Separations coupled to mass spectrometry (MS) are widely used for large-scale protein identification in order to reduce the adverse effects of analyte ion suppression, increase the dynamic range, and as a deconvolution technique for complex datasets typical of cellular protein complements. In this work, matrix assisted laser desorption-ionization is coupled with ion mobility (IM) separation for the analysis of biological molecules. The utility of liquid-phase separations coupled to MS lies in the orthogonality of the two separation dimensions for all analytes. The data presented in this work illustrates that IM-MS relies on the correlation between separation dimensions for different classes (either structural or chemical) of analyte ions to obtain a useful separation. For example, for a series of peptide ions of increasing mass-to-charge (m/z) a plot drift time in the IM drift cell vs. m/z increases in a near-linear fashion, but DNA or lipids having similar m/z values will have very different IM drift time-m/z relationships, thus drift time vs. m/z can be used as a qualitative tool for compound class identification. In addition, IM-MS is applied to the analysis of large peptide datasets in order to determine the peak capacity of the method for bottom-up experiments in proteomics, and it is found that IM separation increases the peak capacity of an MS-only experiment by a factor of 5-10. The population density of the appearance area for peptides is further characterized in terms of the gas-phase structural propensities for tryptic peptide ions. It is found that a small percentage (~3%) of peptide sequences form extended (i.e., helical or β-sheet type) structures in the gas-phase, thus influencing the overall appearance area for peptide ions. Furthermore, the ability of IM-MS to screen for the presence of phosphopeptides is characterized, and it is found that post translationally modified peptides populate the bottom one-half to one-third of the total appearance area for peptide ions. In general, the data presented in this work indicates that IM-MS offers dynamic range and deconvolution capabilities comparable to liquid-phase separation techniques coupled to MS on a time scale (ms) that is fully compatible to current MS, including TOF-MS, technology.

A Matrix-assisted Laser Desorption/Ionization (MALDI) – Ion Mobility (IM) – Surface-induced Dissociation (SID) – Time-of-Flight (TOF) instrument with three different collision source configurations was developed in order to improve the SID performance in high throughput peptide sequencing. The first version of the instrument was equipped with an angle resolved SID source in order to maximize the collection efficiency of the SID scattering ions. An orthogonal TOF was also implemented as the second MS stage in this instrument to increase mass resolution. The second version of the instrument was developed towards simplifying the coupled configuration of the IM, SID and TOF components by using a combined SID/TOF source with a confinement ring electrode as the collision target. The fragmentation efficiency of SID in this configuration was increased up to 50% due to the surface normal impact angle used as compared with the results from a previous experiment using 45 degree impact angle. The third version of the instrument was equipped with a dual-source/dual-detector TOF to facilitate high throughput tandem analysis of peptides through simultaneous separation, fragmentation and mass analysis, while retaining precursor ion identity in the same experimental sequence. A series of small organic molecules, model peptides and tryptic peptides from a protein digest were analyzed to demonstrate the utility of these new designs for enhanced SID performance and peptide sequencing capability. Finally, a new mobility drift cell using a periodic focusing mechanism has been designed and fabricated to replace the previous uniform field drift cell. Improvement in ion transmission has been observed in the periodic focusing drift cell instrument without sacrificing the mobility resolution.

A Matrix-assisted Laser Desorption/Ionization (MALDI) – Ion Mobility (IM) – Surface-induced Dissociation (SID) – Time-of-Flight (TOF) instrument with three different collision source configurations was developed in order to improve the SID performance in high throughput peptide sequencing. The first version of the instrument was equipped with an angle resolved SID source in order to maximize the collection efficiency of the SID scattering ions. An orthogonal TOF was also implemented as the second MS stage in this instrument to increase mass resolution. The second version of the instrument was developed towards simplifying the coupled configuration of the IM, SID and TOF components by using a combined SID/TOF source with a confinement ring electrode as the collision target. The fragmentation efficiency of SID in this configuration was increased up to 50% due to the surface normal impact angle used as compared with the results from a previous experiment using 45 degree impact angle. The third version of the instrument was equipped with a dual-source/dual-detector TOF to facilitate high throughput tandem analysis of peptides through simultaneous separation, fragmentation and mass analysis, while retaining precursor ion identity in the same experimental sequence. A series of small organic molecules, model peptides and tryptic peptides from a protein digest were analyzed to demonstrate the utility of these new designs for enhanced SID performance and peptide sequencing capability. Finally, a new mobility drift cell using a periodic focusing mechanism has been designed and fabricated to replace the previous uniform field drift cell. Improvement in ion transmission has been observed in the periodic focusing drift cell instrument without sacrificing the mobility resolution.

Separations coupled to mass spectrometry (MS) are widely used for large-scale protein identification in order to reduce the adverse effects of analyte ion suppression, increase the dynamic range, and as a deconvolution technique for complex datasets typical of cellular protein complements. In this work, matrix assisted laser desorption-ionization is coupled with ion mobility (IM) separation for the analysis of biological molecules. The utility of liquid-phase separations coupled to MS lies in the orthogonality of the two separation dimensions for all analytes. The data presented in this work illustrates that IM-MS relies on the correlation between separation dimensions for different classes (either structural or chemical) of analyte ions to obtain a useful separation. For example, for a series of peptide ions of increasing mass-to-charge (m/z) a plot drift time in the IM drift cell vs. m/z increases in a near-linear fashion, but DNA or lipids having similar m/z values will have very different IM drift time-m/z relationships, thus drift time vs. m/z can be used as a qualitative tool for compound class identification. In addition, IM-MS is applied to the analysis of large peptide datasets in order to determine the peak capacity of the method for bottom-up experiments in proteomics, and it is found that IM separation increases the peak capacity of an MS-only experiment by a factor of 5-10. The population density of the appearance area for peptides is further characterized in terms of the gas-phase structural propensities for tryptic peptide ions. It is found that a small percentage (~3%) of peptide sequences form extended (i.e., helical or β-sheet type) structures in the gas-phase, thus influencing the overall appearance area for peptide ions. Furthermore, the ability of IM-MS to screen for the presence of phosphopeptides is characterized, and it is found that post translationally modified peptides populate the bottom one-half to one-third of the total appearance area for peptide ions. In general, the data presented in this work indicates that IM-MS offers dynamic range and deconvolution capabilities comparable to liquid-phase separation techniques coupled to MS on a time scale (ms) that is fully compatible to current MS, including TOF-MS, technology.

During the last decade, the Denton Research Group has made significant advancements in the field of real time direct vapor detection of low volatile explosives under ambient conditions. An ion source plays a crucial role in the sensitive detection of traces of compounds in gas phase by ion mobility spectrometry, but, all the current ionization techniques have significant drawbacks and do not fully satisfy all needs. To overcome the limitations associated with either hazards from a radiogenic ion source or poor reliability from the current non-radiogenic ion sources, the author of this dissertation has undertaken the development of an entirely new ion source based on dielectric barrier discharge technologies. This dissertation describes the development, characterization, and applications of novel dielectric barrier discharge (DBD) ion sources for ion mobility spectrometry. The sources under investigation are non-radiogenic, highly reliable, and provide a high yield of ions. The difficulty of extracting ion current from a traditional dielectric barrier discharge was solved by using an array of tiny discharges formed at the crossing points of two crossed sets of glass coated wires. The relationship of the excitation voltage, frequency, and extraction field for AC excitation on the extracted ion current were studied. The dielectric barrier discharge ion source were also excited in pulse mode by fast-rising and fast-falling high voltage pulses. A high voltage switch using serial MOSFETs was specially designed for driving the dielectric barrier discharge ion source in pulse mode. Application of this dielectric barrier discharge ion source to ion mobility spectrometry was demonstrated with the measurement of limit of detection and direct vapor detection of explosives.

The development of new technologies and the advancement of existing technical expertise can allow for dramatic improvements to be realized in analytical instrumentation. The development of an integrating solid-state ion detector, designed to have a high sensitivity as well as maintaining a high-level of stability, is described and evaluated. Several versions of the charge-transimpedance amplifier (CTIA) technology were constructed with different operating features. The CTIA-1 is a 32-pixel array detector designed for mass spectrometry. It has the capability to simultaneously detect multiple ion channels with a detection limit less than 100 ions. The CTIA-2 detector features an independent selectable gain for each detection channel. The CTIA-2 is a 4-channel device designed for ion mobility. Further design features were built into the CTIA-5 such as differential noise reduction capabilities.The CTIA-1 technology was evaluated for use in isotope ratio mass spectrometry on a custom-built Mattauch-Herzog mass spectrometer. An evaluation was conducted in terms of the detector sensitivity, stability, accuracy, precision, resolution, and mass bias. The CTIA-2 was tested on a sector mass spectrometer for its response to low ion currents of both positive and negative ions. The detector stability, its accuracy, and its precision were studied.The technique of ion mobility spectrometry is rapidly growing, as it is the main technology used for the detection of explosives at security checkpoints. The need to improve the sensitivity of existing ion mobility instruments has led to the exploration of using the CTIA detector in ion mobility instruments. Improvements in sensitivity of two to three orders of magnitude have been demonstrated using the described CTIA detectors. Additional applications that use ion mobility instruments for the detection of analytes have been presented, the chemical mapping of a halogen-contaminated sand bed, the detection of pesticides, as well as the detection of TNT in drinking water.Results indicate that the CTIA detector technology is well suited for use in both mass spectrometry and ion mobility. The sensitive and stable multi-array CTIA detectors perform well in isotope ratio mass spectrometry. Ion mobility instruments of all types can benefit from the added sensitivity supplied by this technology.

No description available.

Thesis (Ph. D.)--Virginia Commonwealth University, 2007. / Prepared for: Dept. of Chemistry. Bibliography: leaves 194-206. Also available online via the Internet.

In this thesis, a miniaturised field asymmetric waveform ion mobility spectrometry (FAIMS) device is combined with mass spectrometry (MS), and liquid chromatography, for the development and application of bioanalytical methodologies. FAIMS is a highly orthogonal to MS and LC and has the potential to enhance both targeted and non-targeted bioanalytical applications. Chapter two demonstrates the capability of the FAIMS combined with mass spectrometry to reduce the complexity of the mass spectrum by separating species of different charge states and overlapping mass-to-charge ratios that are challenging to separate by MS. FAIMS selected transmission shows improvement in signal-to-noise ratios for low intensity species and enables visualisation of species undetectable without FAIMS. Chapter three describes the development of an LC-FAIMS-MS method for the rapid analysis of saliva for the identification of potential biomarkers as a result of oxidative stress. The combination of FAIMS showed a reduction in saliva matrix interferences resulting in improved discrimination and peak integration of two salivary oxypurine compounds in a rapid LC-FAIMS-MS method. Chapter four investigates the FAIMS separation of seven steroid metabolites with a range of cationic adducts, in order to develop a rapid screening LC-FAIMS-MS method for the determination of isobaric steroid metabolites in urine. LC-FAIMS-MS analysis of the steroid metabolites shows improved discrimination of co-eluting and isobaric steroid metabolites with improvements in signal-to-noise ratio with reductions in chemical noise, demonstrating the potential of combining FAIMS with LC-MS. Chapter five demonstrates the potential of FAIMS to increase peak capacity in non-targeted omics applications, by combining rapid compensation field scanning of the FAIMS with ultra-high performance LC-MS. The rapid scanning of the FAIMS allows acquisition of full scan FAIMS and MS nested data sets within the timescale of a UHPLC chromatographic peak, and is applied to the non-targeted profiling of human urine. Improvements in the number of features detected using LC-FAIMS-MS were as a result of reductions in chemical noise and separation of co-eluting isobaric species across the whole analytical space, demonstrating the potential of combining FAIMS with LC and MS.

Anionic metal-oxalate complexes have been generated in the gas phase and an attempt at determining plausible structures were made. Two different experimental techniques were coupled to mass spectrometry: Infrared Multiphoton Dissociation (IRMPD) and ion mobility. Both techniques were compared to theoretical structures calculated using various levels of theory. With the use of IRMPD, frequencies were generated for each complex and compared to theoretical frequencies. Plausible structures for all complexes were found using the M-series of density functional levels of the theory when the 6-311+gd basis set was used and Bhandhlyp functional was appropriate for the lanl2dz basis set. Using ion mobility allowed for collision cross-sections to be calculated and compared to theoretical collision cross-sections of the various structures. Unfortunately no plausible structures were determined using this technique due to a lack of calibrants for the negative mode of ion mobility.