Development of Vibrating Sharp-edge Spray Ionization (VSSI) methods for Mass Spectrometry Analysis and Imaging

Mass Spectrometry (MS) is one of the widely used tools for chemical detection down to attomole concentrations for certain proteins. Ionization sources are a critical component for MS analysis. One of the major ionization methods is electrospray ionization (ESI), which remains a gold standard for proteins and peptides. ESI uses voltages up to ~4 kV to produce ions from solubilized molecules. Recently, a novel ionization method termed vibrating sharp-edge spray ionization (VSSI) that nebulizes liquids efficiently at the edge of a vibrating glass slide has been reported. The work in this thesis leverages the capabilities of VSSI for continuous flow-based analysis, surface chemical analysis, and imaging. Continuous flow is a popular sample introduction format for mass spectrometry (MS) analysis because of its compatibility with liquid chromatography (LC) separations. The first part of the thesis focuses on the development of continuous flow capillary Vibrating Sharp-edge Spray Ionization (cVSSI), which nebulizes liquid samples directly at the outlet of a capillary without using high-speed nebulization gas or an electrical field. We demonstrated two liquid chromatography-mass spectrometry (LC-MS) applications using cVSSI: 1) separation and detection of a mixture of small molecule metabolites; and 2) bottom-up proteomics using a protein digest of cytochrome-C as an example. The limits of detection were 5 nM for acetaminophen and cVSSI did not contribute at all to post-column broadening of the analytes. The second part of the thesis explores direct analysis of chemicals on a surface using a simple and standalone ionization system for the solvent extraction-based surface analysis without the need of high voltage. We modified the original VSSI device and developed a standalone, integrated surface sampling and ionization system for direct MS analysis. We further characterized the performance of this method with a series of compounds and demonstrated a comparable LOD to literature values obtained by desorption electrospray ionization (DESI). For example, the limits of detection were 9 pg/mm2 for the pesticide Ametryn on the surface of spinach leaves. The final part of the thesis focuses on the proof-of-concept of VSSI for mass spectrometry imaging (MSI). We demonstrated that a 100 mM solution of rhodamine B dye that was contact printed as square could be imaged at a resolution of 250 mm. VSSI is presented as an ambient method of extraction of analyte molecules from the surface using an internal standard. Analyte is desorbed from the surface via liquid bridge and the development of instrumentation for imaging application is discussed. Analytical capabilities of the method for imaging applications is presented