Graduation Year

2020

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Chemistry

Major Professor

Theresa Evans-Nguyen, Ph.D.

Committee Member

Andreas Muller, Ph.D.

Committee Member

Abdul Malik, Ph.D.

Committee Member

John Koomen, Ph.D.

Keywords

Surface Acoustic Wave Nebulization, Atmospheric Pressure Chemical Ionization, Bulk Acoustic Wave Nebulization, Rapid Analysis, Ion-trap Analyzer, Orbitrap Analyzer

Abstract

Ambient desorption/ionization techniques (ADI) have drawn significant attention in mass spectrometric instrumentation development. The analyte classes that are successfully studied by any ADI mass spectrometry (MS) method strongly depends on how gas-phase ions are generated. Spray-based techniques may ionize molecules across a wide range of mass-to-charge ratios, but are commonly used for polar analyte, however, suffers from severe matrix effect. Contrastingly, methods employing electric (or laser) plasmas are capable of ionization of polar and nonpolar analytes suffering from less matrix effect, but primarily targeting those with low molecular masses. Thus far, developments of universal ionization methods, which do not depend on the polarity or the molecular weight of the analyte, are still of high demand.

A novel technology termed surface acoustic wave nebulization (SAWN) has been demonstrated as a self-contained ionization source for MS. The coupling of SAWN with corona discharge (CD) as a novel direct mass-spectrometric method significantly improved ion signals by up to 4-orders of magnitude obviating the need for modifications of mass spectrometers (e.g., adding an ion funnel). Importantly, CD was found to be capable of interacting with the fine droplets produced by a SAWN device. This combination produces intact molecular ions, and even doubly charged peptides, demonstrating the potential applicability of SAWN-CD towards real-life applications involving complex samples. Unfortunately, the complexity of SAWN and its high cost limited its potential users from accessing such devices. Herein, we reported on an analogous implementation of CD with an inexpensive ultrasonic nebulizer (USN) based on a commercial room humidifier demonstrating equivalent performance. We subsequently compared the two methods of SAWN-CD and USN-CD in a screening application of milk for the detection of two antibiotic drugs, ciprofloxacin and ampicillin. In addition to the chemical information reflected in the m/z domain, an automated workflow based on a modified cross-correlation algorithm was adapted to ideally form extracted categories of ions that are associate with the same chemical origins.

Download

Share

COinS