Microdroplets: Chemistry, Applications and Manipulation Using Ionization Sources and Mass Spectrometry

Abstract

There is widespread use of ionization sources (ambient and non-ambient) for a variety of applications. More recently, charged microdroplets generated by electrospray ionization and paper spray have been used to conduct chemistry at faster rates compared to bulk volumes. Uncharged droplets such as those generated by the Leidenfrost technique have also been used to explore chemistry and study the degradation of drugs in an accelerated manner. These microdroplets serve as reaction vessels in which in which some reactions are known to occur at accelerated rates. Such chemistry can be particularly useful in pharmaceutical settings to rapidly synthesize small amounts of materials in relatively short amount of time. Additionally, microdroplets may also be used to perform high throughput screening analysis. While several parameters influencing the rate of reaction in microdroplets have been explored (such as spray distance and reagent concentration), the mechanism of reaction acceleration has not been probed to a significant extent. A major portion of my dissertation describes the use of charged and uncharged microdroplets to perform quick chemistry, guide microfluidic synthesis of drugs such as diazepam, perform scale up of copper catalyzed C-O and C-N coupling reactions and screen reaction conditions for pharmaceutically relevant reactions such as the Suzuki cross-coupling reaction. Additionally, work discussed here also describes development and use of existing techniques such as structured illumination microscopy to measure droplet sizes, explore the role of distances on droplet size, and study the effect of surfactants on the rate of reactions in microdroplets generated by nano-electrospray ionization. A mathematical model to understand the mechanism of increased reaction rates in microdroplets has also been presented. Additionally, this dissertation also describes ways to manipulate ions in air using various designs of 3D-printed electrodes that operate with DC potentials only and which can be easily coupled with nano-electrospray ionization sources to transmit ions over long distances