensitivity and selectivity for bioaerosol analysis. This work is divided into three parts: sample preparation, test bioaerosol analysis, and instrument development. Untreated silicon wafer substrates were used as an alternate to conventional stainless steel targets and proved to be excellent substrates for large molecule analyses as well as small molecule analyses with excellent spot-to-spot and shot-to-shot reproducibility, which is useful for high-throughput and automated sample analysis. MALDI sample preparation was optimized by the L9 (33) orthogonal array of Taguchi’s systematic approach using the effects of various parameters such as matrices, solvents, and deposition methods. Test bioaerosol particles were generated from a nebulized bacterial suspension and were collected onto bare or matrix pre-coated MALDI targets placed in an impactor for off-line analysis. The MALDI matrices or solvents were added on the target afterward by pipette or spraying to obtain signals similar to the dried droplet method. Finally, two novel MALDI mass spectrometers were constructed to test new bioaerosol ionization approaches. A transmission geometry MALDI-MS, in which the laser irradiates samples from back side of the target, enabled a tight laser focusing by coupling a microscope objective lens outside of the vacuum. The instrument is applicable to the analysis of single deposited bioaerosol particles. A UV and IR MALDI ion mobility mass spectrometer was used for the analysis of complex bioaerosol mixtures by two-dimensional separation of ions according to their shapes and masses. The instrument separates the complex bioaerosol mixtures into different classes on trend lines that simplify the analysis. These trend lines include lipids, peptides/proteins, and oligonucleotides

Development of an Apparatus for the Study of Electron Impact Fragmentation of Molecular Clusters

The aim of the experiment described in this thesis was to generate a beam of molecular clusters and to look at fragmentation processes induced by low-energy electron impact. These processes are studies by time-of-flight detection of ionised and neutral metastable fragments. A beam of molecular clusters is generated using a pulsed supersonic expansion, and this beam is crossed with a pulsed beam of electrons. The electron pulse is 1 μs to provide the necessary time-of-flight resolution. Ionised fragments are detected using a reflectron time-of-flight mass spectrometer with a microchannel plate detector. Neutral metastable fragments are detected using a channeltron with appropriately biased meshes in front to avoid the detection of charged particles. For both types of fragment data acquisition takes place using a multichannel scaler. Detection of the ions is mass resolved, whereas the flight time of the neutral metastable fragments provides information about the kinetic energy these fragments have acquired in the fragmentation process. The ultimate goal of this experiment is to study lowenergy electron impact on biomolecules solvated in water clusters. This is relevant in the context of radiation damage studies. Recent research on radiation damage in biological organisms has demonstrated the relevance of low-energy secondary electrons produced by the radiation. The work described in this thesis involved the development of a working cluster source, which produces excellent methanol and argon mass spectra, via supersonic expansion from a nozzle. A neutral metastable detector has been designed, constructed, and implemented; time-of-flight spectra have been gathered for electron impact on argon clusters, and are in agreement with previous work, indicating the detector is operating well. The electron gun has been adapted to incorporate a deflection system for steering of the electron beam, and now operates well with stability down to 20 eV. Programs have been written using LabVIEW for control of the electron impact energy, and for the acquisition of data and excitation functions, as well as providing quick analysis of mass spectra. Further minor modifications and implementations have been conducted to optimise the overall operation of the system. This developmental work has moved the apparatus at Maynooth closer to its ultimate goal, the study of electron impact fragmentation of molecular clusters

Development of methods for the detection of chemical and biological warfare agents

This dissertation sought to find conditions that enabled the characterization of weapons of mass destruction, be that chemical, explosives, or biological, and find unique ion signals for those materials. Chapter 2 examines how to improve the analytical capability of the pulsed glow discharge through an increased understanding of the ionization processes inherent to the technique. Results of a parametric evaluation of ionization processes in the plasma demonstrated that within the glow discharge ion source there are conditions that can be determined which will enhance the signal of the analytical ion. A key innovation was the determination, that in constant power operations, optimal analyte signals could be found 6-8 mm in distance from the cathode and at shorter pulse widths and duty cycles. For the first time, the behavior of argon doubly charged species was characterized in these pulsed plasmas. Whereas the goal of Chapter 2 was to understand the fundamental characteristics of the pulsed glow discharge, Chapters 3 and 4 strive to expand its future possibilities through the coupling of gas chromatography and the pulsed glow discharge ion source to achieve chemical speciation. Chemical speciation can be achieved through structural information from the plateau region and molecular ion information from the afterpeak region and both can be acquired simultaneously. The ability of the pulsed glow discharge to acquire both pieces of information gives the analyst a greater degree of confidence in the identification of the compound; no other technique is capable of providing both pieces of information simultaneously. The purpose of these studies was to determine if the time-gated pulsed glow discharge coupled with gas chromatography mass spectrometry could provide adequate information to detect a chemical warfare agent metabolite or an explosive related compound. We were able to demonstrate that the pulsed glow discharge provides structural information during the plateau for the analytes and we learned that it was important to control the analyte concentration introduced to the plasma so that it does not quench the afterpeak signal. Future directions would focus on lowering the analyte concentration sufficiently. In Chapter 5, we hypothesized that the separation of particles by size would enhance the ability to discriminate between different sources of a Bacillus anthracis surrogate. Size selection was combined with analytical techniques to enhance the capability of identifying biological signatures of bacterial spores. It was found that size separation permitted a more rapid determination by SEM to confirm the presence of spores, but did not enhance the ability of Raman to identify the spores. Ultimately, results from these analyses can be used to build a library to determine an organism\u27s unique biological signature that can be correlated with known growth and processing methods to identify how, when, and where the sample was produced

Characterisation of Cold and Isolated Biomolecules

Gas phase infrared (IR) spectroscopy has emerged as a powerful method to study (bio)molecules in the absence of influences from external factors in the liquid or solid phase. However, the low number density of analytes in the gas phase requires a change in measurement principle. Instead of monitoring the attenuation of IR radiation upon interaction with the analyte, the effect of the irradiation on the analyte has to be monitored. Different concepts to realise this so called action spectroscopy have been realised to date. In this thesis, a novel instrument to perform gas phase IR spectroscopy is introduced. Based on an ion mobility mass spectrometer conceived earlier, the instrument aims to combine the complementary techniques of ion mobility spectrometry and mass spectrometry for a sophisticated selection of ions for IR spectroscopy. After ion mobility and mass selections, ions are rapidly cooled to the temperature of a cryogenic ion trap by collisions with a buffer gas. The loss of energy upon colliding with the buffer gas does not only enable trapping of ions in the cryogenic ion trap, the low temperatures in the cryogenic ion trap also allows for the attachment of molecular tags. These molecular tags serve as messengers for the subsequent messenger tagging IR spectroscopy. A pulsed beam of cooled and tagged ions will be created upon ejection from the cryogenic ion trap and is subsequently overlaid with the IR radiation provided by the Fritz Haber Institute Free Electron Laser (FHI FEL). By scanning the wavelength of the FEL, the different vibrational modes of the ions can be probed. Excitation of vibrational bands in the analyte can be detected as the depletion of a messenger tag: absorption of a resonant photon is dissipated throughout the molecule by intramolecular vibrational energy redistribution and subsequently to the surrounding by the loss of an attached messenger. The ratio of messenger tagged and messenger tag depleted ions can be determined from using time-of-flight mass spectrometry. In this work, individual parts of iMob 2.0 are explained in detail. The systematic characterisation of the cryogenic ion trap as a central part of the machines initial commissioning will be highlighted. Furthermore, the performance and potential of messenger tagging IR spectroscopy will be evaluated using the pentapeptide leucine-enkephalin (LEK). In comparison to IR spectra obtained by two different types of action spectroscopy, namely IR multiphoton dissociation (IRMPD) spectroscopy and infrared (IR) spectroscopy using helium nanodroplets, the IR spectrum obtained from the messenger tagging approach can be benchmarked. In addition to LEK, two isomeric trisaccharides of the Lewis antigen class will be subject to IR spectroscopic experiments. The migration of inherent fucose moieties in these biologically relevant molecules remains puzzling and the ability to distinguish ions of the same mass by ion mobility spectrometry holds the promise to selectively shed light onto the observed rearrangement.Infrarot (IR) Spektroskopie in der Gasphase etabliert sich zunehmend auch in der Analyse von großen (Bio)Molekülen. Dabei liegt der Vorteil gegenüber IR Spektroskopie in Lösung oder am Feststoff darin, dass externe Störeinflüsse besser vermieden werden können. Ein inhärentes Problem von Gasphasen IR Spektroskopie ist jedoch die geringe Teilchendichte. Zur Überwindung dieser Problematik hat sich das Prinzip der Wirkungsspektroskopie durchgesetzt. Dabei wird nicht der Einfluss der Probe auf das eingestrahlte Licht verfolgt, sondern es wird beobachtet welchen Einfluss das Licht auf die Strahlung hat. Im Rahmen dieser Arbeit wird ein Gerät beschrieben, das eine Umsetzungsmöglichkeit zur Wirkungsspektroskopie realisiert. Dabei wurde ein schon bestehendes Messgerät für Ionenmobilitäts- und Massenspektrometrie dahingehend erweitertet, dass es für Reporter Spektroskopie geeignet ist. Die Selektion von Ionen mittels Ionenmobilitäts- und Massenspektrometrie ist dabei komplementär und erlaubt Spektroskopie an sehr selektierten Ionen. Dafür werden diese in einer kalten Ionenfalle durch die Kollision mit einem Puffergas abgebremst und auf die Temperatur der Falle gekühlt. Dabei ermöglichen die niedrigen Temperaturen in der Ionenfalle das nichtkovalente Anlagern von inerten Reportermolekülen, welche für das Messprinzip essentiell sind. Durch gepulste Ejektion aus der Ionenfalle entsteht ein Ionenstrahl, welcher mit der IR Strahlung des Freien Elektronen Lasers (FEL) des Fritz Haber Instituts (FHI) überlagert werden kann. Dabei führt das resonante Anregen von Schwingungsbanden in den Molekülionen dazu, dass, durch Umverteilung der Schwingungsenergie, das Reportermolekül abgelöst wird. Dieser Verlust des Reportermoleküls lasst sich in einem Flugzeitmassenspektrometer detektieren und erlaubt aus dem Verhältnis zwischen Ionen mit und ohne Reportermolekül bei einer definierten Wellenzahl ein IR Spektrum zu ermitteln. In dieser Arbeit werden die einzelnen Bauteile des iMob 2.0 beschrieben und in das Experiment eingeordnet. Es folgt eine systematische Evaluation einiger Parameter der kalten Ionenfalle, die sozusagen das Herzstück der Apparatur darstellt. Um das Potential der IR Spektroskopie am iMob 2.0 abschätzen zu können, wird das Pentapeptide Leucin-Enkephalin benutzt, welches bereits mit zwei anderen Varianten der Wirkungsspektroskopie, IR Vielphotonen-Dissoziation Spektroskopie und IR Spektroskopie in Helium Nanotröpfchen, untersucht wurde. Außerdem werden Trisaccharide aus der Gruppe der Lewis Antigen hinsichtlich der beobachteten Umlagerung von Fucose-Einheiten untersucht. Da noch nicht verstanden ist, wie diese Migration im Detail funktioniert, ist das iMob 2.0 durch IR Spektroskopie nach Selektion isomerer Verbindungen aufgrund unterschiedlicher Ionenmobilitäten dazu prädestiniert das Verständnis dieses Phänomens zu erweitern

Field emission of ZnO nano-structures produced by laser ablation

The thesis describes the development of, and results from, two new laboratory facilities designed to investigate the properties of laser produced plasmas, with in-situ time of flight mass spectrometry, for deposition of ZnO materials for applications as field electron emission sources. The results from the work are concerned with the study of the important physical processes present in a laser ablation zinc oxide plasma plume expanding into vacuum and various ambient gas pressures. The thesis also demonstrated the advantages of combining a linear ToF detector and a mass resolved ReToF spectrometer for clarification of ionisation processes in the pulsed laser ablation regime of solid targets. The outstanding results show that during the ablation process, ZnO atomises into Zn and O. In the vacuum regime we have shown that at long distances from the target multiple charged states of Zn and O are present. While under the same conditions in an ambient gas the multiple charged states are not present, however the ambient gas undergoes an ionisation process. Deposited materials are tested for applications as field electron emission sources, for analysis of field enhancement factors from nano-material ZnO