Author ORCID Identifier

https://orcid.org/0000-0002-2076-197X

Semester

Fall

Date of Graduation

2022

Document Type

Thesis

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Chemistry

Committee Chair

Stephen J. Valentine

Committee Co-Chair

Peng Li

Committee Member

Harry Finklea

Committee Member

Carsten Milsmann

Committee Member

Tatiana Trejos

Abstract

In recent years the mass spectrometry (MS) area of field and/or direct analysis has grown dramatically. As a result, field-portable and miniaturized mass spectrometers, introduced only a few years ago, are proliferating. A highly desired feature for field-portable MS, or in-field analysis, is the ability to use ionization techniques requiring very little sample preparation as well as an ability to generate the ions under ambient conditions. Recently, a new ambient ionization technique termed vibrating sharp-edge spray ionization (VSSI) has been introduced which overcomes the field-portable limitations of other spray-based methods including the requirements for auxiliary components (e.g., nebulizing gas and high voltage). As a new ambient ionization technique with significant potential for field-portable and direct analyses, it is important that the chemical and physical properties of the VSSI technique be elucidated to optimize ion production performance. Here, experimental and theoretical studies provide insight into the influence of analyte and solvent molecule properties on the production of ions. In Chapter 2, experiments employing protic solvents demonstrate that different analyte molecular properties are associated with increased ionization for VSSI methods compared with gold standard electrospray ionization (ESI) techniques; for VSSI methods correlations are observed for ion intensity and molecule proton affinity and polarity are observed which are absent for ESI. In Chapter 3, experiments employing acetonitrile as the solvent also reveal difference between VSSI and ESI techniques. For example, remarkably in positive ion mode, greater ion signals are observed for voltage-free VSSI compared with ESI. Additionally, analyte proton affinity exhibits an outsized relationship with ionization compared with protic solvents. In Chapter 4, molecular dynamics (MD) simulations of water droplets suggest that the energy of desorption of the ions can account for differences in voltage-free and field-enabled VSSI. Further MD studies provide some support of analyte polarity influencing ionization efficiency. Finally, Chapter 5 provides some direction for improving VSSI experiments and hardware to allow the clear elucidation of primary factors driving compound ionization.

Embargo Reason

Publication Pending

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