Source: Dissertation Abstracts International, Volume: 55-08, Section: B, page: 3274.

Adviser: Alessandro Gomez.

This thesis presents the primary findings of a series of exploratory efforts to apply the powerful and established technique of Electrospray Ionization Mass Spectrometry (ESMS) to new areas of chemical analysis. All of the studies involved either novel methods of sample preparation and introduction, or the exploitation of operating characteristics inherent to the electrospray ion source design. The results presented not only open up new opportunities for ESMS applications in areas such as trace analysis of air and water, but also add to the growing, but still far from complete, understanding of the fundamental mechanisms involved in electrospray ionization.

Chapter one introduces the basic physical processes of electrospray ionization as well as the basic features of the ESMS system employed in most of these studies. Chapter two details the use of the ESMS in the detection of airborne species, for example chemical warfare agents, which may be present at sub part per billion concentrations. Real time monitoring of trace vapors from explosives or narcotics in the 10 parts per trillion (ppt) level in air appear feasible. The electrospray may also be used for charging and capturing aerosol particles.

Chapter three investigates the application of ESMS to the analysis of metal ions in water. When small amounts of metal bearing water are added to electrosprays of pure organic solvents such as acetonitrile or methanol, solvated metal ions yield intense signals. Sensitivities to metal present at only 50 nanomolar concentrations are inferred. The efficiency with which a gas phase metal ion may be produced in ESMS is demonstrated to be related to its affinity with the solvent. The formation in electrosprays of cluster ions of organic solutes, both large and small, is explored in chapter four. The appearance of the non-covalently bonded 'molecular aggregates' is, as in the case of clustering amino acids, not a simple matter of solubility. The ability of this very soft ionization technique to generate gas phase ions of molecular complexes of biological significance is discussed. Evidence for the formation of a guanosine-actinomycin complex and a gramicidin-cyclosporin complex is shown.

Chapter five details an innovative method for measuring the energy of ion dissociation using the existing electrospray source technology. In the presence of a strong electric field, the normally cold free jet environment is converted into a collision driven furnace capable of decomposing the ions which travel through it. The extent of ion fragmentation, after proper normalization of the data, is interpreted with a unimolecular kinetics argument. Simulation and measurement both indicate that ion excitation in the jet is both extensive and uniform. An unconventional derivation of the high field ion mobility equations lends some physical insight into the phenomenon. This quantitative method can be employed in any high pressure ion source in which free jets are used.