Ion Hydration and Nanodrops in Mass Spectrometry

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor Evan Williams of the University of California, Berkeley, with his group, will investigate the chemistry and physics of charged droplets and the chemistry that occurs within evaporating droplets. Charged water droplets are ubiquitous in the environment, where they are generated by waves, waterfalls, and in thunderclouds, and have significant importance in industrial processes, including protective coatings, microencapsulation to protect pharmaceutical compounds, and generation of nanoparticles. Electrospray ionization produces highly charged droplets that are used in many of these processes, including as thrusters for positioning spacecraft. It is also an essential analytical method that is used in thousands of laboratories worldwide when combined with mass spectrometry for detailed chemical analysis of complex mixtures, including environmental, synthetic, and biological materials. The project goals are to understand processes that occur with highly charged droplets. This includes droplet fission, whereby droplets spontaneously break up into smaller charged droplets. Experiments aimed at understanding how crystallization occurs in evaporating nanodrops will be pursued to better understand factors that affect both the rates and structures of the initially formed aggregates. Electrospray ionization at reduced pressure will be explored to better understand how droplets are initially formed and what factors affect their initial sizes and charges. This research will take advantage of unique charge detection mass spectrometers that have been developed in the laboratory to mass analyze individual nanoparticles and will likely lead to improved analytical methods, a better understanding of aerosol chemistry that affects the environment and human health, as well as the potential to improve the efficiency of spacecraft thrusters. Students involved in this research learn important skills in chemical analysis, solving complex problems and how to communicate results. These skills are important for the biotechnology, pharmaceutical, and chemical industries. The Williams Lab is studying the chemistry and physics of charged nanodrops with diameters between ~10 nanometers and 1 micron formed using a variety of different methods, including electrospray ionization. Analysis is performed using custom-designed and constructed charge detection mass spectrometers capable of measuring analytes and droplets with masses ranging from a few thousand Daltons to GigaDaltons. Investigations will include measuring the fission processes and dynamics of charged droplets using unique analysis methods to track individual droplet mass and charge that will be developed as part of this project. Effects of solvents and constituents inside the droplets will be investigated to learn how gaseous ions are formed. A reduced-pressure electrospray apparatus will be constructed and evaluated for the potential to extend the current mass range of these instruments and to investigate the initial charged droplet formation process to better understand factors that affect ionization efficiency and selectivity in mass spectrometry. This may also lead to more efficient electrospray-based thrusters. The ability to analyze highly heterogeneous mixtures at high molecular mass makes it possible to investigate the early onset of cluster formation in crystallization. A better understanding of equilibria governing solubility and crystallization has important implications for industrial-scale chemical synthesis. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.