Giessen, Universiẗat, Diss., 2004.

Frankfurt (Main), Universiẗat, Diss., 2003.

A novel laser desorption system, with improved signal stability and extraordinary long lifetime, is presented for the study of jet cooled biomolecules in the gas phase using vibrationally resolved photoionisation spectroscopy. Tryptophan (Trp) is used as the test substance to characterize this desorption source. Here, the surface of a moving and rotating rod (graphite/Trp, 3mm diameter and 6 mm length) is exposed to a pulsed desorption beam from a Nd:YAG (1064 nm) laser running at 20Hz (Continuum Minilite).The characteristics of the source developed here and its properties with respect to cooling and stability have been investigated. Good control over the rod movement and the delivery of the IR beam result in a highly stabilized source with no noticeable fragmentation products.The combination of premixing within the source and using a pellet has made it possible to produce a stable jet-cooled beam of Trp, which lasts for several weeks without changing the sample. Additionally, the stability and signal to noise ratio has been improved by averaging the signal over the entire sample pellet by synchronizing the data acquisition with the rotation of the sample rod. The results demonstrate how a combination of the above helps to produce stable time of flight (TOF) signal and good quality one- and two-colour resonant two-photon ionisation (R2PI), photoionisation efficiency (PIE) and mass analyzed threshold ionization (MATI) spectra of Trp. The existence of six low-lying conformers of Trp in the gas phase has been confirmed. The first MATI spectrum of an isolated biomolecule (Trp) via R2PI for the determination of IE with high accuracy as ± 3 cm-1 has been recorded.

No description available.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 5 uppsatser.

Ko Ka Lung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Abstracts in English and Chinese. / Title page --- p.i / Abstract (English) --- p.ii / Abstract (Chinese) --- p.iii / Acknowledgement --- p.iv / Declaration --- p.v / Table of Content --- p.vi / List of Figure --- p.viii / Chapter 1. --- INTRODUCTION --- p.1 / Chapter 1.1 --- Matrix-assisted Laser Desorption / Ionization (MALDI) --- p.2 / Chapter 1.1.1 --- Evolution of Matrix-assisted laser desorption / ionization (MALDI) --- p.2 / Chapter 1.1.1.1 --- Lasers --- p.3 / Chapter 1.1.1.2 --- Matrices --- p.3 / Chapter 1.1.1.3 --- Sample preparation --- p.4 / Chapter 1.1.1.4 --- Desorption --- p.6 / Chapter 1.1.1.5 --- Ionization --- p.7 / Chapter 1.2 --- Fourier Transform Ion Cyclotron Resonance Mass Spectrometry with MALDI (FTICR-MS) --- p.9 / Chapter 1.2.1 --- History of Fourier Transform Ion Cyclotron Resonance Mass Spectrometry --- p.9 / Chapter 1.2.2 --- Basics of FTICR-MS --- p.11 / Chapter 1.2.3 --- FTICR couple with external ionization source --- p.15 / Chapter 1.2.4 --- Coupling of MALDI to FTICR --- p.16 / Chapter 1.3 --- Problems encountered on the coupling of MALDI to FTICR-MS --- p.17 / Chapter 1.4 --- Outline of present work --- p.19 / Chapter 2 --- SIMULATION METHOD --- p.20 / Chapter 2.1 --- Overview of the ion optics simulation --- p.21 / Chapter 2.2 --- History of SIMION Program --- p.22 / Chapter 2.3 --- Basics and theory of SIMION version 6.0 --- p.24 / Chapter 2.4 --- Simulation method --- p.26 / Chapter 2.4.1 --- Creating potential array --- p.27 / Chapter 2.4.2 --- User program --- p.29 / Chapter 2.4.3 --- Ion definition parameter --- p.31 / Chapter 2.4.4 --- Trajectories quality panel --- p.33 / Chapter 2.4.5 --- Data recording --- p.36 / Chapter 3 --- OPTIMIZATION OF RF-ONLY HEXAPOLE UNDER PULSE GAS CONDITION --- p.37 / Chapter 3.1 --- Introduction --- p.38 / Chapter 3.2 --- Simulation conditions --- p.39 / Chapter 3.3 --- Results and discussion --- p.40 / Chapter 3.3.1 --- rf-frequency (w) --- p.41 / Chapter 3.3.2 --- rf voltage (Vo-p) --- p.44 / Chapter 3.3.3 --- Pulse gas pressure(po) --- p.47 / Chapter 3.3.4 --- Trapping potential (VT) --- p.49 / Chapter 3.3.5 --- Effect of space charge --- p.53 / Chapter 3.4 --- Conclusions --- p.60 / Chapter 4 --- OPTIMIZATION OF DIFFERENT HEXAPOLE-BASED INTERFACES FOR PRE-TRAPPING COOLING --- p.61 / Chapter 4.1 --- Introduction --- p.62 / Chapter 4.2 --- Simulation conditions --- p.63 / Chapter 4.3 --- Results and discussion --- p.66 / Chapter 4.3.1 --- Static medium pressure interface --- p.66 / Chapter 4.3.1.1 --- Effect of pressure --- p.66 / Chapter 4.3.1.2 --- Effect of space charge --- p.70 / Chapter 4.3.2 --- Differential pressure model (Skimmer-based) --- p.73 / Chapter 4.3.2.1 --- Effect of pressure --- p.73 / Chapter 4.3.2.2 --- Effect of space charge --- p.76 / Chapter 4.3.3 --- A comparison of the optimal operating conditions for the three proposed interfaces --- p.81 / Chapter 4.3.4 --- Comparison of the theoretical results amd the experimental results --- p.83 / Chapter 4.4 --- Conclusion --- p.84 / Chapter 5 --- CONCLUSIONS --- p.85 / Chapter 5.1 --- Conclusions --- p.86 / REFERENCES --- p.R1 / APPENDIX --- p.A1

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The thesis is divided into four sections. 1. Sample-first preparation: A method for surface-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of cyclic oligosaccharides¡GIn this work, we report the application of a sample first preparation method for the analysis of cyclic oligosaccharides when using bare AuNPs as the assisted matrix. In the sample first method, the analyte is deposited first and then followed by the bare AuNPs. The cyclic oligosaccharides, including £\-, £]-, and£^-cycodextrin (CD), are difficult to ionize by MALDI-MS, but they could be cationized very efficiently using bare AuNPs as matrixes in combination with a sample first preparation method. The sample first method not only provides high sensitivity for the measurement of neutral carbohydrate but also improves the spot homogeneity. This practical method was further validated by the analyses of biological samples, including neutral carbohydrate, neutral steroid, aminothiols, and peptides. 2. Gold nanoparticles as assisted matrix for detecting small biomolecules from high salt solutions through laser desorption/ionization mass spectrometry¡GThe neutral steroid and carbohydrates, which are difficult to be ionized by using MALDI, but cationized very efficiently by SALDI coupled with the sample first preparation method even if they are dissolved in a high-concentration NaCl solution. Under identical conditions, this practical method was further validated by the analysis of indolamines and peptides. It has also been utilized to analyze the small biomolecules in urine samples. 3. Phosphate-modified TiO2 nanoparticles for selective detection of dopamine, levodopa, adrenaline, and catechol based on fluorescence quenching¡GIn contrast to these studies, we report a simple approach for the selective detection of DA, L-DOPA, and adrenaline by phosphate-modified TiO2 (P-TiO2) NPs in the presence of fluorescein. After the binding of DA, the P-TiO2 NPs become neutral and even positively charged. The adsorption of fluorescein on the particles results in the quenching of fluorescein by TiO2-DA complexes, which have strong absorption at 428 nm. By monitoring the decreases in fluorescence at 520 nm for fluorescein, we calculated the limits of detection (LODs) for DA, L-DOPA, and adrenaline at a signal-to-noise (S/N) ratio of 3, which were 33.5, 81.8, and 20.3 nM, respectively. The results imply that the proposed methods have great potential for use in the selective analysis of catecholamines in biological samples and clinical applications. 4. Sodium hydroxide as pretreatment and fluorosurfactant-capped gold nanoparticles as sensor for the highly selective detection of cysteine¡G Under acidic conditions, fluorosurfactant (FSN)-capped AuNPs are aggregated in the presence of homocysteine (HCys) and cysteine (Cys) but not in the presence of cysteinylglycine, glutathione, and £^-glutamycysteine. When adding NaOH to a solution of HCys, the five-membered ring transition state is formed through intramolecular hydrogen abstraction. By contrast, it is difficult for Cys to form a fourmembered ring transition state after Cys has been pretreated with NaOH. As a result, the HCys-induced aggregation of the FSN-capped AuNPs is suppressed because the five-membered ring transition state exhibits relatively larger steric hindrance and has stronger interaction with the FSN molecules. Thus, we can discriminate between Cys and HCys on the basis of different aggregation kinetics. Under the optimum condition, we have validated the applicability of our method through the analyses of Cys in urine samples. It is believed that this approach has great potential for the detection of Cys in biological samples.

Thesis (Ph. D.)--Drexel University, 2004. / Includes abstract and vita. Includes bibliographical references.

In clinical diagnosis and fermentation industries there is a need for a method that allows for the differentiation of yeast to the strain level (biotyping). The ideal biotyping method should be accurate, simple, rapid and cost-effective, and capable of testing a large number of yeast isolates. Matrix assisted laser desorption/ionization time of flight mass spectrometry has emerged as a powerful biotyping tool for the identification of bacteria and clinical yeast isolates, mainly Candida. It has been found that the MALDI-TOF MS signals from yeast are harder to obtain than from bacteria. It has been reported by several research studies that a cell lysis step is required to obtain a mass spectral signal for clinical Candida strains. To date an optimized sample preparation protocol has not been devised for the biotyping of S. cerevisiae strains. Studies on the identification of yeast using MALDI-TOF MS have focused primarily on clinical Candida yeast isolates but have included very few S. cerevisiae strains. Furthermore these yeast identification studies using MALDI-TOF MS have only achieved identification to the species and not strain level. A major limiting attribute of MALDI-TOF MS for the accurate identification of microbes, is its dependency on a comprehensive mass spectral database. Bruker Daltonics is a pioneer and leader in providing innovative life science tools based on mass spectrometry thus the Bruker Daltonics mass spectral database and state-of-the-art instruments and accompanying software were selected for this study. The Bruker Daltonics mass spectral database currently holds three thousand seven hundred and forty microorganisms of which only a mere seven are S. cerevisiae strains. Initially in this study, a number of parameters of a generic ethanol/formic acid protein extraction procedure as originally described by Bruker Daltoincs were considered in the development of a sample preparation protocol that yielded characteristic and highly reproducible MALDI-TOF mass spectra. The parameters considered included cell number, alcohol fixation, matrix solution and media. It was found that using the optimized sample preparation protocol unique and highly reproducible mass spectral profiles were obtained for all three S. cerevisiae strains. Multivariate analysis confirmed that the differences between all three S. cerevisiae strains were statistically significant. For quality assurance, the spectra of the three strains were sent for evaluation by Bruker Daltonics and were deemed suitable for the purpose of biotyping. The newly created ethanol/formic acid extraction procedure was used to generate an S. cerevisiae mass spectral database comprising of forty-five S. cerevisiae strains within a local context but also of global significance. The accuracy of the mass spectral database was assessed using blind coded S. cerevisiae strains obtained from the Agricultural Research Council Infruitec-Nietvoorbij (Institute for Deciduous Fruit, Vines and Wine), Stellenbosch, South Africa. It was found that S. cerevisiae identification to the species and more importantly strain level was achievable with relatively good accuracy. To determine the potential application of MALDI-TOF MS as an accurate method for S. cerevisiae strain identification in industry, blind coded S. cerevisiae strains were obtained from Natal Cane Products and subjected to MALDITOF MS analysis. It was found that four of the pure cultures submitted were correctly identified to the strain level and the three S. cerevisiae strains incorrectly identified may have been contaminants or the result of incorrect optimization conditions for the fermentation. Thus MALDITOF MS was shown to be an accurate identification tool, that may also be used to detect contaminants or incorrect environmental conditions which can result in substantial losses. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2011.